A series of drained and undrained water-saturated constant mean-stress tests were performed to investigate the strength, elasticity, and poroelastic response of a water-saturated high porosity nonwelded tuff. Drained strengths are found to increase with increasing effective confining pressures. Elastic moduli increase with increasing mean stress. Undrained strengths are small due to development of high pore pressures that generate low effective confining pressures. Skempton’s values are pressure dependent and appear to reflect the onset of inelastic deformation. Permeabilities decrease after deformation from ∼ 10–14 to ∼ 10–16 m2 and are a function of the applied confining pressure. Deformation is dominated by pore collapse, compaction, and intense microfracturing, with the undrained tests favoring microfracture-dominant deformation and the drained tests favoring compaction-dominant deformation. These property determinations and observations are used to develop/parameterize physics-based models for underground explosives testing.
Treatment of lost circulation can represent anywhere from 5 to 25 % of the cost in drilling geothermal wells. The cost of the materials used for lost circulation treatment is less important than their effectiveness at reducing fluid losses. In geothermal systems, the high temperatures (>90 °C) are expected to degrade many commonly used lost circulation materials over time. This degradation could compromise different materials ability to mitigate fluid loss, creating more non-productive time as multiple treatments are needed, but may result in recovering desired permeability zones within the reservoir section over time. This research aimed to study how thermal degradation of eight different lost circulation materials affected their properties relevant to sealing loss zones in geothermal wells. Mass loss experiments were conducted with each material at temperatures of 90–250 °C for 1–42 days to measure the breakdown of the material at geothermal conditions, collecting gases during several experiments to determine the waste produced during degradation. Compaction experiments were conducted with the degraded materials to show how temperatures reduced the rigidity and increased packing of the materials. Viscosity tests were conducted to show the impact of different materials on drilling fluid rheology. Microscope observations were conducted to characterize the alterations to each material due to thermal degradation. Organic materials tend to degrade more than inorganic materials, with organics like microcellulose, cotton seed hulls and sawdust losing 30–50 % of their mass after 1 day of heating at 200 °C, while inorganics like magma fiber only lose ∼5–10 % of its mass after one day of heating at 200 °C. Granular materials are the strongest when compacted despite any mass loss, while fibrous and flaky materials are fairly weak and breakdown easily under stress. The materials do not generally affect fluid rheology unless they have a viscosifying agent as part of the mixture. Microscopic analysis showed that more rigid materials like microcellulose and cedar fiber degrade in brittle manners with splitting and fracturing, while others like cotton seed hulls degrade in more ductile manners forming meshes or clumps of material. The thermal breakdown of lost circulation materials tested suggests that each material should also be classified by its degree of thermal degradability, as at certain temperatures the materials can lose the capability to bridge loss zones around the wellbore.
The Ghareb Formation is a shallowly buried porous chalk in southern Israel that is being considered as a host rock for a geologic nuclear waste repository. Setup and operation of a repository will induce significant mechanical, hydrological and chemical perturbations in the Ghareb. Developing a secure repository requires careful characterization of the rock behavior to different loads. To characterize hydromechanical behavior of the Ghareb, several short- and long-term deformation experiments were conducted. Hydrostatic loading tests were conducted both dry and water-saturated, using different setups to measure elastic properties, time-dependent behavior, and permeability. A set of triaxial tests were conducted to measure the elastic properties and rock strength under differential loading at dry and water-saturated conditions. The hydrostatic tests showed the Ghareb began to deform inelastically around 12–15 MPa, a relatively low effective pressure. Long-term permeability measurements demonstrated that permeability declined with increasing effective pressure and was permanently reduced by ~ 1 order of magnitude after unloading pressure. Triaxial tests showed that water saturation significantly degrades the rock properties of the Ghareb, indicating water-weakening is a significant risk during repository operation. Time-dependent deformation is observed during hold periods of both the hydrostatic and triaxial tests, with deformation being primarily visco-plastic. The rate of deformation and permeability loss is strongly controlled by the effective pressure as well. Additionally, during holds of both hydrostatic and triaxial tests, it is observed that when water-saturated, radial strain surpassed axial strain when above effective pressures of 13–20 MPa. Thus, deformation anisotropy may occur in situ during operations even if the stress conditions are hydrostatic when above this pressure range.
Nakagawa, Seiji; Kibikas, William M.; Chang, Chun; Kneafsey, Timothy; Dobson, Patrick; Samuel, Abraham; Bruce, Stephen; Kaargeson-Loe, Nils; Bauer, Stephen J.
The Ghareb Formation in the Yasmin Plain of Israel is under investigation as a potential disposal rock for nuclear waste disposal. Triaxial deformation tests and hydrostatic water-permeability tests were conducted with samples of the Ghareb to assess relevant thermal, hydrological, and mechanical properties. Axial deformation tests were performed on dry and water-saturated samples at effective pressures ranging from 0.7 to 19.6 MPa and temperatures of 23 ℃ and 100 ℃, while permeability tests were conducted at ambient temperatures and effective pressures ranging from 0.7 to 20 MPa. Strength and elastic moduli increase with increasing effective pressure for the triaxial tests. Dry room temperature tests are generally the strongest, while the samples deformed at 100 ℃ exhibit large permanent compaction even at low effective pressures. Water permeability decreases by 1-2 orders of magnitude under hydrostatic conditions while experiencing permanent volume loss of 4-5%. Permeability loss is retained after unloading, resulting from permanent compaction. A 3-D compaction model was used to demonstrate that compaction in one direction is associated with de-compaction in the orthogonal directions. The model accurately reproduces the measured axial and transverse strain components. The experimentally constrained deformational properties of the Ghareb will be used for 3-D thermal-hydrological-mechanical modelling of borehole stability.
A critical parameter for the well integrity in geothermal storage and production wells subjected to frequent thermal cycling is the interface between the steel and cement. In geothermal energy storage and energy production wells an insulating cement sheath is necessary to minimize heat losses through the heat uptake by cooler rock formations with high thermal conductivity. Also critical parameters for the well integrity in geothermal storage and production wells subjected to frequent thermal cycling is the interface between metal casing and cement composite. A team from Sandia and Brookhaven National Labs is evaluating special cement formulations to facilitate use during severe and repeated thermal cycling in geothermal wells; this paper reports on recent finding using these more recently developed cements. For this portion of the laboratory study we report on preliminary results from subjecting this cement to high temperature (T> 200°C), at a confining pressure of 13.8 MPa, and pore water pressure of 10.4 MPa. Building on previous work, we studied two sample types; solid cement and a steel cylinder sheathed with cement. In the first sample type we measured fluid flow at increasing elevated temperatures and pressure. In the second sample type, we flowed water through the inside of the steel cylinder rapidly to develop an inner to outer thermal gradient using this specialized test geometry. In the paper we report on water permeability estimates at elevated temperatures and the results of rapid thermal cycling of a steel/cement interface. Posttest observations of the steel-cement interface reveal insight into the nature of the steel/cement bond.
The main goal of this project was to create a state-of-the-art predictive capability that screens and identifies wellbores that are at the highest risk of catastrophic failure. This capability is critical to a host of subsurface applications, including gas storage, hydrocarbon extraction and storage, geothermal energy development, and waste disposal, which depend on seal integrity to meet U.S. energy demands in a safe and secure manner. In addition to the screening tool, this project also developed several other supporting capabilities to help understand fundamental processes involved in wellbore failure. This included novel experimental methods to characterize permeability and porosity evolution during compressive failure of cement, as well as methods and capabilities for understanding two-phase flow in damaged wellbore systems, and novel fracture-resistant cements made from recycled fibers.
The Zenifim Formation is being considered as a potential disposal formation for a deep borehole nuclear repository concept in Israel. Site selection and repository construction are intended to ensure that waste is separated from circulating groundwater, but long-term deformation of the wellbore could potentially create fluid flow pathways. To understand how time-dependent rock strength could affect wellbore stability, we conducted creep tests under low to moderate confining pressures on retrieved core from the Zenifim formation. During creep, samples strain slowly as gradual damage accumulation progressively weakens the samples. Failure eventually occurred through the near-instantaneous formation of a shear fracture. Experimental results were used to calibrate a continuum damage poro-elastic model for sandstones. The calibrated damage-poro-elastic model successfully simulates different types of loading experiments including quasi-static and creep. The state of strain in experiments is close to yield during loading as the yield cap continuously evolves with damage accumulation. For creep tests, most damage occurs during triaxial loading. Minor damage accumulation occurs under constant load until the final stage of creep, where damage accelerates and promotes unstable fracturing.
Geomechanics and Geophysics for Geo-Energy and Geo-Resources
Shalev, Eyal; Bauer, Stephen J.; Homel, Michael A.; Antoun, Tarabay H.; Herbold, Eric B.; Levin, Harel; Oren, Gal; Lyakhovsky, Vladimir
The existence of a deep borehole in the Earth’s crust disturbs the local stresses and creates a stress concentration that may result in breakout and damage to the borehole. Maintaining wellbore integrity mitigates environmental impacts such as groundwater contamination, gas leakage to the atmosphere, and fluid spills and seepage at the surface. In this paper, the stability of deep boreholes (5 km) is examined by laboratory experiments and numerical models in the context of nuclear waste disposal in Israel. Two rock types in southern Israel are considered: the crystalline basement (granite) and the Zenifim Formation (arkose). A series of room-temperature triaxial rock deformation experiments were conducted at different confining pressures. This mechanical characterization was then used to parameterize the elastic properties and damage behavior of the rocks. This facilitated modeling the stability of the deep boreholes by two different formulations of damage rheology: a dynamic-oriented formulation used to model deformation immediately after the creation of the open hole and a quasi-static formulation used to model longer stress corrosion regime. The calibrated modeling results indicate greater stability with Zenifim arkose than the crystalline granite for deep borehole conditions despite the granite having a greater triaxial compressive strength. Dissipation associated with dilation and porous compaction in the arkose during deformation plays a significant stabilizing role in the borehole compared to crystalline rocks. These results suggest that common strength-based borehole stability assessment may lead to inaccurate predictions. Three-dimensional modeling of bottom-hole stress conditions and the effects of transient borehole geometry show conventional two-dimensional analysis may not be conservative when predicting borehole damage.
The stress history of rocks in the subsurface affects their mechanical and petrophysical properties. Rocks can often experience repeated cycles of loading and unloading due to fluid pressure fluctuations, which will lead to different mechanical behavior from static conditions. This is of importance for several geophysical and industrial applications, for example, wastewater injection and reservoir storage wells, which generate repeated stress perturbations. Laboratory experiments were conducted with Castlegate sandstone to observe the effects of different cyclic pressure loading conditions on a common reservoir analogue. Each sample was hydrostatically loaded in a triaxial cell to a low effective confining pressure, and either pore pressure or confining pressure was cycled at different rates over the course of a few weeks. Fluid permeability was measured during initial loading and periodically between stress cycles. Samples that undergo cyclic loading experience significantly more inelastic (nonrecoverable) strain compared to samples tested without cyclic hydrostatic loading. Permeability decreases rapidly for all tests during the first few days of testing, but the decrease and variability of permeability after this depend upon the loading conditions of each test. Cycling conditions do affect the mechanical behavior; the elastic moduli decrease with the increasing loading rate and stress cycling. The degree of volumetric strain induced by stress cycles is the major control on permeability change in the sandstones, with less compaction leading to more variation from measurement to measurement. The data indicate that cyclic loading degrades permeability and porosity more than static conditions over a similar period, but the petrophysical properties are dictated more by the hydrostatic loading rate rather than the total length of time stress cycling is imposed.
Significant costs can be related to losing circulation of drilling fluids in geothermal drilling. This paper is the second of four case studies of geothermal fields operated by Ormat Technologies, directed at forming a comprehensive strategy to characterize and address lost circulation in varying conditions, and examines the geologic context of and common responses to lost circulation in the loosely consolidated, shallow sedimentary reservoir of the Don A. Campbell geothermal field. The Don A. Campbell Geothermal Field is in the SW portion of Gabbs Valley in NV, along the eastern margin of the Central Walker Lane shear zone. The reservoir here is shallow and primarily in the basin fill, which is hydrothermally altered along fault zones. Wells in this reservoir are highly productive (250-315 L/s) with moderate temperatures (120-125 °C) and were drilled to an average depth of ~1500 ft (450 m). Lost circulation is frequently reported beginning at depths of about 800 ft, slightly shallower than the average casing shoe depth of 900- 1000 ft (275-305 m). Reports of lost circulation frequently coincide with drilling through silicified basin fill. Strategies to address lost circulation differ above and below the cased interval; bentonite chips were used at shallow depths and aerated, gelled drilling fluids were used in the production intervals. Further study of this and other areas will contribute to developing a systematic understanding of geologic contextual-informed lost circulation mitigation strategies.
Accurate knowledge of thermophysical properties of rock is vital to develop meaningful models of high level nuclear waste emplacement scenarios. The Israel Atomic Energy Commission is considering storing high level nuclear waste in the Ghareb formation, a porous kerogen bearing chalk. Sandia is supporting this effort with an evolving lab- based geomechanics testing program. We have completed measurements of thermal properties up to 275C and room temperature hydrostatic compaction measurements. We report thermal conductivity, thermal diffusivity, specific heat, and mass loss from our thermal measurements, and we report bulk moduli and porosity loss from our compaction measurements. These values are crucial for the numerical models to simulate heat transfer and formation compressibility around a heat generating repository.
Large-scale integration of energy storage on the electric grid will be essential to enabling greater penetration of intermittent renewable energy sources, modernizing the grid for increased flexibility security, reliability, and resilience, and enabling cleaner forms of transportation. The purpose of this report is to summarize Sandia's research and capabilities in energy storage and to provide a preliminary roadmap for future efforts in this area that can address the ongoing program needs of DOE and the nation. Mission and vision statements are first presented followed by an overview of the organizational structure at Sandia that provides support and activities in energy storage. Then, a summary of Sandia's energy storage capabilities is presented by technology, including battery storage and materials, power conversion and electronics, subsurface-based energy storage, thermal/thermochemical energy storage, hydrogen storage, data analytics/systems optimization/controls, safety of energy storage systems, and testing/demonstrations/model validation. A summary of identified gaps and needs is also presented for each technology and capability.
To increase understanding of damage associated with underground explosions, a field test program was developed jointly by Sandia and Pacific Northwest National Laboratories at the EMRTC test range in Socorro, NM. The Blue Canyon Dome test site is underlain by a rhyolite that is fractured in places. The test system included deployment of a defined array of 64 probes in eight monitoring boreholes. The monitoring boreholes radially surround a central near vertical shot hole at horizontal distances of 4.6m and 7.6m in cardinal and 45 degrees offset to cardinal directions, respectively. The probes are potted in coarse sand which touches/accesses the rhyolite and are individually accessed via nylon tubing and isolated from each other by epoxy and grout sequences. Pre and post chemical explosion air flow rate measurements, conducted for ~30-45 minutes from each probe, were observed for potential change. The gas flow measurement is a function of the rock mass permeability near a probe. Much of the flow rate change is at depth station 8 (59.4m) and is in the SE quadrant. Flow rate changes are inferred to be caused by the chemical explosion which may have opened pre-existing fractures, fractured the rock and/or caused block displacements by rotations and translations. The air flow rate data acquired here may enable a relationship and/or calibration to rock damage to be developed.
This report documents additional evaluations of Thermal Shock-Resistant Cement (TSRC) developed by Brookhaven National Laboratory (BNL). Our work focused on thermal expansion, and fluid flow through the TSRC, and the application of thermal shock to a steel/TSRC sheathed sample. The key contributions of this work to the geothermal community are: 1) Development of a test system to make measurements of material properties at elevated temperature and pressure. 2) Measurements of thermal expansion and permeability of TSRC at elevated temperature and pressure conditions relevant to in situ geothermal conditions. 3) Development of a test system to thermally shock a steel/TSRC sheathed sample at elevated temperature and pressure conditions relevant to in situ geothermal conditions. Herein we report the results of the study of repeated testing upon 3 cylindrical samples supplied by BNL, one steel, one TSRC, and one steel/TSRC sheathed sample.
Geogenic noble gases are contained in crustal rocks at inter- and intracrystalline sites. In this study, bedded rock salt from southern New Mexico was deformed in a variety of triaxial compression states while measuring the release of naturally contained helium and argon utilizing mass spectrometry. Noble gas release is empirically correlated to volumetric strain and acoustic emissions. At low confining pressures, rock salt deforms primarily by microfracturing, rupturing crystal grains, and releasing helium and argon with a large amount of acoustic emissions, both measured real-time. At higher confining pressure, microfracturing is reduced and the rock salt is presumed to deform more by intracrystalline flow, releasing less amounts of noble gases with fewer acoustic emissions. Our work implies that geogenic gas release during deformation may provide an additional signal which contains information on the type and amount of deformation occurring in a variety of earth systems.
Mining rock salt results in subsurface damage, which may affect the strength because of applied stress, anisotropy, and deformation rate. In this study, we used a Kolsky compression bar to measure the high strain rate response of bedded and domal salt at strain rates up to approximately 50 s−1 in parallel and perpendicular directions to bedding or foliation direction depending on rock salt type. Both types of salt exhibited a negative strain rate effect wherein a decrease in strength was observed with increasing strain rate compared to strength measured in the quasi-static regime. Both materials exhibited strength anisotropy. Fracturing and microfracturing were the dominant deformation mechanisms. High pore pressures and frictional heating due to the high loading rate may have contributed to reduction in strength.
Granular salt is likely to be used as backfill material and a seal system component within geologic salt formations serving as a repository for long-term isolation of nuclear waste. Pressure from closure of the surrounding salt formation will promote consolidation of granular salt, eventually resulting in properties comparable to native salt. Understanding dependence of consolidation processes on stress state, moisture availability, temperature, and time is important for demonstrating sealing functions and long-term repository performance. This study characterizes laboratory-consolidated granular salt by means of microstructural observations. Granular salt material from mining operations was obtained from the bedded Salado Formation hosting the Waste Isolation Pilot Plant and the Avery Island salt dome. Laboratory test conditions included hydrostatic consolidation of jacketed granular salt with varying conditions of confining isochoric stress to 38 MPa, temperature to 250 °C, moisture additions of 1% by weight, time duration, and vented and non-vented states. Resultant porosities ranged between 1% and 22%. Optical and scanning electron microscopic techniques were used to ascertain consolidation mechanisms. From these investigations, samples with 1% added moisture or unvented during consolidation, exhibit clear pressure solution processes with tightly cohered grain boundaries and occluded fluid pores. Samples with only natural moisture content consolidated by a combination of brittle, cataclastic, and crystal plastic deformation. Recrystallization at 250 °C irrespective of moisture conditions was also observed. The range and variability of conditions applied in this study, combined with the techniques used to display microstructural features, are unique, and provide insight into an important area of governing deformation mechanism(s) occurring within salt repository applications.
The Kaiser effect is a stress memory phenomenon which has most often been demonstrated in rock using acoustic emissions. During cyclic loading–unloading–reloading, the acoustic emissions are near zero until the load exceeds the level of the previous load cycle. Researchers explore the Kaiser effect in rock using real-time noble gas release. Laboratory studies using real-time mass spectrometry measurements during deformation have quantified, to a degree, the types of gases released, degree, the types of gases released (Bauer et al. 2016a, b), their release rates and amounts during deformation, estimates of permeability created from pore structure modifications during deformation and the impact of mineral plasticity upon gas release. Its observed that noble gases contained in brittle crystalline rock are readily released during deformation.
We generate a wide range of models of proppant-packed fractures using discrete element simulations, and measure fracture conductivity using finite element flow simulations. This allows for a controlled computational study of proppant structure and its relationship to fracture conductivity and stress in the proppant pack. For homogeneous multi-layered packings, we observe the expected increase in fracture conductivity with increasing fracture aperture, while the stress on the proppant pack remains nearly constant. This is consistent with the expected behavior in conventional proppant-packed fractures, but the present work offers a novel quantitative analysis with an explicit geometric representation of the proppant particles. In single-layered packings (i.e. proppant monolayers), there is a drastic increase in fracture conductivity as the proppant volume fraction decreases and open flow channels form. However, this also corresponds to a sharp increase in the mechanical stress on the proppant pack, as measured by the maximum normal stress relative to the side crushing strength of typical proppant particles. We also generate a variety of computational geometries that resemble highly heterogeneous proppant packings hypothesized to form during channel fracturing. In some cases, these heterogeneous packings show drastic improvements in conductivity with only moderate increase in the stress on the proppant particles, suggesting that in certain applications these structures are indeed optimal. We also compare our computer-generated structures to micro computed tomography imaging of a manually fractured laboratory-scale shale specimen, and find reasonable agreement in the geometric characteristics.
We use helium released during mechanical deformation of shales as a signal to explore the effects of deformation and failure on material transport properties. A dynamic dual-permeability model with evolving pore and fracture networks is used to simulate gases released from shale during deformation and failure. Changes in material properties required to reproduce experimentally observed gas signals are explored. We model two different experiments of 4He flow rate measured from shale undergoing mechanical deformation, a core parallel to bedding and a core perpendicular to bedding. We find that the helium signal is sensitive to fracture development and evolution as well as changes in the matrix transport properties. We constrain the timing and effective fracture aperture, as well as the increase in matrix porosity and permeability. Increases in matrix permeability are required to explain gas flow prior to macroscopic failure, and the short-term gas flow postfailure. Increased matrix porosity is required to match the long-term, postfailure gas flow. Our model provides the first quantitative interpretation of helium release as a result of mechanical deformation. The sensitivity of this model to changes in the fracture network, as well as to matrix properties during deformation, indicates that helium release can be used as a quantitative tool to evaluate the state of stress and strain in earth materials.
The objectives and purpose of this research has been to produce laboratory-based experimental and numerical analyses to provide a physics-based understanding of shear stimulation phenomena (hydroshearing) and its evolution during stimulation. Water was flowed along fractures in hot and stressed fractured rock, to promote slip. The controlled laboratory experiments provide a high resolution/high quality data resource for evaluation of analysis methods developed by DOE to assess EGS “behavior” during this stimulation process. Segments of the experimental program will provide data sets for model input parameters, i.e., material properties, and other segments of the experimental program will represent small scale physical models of an EGS system, which may be modeled. The coupled lab/analysis project has been a study of the response of a fracture in hot, water-saturated fractured rock to shear stress experiencing fluid flow. Under this condition, the fracture experiences a combination of potential pore pressure changes and fracture surface cooling, resulting in slip along the fracture. The laboratory work provides a means to assess the role of “hydroshearing” on permeability enhancement in reservoir stimulation. Using the laboratory experiments and results to define boundary and input/output conditions of pore pressure, thermal stress, fracture shear deformation and fluid flow, and models were developed and simulations completed by the University of Oklahoma team. The analysis methods are ones used on field scale problems. The sophisticated numerical models developed contain parameters present in the field. The analysis results provide insight into the role of fracture slip on permeability enhancement-“hydroshear” is to be obtained. The work will provide valuable input data to evaluate stimulation models, thus helping design effective EGS.
Radiogenic noble gases are contained in crustal rock at inter and intra granular sites. The gas composition depends on lithology, geologic history, fluid phases, and the aging effect by decay of U, Th, and K. The isotopic signature of noble gases found in rocks is vastly different than that of the atmosphere which is contributed by a variety of sources. When rock is subjected to stress conditions exceeding about half its yield strength, micro-cracks begin to form. As rock deformation progresses a fracture network evolves, releasing trapped noble gases and changing the transport properties to gas migration. Thus, changes in gas emanation and noble gas composition from rocks could be used to infer changes in stress-state and deformation. The purpose of this study has been to evaluate the effect of deformation/strain rate upon noble gas release. Four triaxial experiments were attempted for a strain rate range of %7E10-8 /s (180,000s) to %7E 10-4/s (500s); the three fully successful experiments (at the faster strain rates) imply the following: (1) helium is measurably released for all strain rates during deformation, this release is in amounts 1-2 orders of magnitude greater than that present in the air, and (2) helium gas release increases with decreasing strain rate.
An experimental system we developed combines triaxial rock deformation and mass spectrometry to measure noble gas flow before, during, and after rock fracture. Geogenic noble gas is released during triaxial deformation (real time) and is related to volume strain and acoustic emissions. The noble gas release then represents a signal of deformation during its stages of development. Noble gases are contained in most crustal rock at inter and intra granular sites. Their release during natural and man-made stress and strain changes represents a signal of deformation in brittle and semi-brittle conditions. The noble gas composition depends on lithology, geologic history, age of the rock, and fluids present. Uranium, thorium and potassium-40 concentrations in the rocks also affect the production of radiogenic noble gases (4He, Ar). Noble gas emission and its relationship to crustal processes have been studied for many years in the geologic community including correlations to tectonic velocities and qualitative estimates of deep permeability from surface measurements, finger prints of nuclear weapon detonation, and as a potential precursory signal to earthquakes attributed to gas release due to pre-seismic stress, dilatancy and/or fracturing of the rock. Helium emission has been shown as a precursor of volcanic activity. We present empirical results/relationships of specimen strain, microstructural evolution, acoustic emissions, and noble gas release from laboratory triaxial experiments performed upon a granite and a young basalt, bedded salt, and a marine shale.
A series of constant mean stress (CMS) and constant shear stress (CSS) tests were performed to investigate the evolution of permeability and Biot coefficient at high mean stresses in a high porosity reservoir analog (Castlegate sandstone). Permeability decreases as expected with increasing mean stress, from about 20 Darcy at the beginning of the tests to between 1.5 and 0.3 Darcy at the end of the tests (mean stresses up to 275 MPa). The application of shear stress causes permeability to drop below that of a hydrostatic test at the same mean stress. Results show a nearly constant rate decrease in the Biot coefficient as the mean stress increases during hydrostatic loading, and as the shear stress increases during CMS loading. CSS tests show a stabilization of the Biot coefficient after the application of shear stress.
This paper presents a 3D finite element model for simulating shear slip on fractures in rock in response to coupled thermo-poro-mechanical processes. The modeling is part of a broader effort to investigate the role of pore pressure and cooling by cold water injection on shear slip and permeability increase in granitic rock using laboratory shearing experiments under triaxial conditions. In particular, 3D thermo-poro-mechanical finite element modeling and analysis of injection experiment in fractured rock has been carried out to analyze the role of pore pressure, temperature, fracture deformation and their interactions. 4-noded tetrahedral elements are employed for intact rock deformation and transport processes within the matrix. To represent the mechanical response of a fracture surface, zero thickness contact interface element is developed based on recently developed element partitioning algorithm and procedures for applying hydraulic pressure on the fracture surfaces. A Mohr-Coulomb type criterion is adapted to capture the slip on the fracture and to quantify its reversible and irreversible deformation. The numerical model has been calibrated using results from well controlled, advanced laboratory experiments. Excellent agreement between modeling and experimental observations is achieved. Simulation results illustrate that pore pressure increase and rock matrix/fracture surface cooling cause the fracture system to deform and slip. Fracture slip is promoted due to its normal stress reduction associated with cooling effect of cold fluid injection. The numerical model provides a physics-based understanding of the role of coupled processes on shear stimulation phenomenon and the resulting permeability enhancement.
Natural gas storage facilities are a critical component of our energy supply and distribution chain, allowing elasticity in gas supply to accommodate daily to seasonal demand fluctuations. As has been made evident by the recent Aliso Canyon Gas Storage facility incident, a loss of well integrity may result in significant consequences, including the prolonged shutdown of an entire facility. The Aliso Canyon gas well blowout emitted approximately 100,000 tonnes of natural gas (mostly methane) over 4 months and displaced thousands of nearby residents from their homes. The high visibility of the event has led to increased scrutiny of the safety of natural gas storage at the Aliso Canyon facility, led to questions about energy reliability, and raised broader concerns for natural gas storage integrity throughout the country.
Deep Borehole Disposal (DBD) of high-level radioactive wastes has been considered an option for geological isolation for many years (Hess et al. 1957). Recent advances in drilling technology have decreased costs and increased reliability for large-diameter (i.e., ≥50 cm [19.7”]) boreholes to depths of several kilometers (Beswick 2008; Beswick et al. 2014). These advances have therefore also increased the feasibility of the DBD concept (Brady et al. 2009; Cornwall 2015), and the current field test design will demonstrate the DBD concept and these advances. The US Department of Energy (DOE) Strategy for the Management and Disposal of Used Nuclear Fuel and High-Level Radioactive Waste (DOE 2013) specifically recommended developing a research and development plan for DBD. DOE sought input or expression of interest from States, local communities, individuals, private groups, academia, or any other stakeholders willing to host a Deep Borehole Field Test (DBFT). The DBFT includes drilling two boreholes nominally 200m [656’] apart to approximately 5 km [16,400’] total depth, in a region where crystalline basement is expected to begin at less than 2 km depth [6,560’]. The characterization borehole (CB) is the smaller-diameter borehole (i.e., 21.6 cm [8.5”] diameter at total depth), and will be drilled first. The geologic, hydrogeologic, geochemical, geomechanical and thermal testing will take place in the CB. The field test borehole (FTB) is the larger-diameter borehole (i.e., 43.2 cm [17”] diameter at total depth). Surface handling and borehole emplacement of test package will be demonstrated using the FTB to evaluate engineering feasibility and safety of disposal operations (SNL 2016).
The 2015-2016 Aliso Canyon/Porter Ranch natural gas well blowout emitted approximately 100,000 tonnes of natural gas (mostly methane, CH4) over four months. The blowout impacted thousands of nearby residents, who were displaced from their homes. The high visibility of the event has led to increased scrutiny of the safety of natural gas storage at the Aliso Canyon facility, as well as broader concern for natural gas storage integrity throughout the country. This report presents the findings of the DOE National Laboratories Well Integrity Work Group efforts in the four tasks. In addition to documenting the work of the Work Group, this report presents high priority recommendations to improve well integrity and reduce the likelihood and consequences of subsurface natural gas leaks.
The recent boom in the oil and natural gas industry of hydraulic fracture of source rocks has caused a new era in oil and gas production worldwide. However, there are many parts of this process that are poorly understood and thus hard to control. One of the few things that can be controlled is the process of injection to create the fractures in the subsurface and the subsequent injection of proppants to maintain the permeability of the fractured formation, allowing hydrocarbons to be extracted. The goal of this work was to better understand the injection process and resulting proppant distribution in the fracture through a combination of lab-scale experiments and computational models.
This work describes initial experimental results of helium tracer release monitoring during deformation of shale. Naturally occurring radiogenic 4He is present in high concentration in most shales. During rock deformation, accumulated helium could be released as fractures are created and new transport pathways are created. We present the results of an experimental study in which confined reservoir shale samples, cored parallel and perpendicular to bedding, which were initially saturated with helium to simulate reservoir conditions, are subjected to triaxial compressive deformation. During the deformation experiment, differential stress, axial, and radial strains are systematically tracked. Release of helium is dynamically measured using a helium mass spectrometer leak detector. Helium released during deformation is observable at the laboratory scale and the release is tightly coupled to the shale deformation. These first measurements of dynamic helium release from rocks undergoing deformation show that helium provides information on the evolution of microstructure as a function of changes in stress and strain.
The Mount Simon Sandstone and Eau Claire Formation represent a potential reservoir-caprock system for wastewater disposal, geologic CO2 storage, and compressed air energy storage (CAES) in the Midwestern United States. A primary concern to site performance is heterogeneity in rock properties that could lead to nonideal injectivity and distribution of injected fluids (e.g., poor sweep efficiency). Using core samples from the Dallas Center domal structure, Iowa, we investigate pore characteristics that govern flow properties of major lithofacies of these formations. Methods include gas porosimetry and permeametry, mercury intrusion porosimetry, thin section petrography, and X-ray diffraction. The lithofacies exhibit highly variable intraformational and interformational distributions of pore throat and body sizes. Based on pore-throat size, there are four distinct sample groups. Micropore-throat-dominated samples are from the Eau Claire Formation, whereas the macropore-dominated, mesopore-dominated, and uniform-dominated samples are from the Mount Simon Sandstone. Complex paragenesis governs the high degree of pore and pore-throat size heterogeneity, due to an interplay of precipitation, nonuniform compaction, and later dissolution of cements. The cement dissolution event probably accounts for much of the current porosity in the unit. Mercury intrusion porosimetry data demonstrate that the heterogeneous nature of the pore networks in the Mount Simon Sandstone results in a greater than normal opportunity for reservoir capillary trapping of nonwetting fluids, as quantified by CO2 and air column heights that vary over three orders of magnitude, which should be taken into account when assessing the potential of the reservoir-caprock system for waste disposal (CO2 or produced water) and resource storage (natural gas and compressed air). Our study quantitatively demonstrates the significant impact of millimeter-scale to micron-scale porosity heterogeneity on flow and transport in reservoir sandstones.
Performing experiments in the laboratory that mimic conditions in the field is challenging. In an attempt to understand hydraulic fracture in the field, and provide laboratory flow results for model verification, an effort to duplicate the typical fracture pattern for long horizontal wells has been made. The typical "disks on a string" fracture formation is caused by properly orienting the long horizontal well such that it is parallel to the minimum principal stress direction, then fracturing the rock. In order to replicate this feature in the laboratory with a traditional cylindrical specimen the test must be performed under extensile stress conditions and the specimen must have been cored parallel to bedding in order to avoid failure along a bedding plane, and replicate bedding orientation in the field. Testing has shown that it is possible to form failure features of this type in the laboratory. A novel method for jacketing is employed to allow fluid to flow out of the fracture and leave the specimen without risking the integrity of the jacket; this allows proppant to be injected into the fracture, simulating loss of fracturing fluids to the formation, and allowing a solid proppant pack to be developed.
Performing experiments in the laboratory that mimic conditions in the field is challenging. In an attempt to understand hydraulic fracture in the field, and provide laboratory flow results for model verification, an effort to duplicate the typical fracture pattern for long horizontal wells has been made. The typical "disks on a string" fracture formation is caused by properly orienting the long horizontal well such that it is parallel to the minimum principal stress direction, then fracturing the rock. In order to replicate this feature in the laboratory with a traditional cylindrical specimen the test must be performed under extensile stress conditions and the specimen must have been cored parallel to bedding in order to avoid failure along a bedding plane, and replicate bedding orientation in the field. Testing has shown that it is possible to form failure features of this type in the laboratory. A novel method for jacketing is employed to allow fluid to flow out of the fracture and leave the specimen without risking the integrity of the jacket; this allows proppant to be injected into the fracture, simulating loss of fracturing fluids to the formation, and allowing a solid proppant pack to be developed.
Seven water-saturated triaxial extension experiments were conducted on four sedimentary rocks. This experimental condition was hypothesized more representative of that existing for downhole hydrofracture and thus it may improve our understanding of the phenomena. In all tests the pore pressure was 10 MPa and confirming pressure was adjusted to achieve tensile and transitional failure mode conditions. Using previous work in this LDRD for comparison, the law of effective stress is demonstrated in extension using this sample geometry. In three of the four lithologies, no apparent chemo-mechanical effect of water is apparent, and in the fourth lithology test results indicate some chemo-mechanical effect of water.
The thermal properties of halite have broad practical importance, from design and long-term modeling of nuclear waste repositories to analysis and performance assessment of underground natural gas, petroleum and air storage facilities. Using a computer-controlled transient plane source method, single-crystal halite thermal conductivity, thermal diffusivity and specific heat were measured from -75°C to 300°C. These measurements reproduce historical high-temperature experiments and extend the lower temperature extreme into cryogenic conditions. Measurements were taken in 25-degree increments from -75°C to 300°C. Over this temperature range, thermal conductivity decreases by a factor of 3.7, from 9.975 to 2.699 W/mK , and thermal diffusivity decreases by a factor of 3.6, from 5.032 to 1.396 mm²/s. Specific heat does not appear to be temperature dependent, remaining near 2.0 MJ/m³K at all temperatures. This work is intended to develop and expand the existing dataset of halite thermal properties, which are of particular value in defining the parameters of salt storage thermophysical models. The work was motivated by a need for thermal conductivity values in a mixture theory model used to determine bulk thermal conductivity of reconsolidating crushed salt.
This report presents efforts to develop the use of in situ naturally-occurring noble gas tracers to evaluate transport mechanisms and deformation in shale hydrocarbon reservoirs. Noble gases are promising as shale reservoir diagnostic tools due to their sensitivity of transport to: shale pore structure; phase partitioning between groundwater, liquid, and gaseous hydrocarbons; and deformation from hydraulic fracturing. Approximately 1.5-year time-series of wellhead fluid samples were collected from two hydraulically-fractured wells. The noble gas compositions and isotopes suggest a strong signature of atmospheric contribution to the noble gases that mix with deep, old reservoir fluids. Complex mixing and transport of fracturing fluid and reservoir fluids occurs during production. Real-time laboratory measurements were performed on triaxially-deforming shale samples to link deformation behavior, transport, and gas tracer signatures. Finally, we present improved methods for production forecasts that borrow statistical strength from production data of nearby wells to reduce uncertainty in the forecasts.
A helium leakage detection system was modified to measure gas permeability on extracted cores of nearly impermeable rock. Here we use a Helium - Mass - Spectrometry - Permeameter (HMSP) to conduct a constant pressure, steady state flow test through a sample using helium gas. Under triaxial stress conditions, the HMSP can measure flow and estimate permeability of rocks and geomaterials down to the nanodarcy scale (10-21 m2). In this study, measurements of flow through eight shale samples under hydrostatic conditions were in the range of 10-7 to 10-9 Darcy. We extend this flow measurement technology by dynamically monitoring the release of helium from a helium saturated shale sample during a triaxial deformation experiment. The helium flow, initially extremely low, consistent with the low permeability of shale, is observed to increase in advance of volume strain increase during deformation of the shale. This is perhaps the result of microfracture development and flow path linkage through the microfractures within the shale. Once microfracturing coalescence initiates, there is a large increase in helium release and flow. This flow rate increase is likely the result of development of a macrofracture in the sample, a flow conduit, later confirmed by post-test observations of the deformed sample. The release rate (flow) peaks and then diminishes slightly during subsequent deformation; however the post deformation flow rate is considerably greater than that of undeformed shale.
A laboratory testing program was developed to examine the short-term mechanical and time-dependent (creep) behavior of salt from the Bayou Choctaw Salt Dome. Core was tested under creep and quasi-static constant mean stress axisymmetric compression, and constant mean stress axisymmetric extension conditions. Creep tests were performed at 38 degrees Celsius, and the axisymmetric tests were performed at ambient temperatures (22-26 degrees Celsius). The testing performed indicates that the dilation criterion is pressure and stress state dependent. It was found that as the mean stress increases, the shear stress required to cause dilation increases. The results for this salt are reasonably consistent with those observed for other domal salts. Also it was observed that tests performed under extensile conditions required consistently lower shear stress to cause dilation for the same mean stress, which is consistent with other domal salts. Young's modulus ranged from 27.2 to 58.7 GPa with an average of 44.4 GPa, with Poisson's ratio ranging from 0.10 to 0.43 with an average of 0.30. Creep testing indicates that the BC salt is intermediate in creep resistance when compared with other bedded and domal salt steady-state behavior.
A helium leakage detection system was modified to measure gas permeability on extracted cores of nearly impermeable rock. Here we use a Helium - Mass - Spectrometry - Permeameter (HMSP) to conduct a constant pressure, steady state flow test through a sample using helium gas. Under triaxial stress conditions, the HMSP can measure flow and estimate permeability of rocks and geomaterials down to the nanodarcy scale (10-21 m2). In this study, measurements of flow through eight shale samples under hydrostatic conditions were in the range of 10-7 to 10-9 Darcy. We extend this flow measurement technology by dynamically monitoring the release of helium from a helium saturated shale sample during a triaxial deformation experiment. The helium flow, initially extremely low, consistent with the low permeability of shale, is observed to increase in advance of volume strain increase during deformation of the shale. This is perhaps the result of microfracture development and flow path linkage through the microfractures within the shale. Once microfracturing coalescence initiates, there is a large increase in helium release and flow. This flow rate increase is likely the result of development of a macrofracture in the sample, a flow conduit, later confirmed by post-test observations of the deformed sample. The release rate (flow) peaks and then diminishes slightly during subsequent deformation; however the post deformation flow rate is considerably greater than that of undeformed shale.
The sedimentologic and tectonic histories of clastic cap rocks and their inherent mechanical properties control the nature of permeable fractures within them. The migration of fluid through mm- to cm-scale fracture networks can result in focused fluid flow allowing hydrocarbon production from unconventional reservoirs or compromising the seal integrity of fluid traps. To understand the nature and distribution of subsurface fluid-flow pathways through fracture networks in cap-rock seals we examine four exhumed Paleozoic and Mesozoic seal analogs in Utah. We combine these outcrop analyses with subsidence analysis, paleoloading histories, and rock-strength testing data in modified Mohr-Coulomb-Griffith analyses to evaluate the effects of differential stress and rock type on fracture mode. Relative to the underlying sandstone reservoirs, all four seal types are low-permeability, heterolithic sequences that show mineralized hydraulic-extension fractures, extensional-shear fractures, and shear fractures. Burial-history models suggest that the cap-rock seal analogs reached a maximum burial depth >4 km (2.5 mi) and experienced a lithostatic load of up to 110 MPa (15,954 psi). Median tensile strength from indirect mechanical tests ranges from 2.3 MPa (334 psi) in siltstone to 11.5 MPa (1668 psi) in calcareous shale. Analysis of the pore-fluid factor (λv = Pf/σv) through time shows changes in the expected failure mode (extensional shear or hydraulic extension), and that failure mode depends on a combination of mechanical rock properties and differential stress. As expected with increasing lithostatic load, the amount of overpressure that is required to induce failure increases but is also lithology dependent.
Reconsolidated crushed salt is being considered as a backfilling material placed upon nuclear waste within a salt repository environment. In-depth knowledge of thermal and mechanical properties of the crushed salt as it reconsolidates is critical to thermal/mechanical modeling of the reconsolidation process. An experimental study was completed to quantitatively evaluate the thermal conductivity of reconsolidated crushed salt as a function of porosity and temperature. The crushed salt for this study came from the Waste Isolation Pilot Plant (WIPP). In this work the thermal conductivity of crushed salt with porosity ranging from 1% to 40% was determined from room temperature up to 300°C, using two different experimental methods. Thermal properties (including thermal conductivity, thermal diffusivity and specific heat) of single-crystal salt were determined for the same temperature range. The salt was observed to dewater during heating; weight loss from the dewatering was quantified. The thermal conductivity of reconsolidated crushed salt decreases with increasing porosity; conversely, thermal conductivity increases as the salt consolidates. The thermal conductivity of reconsolidated crushed salt for a given porosity decreases with increasing temperature. A simple mixture theory model is presented to predict and compare to the data developed in this study.
We are developing computational models to elucidate the expansion and dynamic filling process of a polyurethane foam, PMDI. The polyurethane of interest is chemically blown, where carbon dioxide is produced via the reaction of water, the blowing agent, and isocyanate. The isocyanate also reacts with polyol in a competing reaction, which produces the polymer. Here we detail the experiments needed to populate a processing model and provide parameters for the model based on these experiments. The model entails solving the conservation equations, including the equations of motion, an energy balance, and two rate equations for the polymerization and foaming reactions, following a simplified mathematical formalism that decouples these two reactions. Parameters for the polymerization kinetics model are reported based on infrared spectrophotometry. Parameters describing the gas generating reaction are reported based on measurements of volume, temperature and pressure evolution with time. A foam rheology model is proposed and parameters determined through steady-shear and oscillatory tests. Heat of reaction and heat capacity are determined through differential scanning calorimetry. Thermal conductivity of the foam as a function of density is measured using a transient method based on the theory of the transient plane source technique. Finally, density variations of the resulting solid foam in several simple geometries are directly measured by sectioning and sampling mass, as well as through x-ray computed tomography. These density measurements will be useful for model validation once the complete model is implemented in an engineering code.
Accurate knowledge of thermophysical properties of urethane foam is considered extremely important for meaningful models and analyses to be developed of scenarios wherein the foam is heated. Its performance at temperature requires a solid understanding of the foam material properties at temperature. Also, foam properties vary with density/porosity. An experimental program to determine the thermal properties of the two foams and their parent solid urethane was developed in order to support development of a predictive model relating density and thermal properties from first principles. Thermal properties (thermal conductivity, diffusivity, and specific heat) of the foam were found to vary with temperatures from 26°C to 90°C. Thermal conductivity generally increases with increasing temperature for a given initial density and ranges from .0433 W/mK at 26°C to .0811 W/mK at 90°C; thermal diffusivity generally decreases with increasing temperature for a given initial density and ranges from .4101 mm2/s at 26°C to .1263 mm2/s at 90°C; and specific heat generally increases with increasing temperature for a given initial density and ranges from .1078 MJ/m3K at 26°C to .6323 MJ/m3K at 90°C. Thermal properties of the solid urethane were also found to vary with temperatures from 26°C to 90°C. Average thermal conductivity generally increases with increasing temperature for a given initial density and ranges from 0.126 to 0.131 W/mK at 26°C to 0.153 to 0.157 W/mK at 90°C; average thermal diffusivity generally decreases with increasing temperature for a given initial density and ranges from 0.142 to 0.147 mm2/s at 26°C to 0.124 to 0.125 mm2/s at 90°C; and average specific heat generally increases with increasing temperature for a given initial density and ranges from 0.889 to 0.899 MJ/m3K to 1.229 to 1.274 MJ/m3K at 90°C. The density of both foam and solid urethane decreased with increasing temperature.
A laboratory testing program was developed to examine the short-term mechanical and time-dependent (creep) behavior of salt from the Bayou Choctaw Salt Dome. This report documents the test methodologies, and constitutive properties inferred from tests performed. These are used to extend our understanding of the mechanical behavior of the Bayou Choctaw domal salt and provide a data set for numerical analyses. The resulting information will be used to support numerical analyses of the current state of the Bayou Choctaw Dome as it relates to its crude oil storage function as part of the US Strategic Petroleum Reserve. Core obtained from Drill Hole BC-102B was tested under creep and quasi-static constant mean stress axisymmetric compression, and constant mean stress axisymmetric extension conditions. Creep tests were performed at 100 degrees Fahrenheit, and the axisymmetric tests were performed at ambient temperatures (72-78 degrees Fahrenheit). The testing performed indicates that the dilation criterion is pressure and stress state dependent. It was found that as the mean stress increases, the shear stress required to cause dilation increases. The results for this salt are reasonably consistent with those observed for other domal salts. Also it was observed that tests performed under extensile conditions required consistently lower shear stress to cause dilation for the same mean stress, which is consistent with other domal salts. Young's moduli ranged from 3.95 x 106 to 8.51 x 106 psi with an average of 6.44 x 106 psi, with Poisson's ratios ranging from 0.10 to 0.43 with an average of 0.30. Creep testing indicates that the BC salt is intermediate in creep resistance when compared with other bedded and domal salt steady-state behavior.
Accurate knowledge of thermophysical properties of concrete is considered extremely important for meaningful models to be developed of scenarios wherein the concrete is rapidly heated. Test of solid propellant burns on samples of concrete from Launch Complex 17 of the Cape Canaveral show spallation and fragmentation. In response to the need for accurate modeling scenarios of these observations, an experimental program to determine the permeability and thermal properties of the concrete was developed. Room temperature gas permeability measurements of Launch Complex 17 of the Cape Canaveral concrete dried at 50°C yield permeability estimates of 0.07mD (mean), and thermal properties (thermal conductivity, diffusivity, and specific heat) were found to vary with temperatures from room temperature to 300°C. Thermal conductivity ranges from 1.7-1.9 W/mK at 50°C to 1.0-1.15 W/mK at 300°C, thermal diffusivity ranges from 0.75-0.96 mm2/s at 50°C to 0.44-0.58 mm2/s at 300°C, and specific heat ranges from 1.76-2.32 /m3K to 2.00-2.50 /m3K at 300°C.
The Iowa Stored Energy Plant Agency selected a geologic structure at Dallas Center, Iowa, for evaluation of subsurface compressed air energy storage. The site was rejected due to lower-than-expected and heterogeneous permeability of the target reservoir, lower-than-desired porosity, and small reservoir volume. In an initial feasibility study, permeability and porosity distributions of flow units for the nearby Redfield gas storage field were applied as analogue values for numerical modeling of the Dallas Center Structure. These reservoir data, coupled with an optimistic reservoir volume, produced favorable results. However, it was determined that the Dallas Center Structure cannot be simplified to four zones of high, uniform permeabilities. Updated modeling using field and core data for the site provided unfavorable results for air fill-up. This report presents Sandia National Laboratories' petrologic and petrophysical analysis of the Dallas Center Structure that aids in understanding why the site was not suitable for gas storage.
Southwest Solar Technologies Inc. is constructing a Solar-Fuel Hybrid Turbine energy system. This innovative energy system combines solar thermal energy with compressed air energy storage and natural gas fuel backup capability to provide firm, non-intermittent power. In addition, the energy system will have very little impact on the environment since, unlike other Concentrated Solar Power (CSP) technologies, it requires minimal water. In 2008 Southwest Solar Technologies received a Solar America Showcase award from the Department of Energy for Technical Assistance from Sandia National Laboratories. This report details the work performed as part of the Solar America Showcase award for Southwest Solar Technologies. After many meetings and visits between Sandia National Labs and Southwest Solar Technologies, several tasks were identified as part of the Technical Assistance and the analysis and results for these are included here.
A reference design and operational procedures for the disposal of high-level radioactive waste in deep boreholes have been developed and documented. The design and operations are feasible with currently available technology and meet existing safety and anticipated regulatory requirements. Objectives of the reference design include providing a baseline for more detailed technical analyses of system performance and serving as a basis for comparing design alternatives. Numerous factors suggest that deep borehole disposal of high-level radioactive waste is inherently safe. Several lines of evidence indicate that groundwater at depths of several kilometers in continental crystalline basement rocks has long residence times and low velocity. High salinity fluids have limited potential for vertical flow because of density stratification and prevent colloidal transport of radionuclides. Geochemically reducing conditions in the deep subsurface limit the solubility and enhance the retardation of key radionuclides. A non-technical advantage that the deep borehole concept may offer over a repository concept is that of facilitating incremental construction and loading at multiple perhaps regional locations. The disposal borehole would be drilled to a depth of 5,000 m using a telescoping design and would be logged and tested prior to waste emplacement. Waste canisters would be constructed of carbon steel, sealed by welds, and connected into canister strings with high-strength connections. Waste canister strings of about 200 m length would be emplaced in the lower 2,000 m of the fully cased borehole and be separated by bridge and cement plugs. Sealing of the upper part of the borehole would be done with a series of compacted bentonite seals, cement plugs, cement seals, cement plus crushed rock backfill, and bridge plugs. Elements of the reference design meet technical requirements defined in the study. Testing and operational safety assurance requirements are also defined. Overall, the results of the reference design development and the cost analysis support the technical feasibility of the deep borehole disposal concept for high-level radioactive waste.
This report is a preliminary assessment of the ignition and explosion potential in a depleted hydrocarbon reservoir from air cycling associated with compressed air energy storage (CAES) in geologic media. The study identifies issues associated with this phenomenon as well as possible mitigating measures that should be considered. Compressed air energy storage (CAES) in geologic media has been proposed to help supplement renewable energy sources (e.g., wind and solar) by providing a means to store energy when excess energy is available, and to provide an energy source during non-productive or low productivity renewable energy time periods. Presently, salt caverns represent the only proven underground storage used for CAES. Depleted natural gas reservoirs represent another potential underground storage vessel for CAES because they have demonstrated their container function and may have the requisite porosity and permeability; however reservoirs have yet to be demonstrated as a functional/operational storage media for compressed air. Specifically, air introduced into a depleted natural gas reservoir presents a situation where an ignition and explosion potential may exist. This report presents the results of an initial study identifying issues associated with this phenomena as well as possible mitigating measures that should be considered.
CAES in geologic media has been proposed to help 'firm' renewable energy sources (wind and solar) by providing a means to store energy when excess energy was available, and to provide an energy source during non-productive renewable energy time periods. Such a storage media may experience hourly (perhaps small) pressure swings. Salt caverns represent the only proven underground storage used for CAES, but not in a mode where renewable energy sources are supported. Reservoirs, both depleted natural gas and aquifers represent other potential underground storage vessels for CAES, however, neither has yet to be demonstrated as a functional/operational storage media for CAES.
Specimens of poled and unpoled PZST ceramic were tested under hydrostatic loading conditions at temperatures of -55, 25, and 75 C. The objective of this experimental study was to obtain the electro-mechanical properties of the ceramic and the criteria of FE (Ferroelectric) to AFE (Antiferroelectric) phase transformations of the PZST ceramic to aid grain-scale modeling efforts in developing and testing realistic response models for use in simulation codes. As seen in previous studies, the poled ceramic from PZST undergoes anisotropic deformation during the transition from a FE to an AFE phase at -55 C. Warmer temperature tests exhibit anisotropic deformation in both the FE and AFE phase. The phase transformation is permanent at -55 C for all ceramics tests, whereas the transformation can be completely reversed at 25 and 75 C. The change in the phase transformation pressures at different temperatures were practically identical for both unpoled and poled PZST specimens. Bulk modulus for both poled and unpoled material was lowest in the FE phase, intermediate in the transition phase, and highest in the AFE phase. Additionally, bulk modulus varies with temperature in that PZST is stiffer as temperature decreases. Results from one poled-biased test for PZST and four poled-biased tests from PNZT 95/5-2Nb are presented. A bias of 1kV did not show noticeable differences in phase transformation pressure for the PZST material. However, with PNZT 95/5-2Nb phase transformation pressure increased with increasing voltage bias up to 4.5kV.
This report is a revision of SAND2009-0852. SAND2009-0852 was revised because it was discovered that a gage used in the original testing was mis-calibrated. Following the recalibration, all affected raw data were recalculated and re-presented. Most revised data is similar to, but slightly different than, the original data. Following the data re-analysis, none of the inferences or conclusions about the data or site relative to the SAND2009-0852 data have been changed. A laboratory testing program was developed to examine the mechanical behavior of salt from the Richton salt dome. The resulting information is intended for use in design and evaluation of a proposed Strategic Petroleum Reserve storage facility in that dome. Core obtained from the drill hole MRIG-9 was obtained from the Texas Bureau of Economic Geology. Mechanical properties testing included: (1) acoustic velocity wave measurements; (2) indirect tensile strength tests; (3) unconfined compressive strength tests; (4) ambient temperature quasi-static triaxial compression tests to evaluate dilational stress states at confining pressures of 725, 1450, 2175, and 2900 psi; and (5) confined triaxial creep experiments to evaluate the time-dependent behavior of the salt at axial stress differences of 4000 psi, 3500 psi, 3000 psi, 2175 psi and 2000 psi at 55 C and 4000 psi at 35 C, all at a constant confining pressure of 4000 psi. All comments, inferences, discussions of the Richton characterization and analysis are caveated by the small number of tests. Additional core and testing from a deeper well located at the proposed site is planned. The Richton rock salt is generally inhomogeneous as expressed by the density and velocity measurements with depth. In fact, we treated the salt as two populations, one clean and relatively pure (> 98% halite), the other salt with abundant (at times) anhydrite. The density has been related to the insoluble content. The limited mechanical testing completed has allowed us to conclude that the dilatational criteria are distinct for the halite-rich and other salts, and that the dilation criteria are pressure dependent. The indirect tensile strengths and unconfined compressive strengths determined are consistently lower than other coastal domal salts. The steady-state-only creep model being developed suggests that Richton salt is intermediate in creep resistance when compared to other domal and bedded salts. The results of the study provide only limited information for structural modeling needed to evaluate the integrity and safety of the proposed cavern field. This study should be augmented with more extensive testing. This report documents a series of test methods, philosophies, and empirical relationships, etc., that are used to define and extend our understanding of the mechanical behavior of the Richton salt. This understanding could be used in conjunction with planned further studies or on its own for initial assessments.
Preliminary evaluation of deep borehole disposal of high-level radioactive waste and spent nuclear fuel indicates the potential for excellent long-term safety performance at costs competitive with mined repositories. Significant fluid flow through basement rock is prevented, in part, by low permeabilities, poorly connected transport pathways, and overburden self-sealing. Deep fluids also resist vertical movement because they are density stratified. Thermal hydrologic calculations estimate the thermal pulse from emplaced waste to be small (less than 20 C at 10 meters from the borehole, for less than a few hundred years), and to result in maximum total vertical fluid movement of {approx}100 m. Reducing conditions will sharply limit solubilities of most dose-critical radionuclides at depth, and high ionic strengths of deep fluids will prevent colloidal transport. For the bounding analysis of this report, waste is envisioned to be emplaced as fuel assemblies stacked inside drill casing that are lowered, and emplaced using off-the-shelf oilfield and geothermal drilling techniques, into the lower 1-2 km portion of a vertical borehole {approx}45 cm in diameter and 3-5 km deep, followed by borehole sealing. Deep borehole disposal of radioactive waste in the United States would require modifications to the Nuclear Waste Policy Act and to applicable regulatory standards for long-term performance set by the US Environmental Protection Agency (40 CFR part 191) and US Nuclear Regulatory Commission (10 CFR part 60). The performance analysis described here is based on the assumption that long-term standards for deep borehole disposal would be identical in the key regards to those prescribed for existing repositories (40 CFR part 197 and 10 CFR part 63).
A laboratory testing program was developed to examine the mechanical behavior of salt from the Richton salt dome. The resulting information is intended for use in design and evaluation of a proposed Strategic Petroleum Reserve storage facility in that dome. Core obtained from the drill hole MRIG-9 was obtained from the Texas Bureau of Economic Geology. Mechanical properties testing included: (1) acoustic velocity wave measurements; (2) indirect tensile strength tests; (3) unconfined compressive strength tests; (4) ambient temperature quasi-static triaxial compression tests to evaluate dilational stress states at confining pressures of 725, 1450, 2175, and 2900 psi; and (5) confined triaxial creep experiments to evaluate the time-dependent behavior of the salt at axial stress differences of 4000 psi, 3500 psi, 3000 psi, 2175 psi and 2000 psi at 55 C and 4000 psi at 35 C, all at a constant confining pressure of 4000 psi. All comments, inferences, discussions of the Richton characterization and analysis are caveated by the small number of tests. Additional core and testing from a deeper well located at the proposed site is planned. The Richton rock salt is generally inhomogeneous as expressed by the density and velocity measurements with depth. In fact, we treated the salt as two populations, one clean and relatively pure (> 98% halite), the other salt with abundant (at times) anhydrite. The density has been related to the insoluble content. The limited mechanical testing completed has allowed us to conclude that the dilatational criteria are distinct for the halite-rich and other salts, and that the dilation criteria are pressure dependent. The indirect tensile strengths and unconfined compressive strengths determined are consistently lower than other coastal domal salts. The steady-state-only creep model being developed suggests that Richton salt is intermediate in creep resistance when compared to other domal and bedded salts. The results of the study provide only limited information for structural modeling needed to evaluate the integrity and safety of the proposed cavern field. This study should be augmented with more extensive testing. This report documents a series of test methods, philosophies, and empirical relationships, etc., that are used to define and extend our understanding of the mechanical behavior of the Richton salt. This understanding could be used in conjunction with planned further studies or on its own for initial assessments.
This report investigates the validity of several key assumptions in classical plasticity theory regarding material response to changes in the loading direction. Three metals, two rock types, and one ceramic were subjected to non-standard loading directions, and the resulting strain response increments were displayed in Gudehus diagrams to illustrate the approximation error of classical plasticity theories. A rigorous mathematical framework for fitting classical theories to the data, thus quantifying the error, is provided. Further data analysis techniques are presented that allow testing for the effect of changes in loading direction without having to use a new sample and for inferring the yield normal and flow directions without having to measure the yield surface. Though the data are inconclusive, there is indication that classical, incrementally linear, plasticity theory may be inadequate over a certain range of loading directions. This range of loading directions also coincides with loading directions that are known to produce a physically inadmissible instability for any nonassociative plasticity model.
American Rock Mechanics Association - 40th US Rock Mechanics Symposium, ALASKA ROCKS 2005: Rock Mechanics for Energy, Mineral and Infrastructure Development in the Northern Regions
Bauer, Stephen J.; Munson, D.E.; Hardy, M.P.; Barrix, J.; McGunegle, B.
Stress measurements have been obtained from within the Norton Mine in support of site characterization activities intended to determine the in situ stress field around the mine. These results together with other measurements in the area permit an estimate of the principal stresses at the mine. Based on the most recent measurements, the maximum (σHmax) and minimum (σHmin) stresses acting in the horizontal plane are oriented nearly east-west and north-south, respectively, and their magnitudes are 5330 psi and 4100 psi, respectively. These values are expected to be essentially uniform within a few hundred feet vertically above and below the mine elevation. The stress acting in the vertical direction has a magnitude of 3270 psi at the mine level. This measured vertical stress is related to the overburden weight according to σv=1.26ρgh (where ρ is the overburden density, g acceleration of gravity, and h overburden depth). The measured vertical stress exceeds the stress calculated from overburden weight by a factor of 1.26. These in situ stresses are assumed to be principal stresses and, as a result, the vertical stress is the minimum principal stress. These measurements are generally consistent in magnitude and direction with two other much older sets of measurements taken in the mine and they are consistent with the east-west trend of the regional in situ principal stress direction. The average of all three sets of measurements, recent and old, in the mine give a maximum horizontal stress of 6110 psi, a minimum horizontal stress of 3630, and a vertical stress of 3030 psi. The directions of the mine excavation development, which normally are oriented according to the principal stresses, are also consistent with the current and past measurements.
We have concluded a laboratory study to evaluate the survival potential of polymeric materials used for lost circulation plugs in geothermal wells. We learned early in the study that these materials were susceptible to hydrolysis. Through a systematic program in which many potential chemical combinations were evaluated, polymers were developed which tolerated hydrolysis for eight weeks at 500 F. The polymers also met material, handling, cost, and emplacement criteria. This screening process identified the most promising materials. A benefit of this work is that the components of the polymers developed can be mixed at the surface and pumped downhole through a single hose. Further strength testing is required to determine precisely the maximum temperature at which extrusion through fractures or voids causes failure of the lost circulation plug.
This document is the final report for the Compressed Air Energy Storage Monitoring to Support Refrigerated-Mined Rock Cavern Technology (CAES Monitoring to Support RMRCT) (DE-FC26-01NT40868) project to have been conducted by CAES Development Co., along with Sandia National Laboratories. This document provides a final report covering tasks 1.0 and subtasks 2.1, 2.2, and 2.5 of task 2.0 of the Statement of Project Objectives and constitutes the final project deliverable. The proposed work was to have provided physical measurements and analyses of large-scale rock mass response to pressure cycling. The goal was to develop proof-of-concept data for a previously developed and DOE sponsored technology (RMRCT or Refrigerated-Mined Rock Cavern Technology). In the RMRCT concept, a room and pillar mine developed in rock serves as a pressure vessel. That vessel will need to contain pressure of about 1370 psi (and cycle down to 300 psi). The measurements gathered in this study would have provided a means to determine directly rock mass response during cyclic loading on the same scale, under similar pressure conditions. The CAES project has been delayed due to national economic unrest in the energy sector.
This report summarizes recent reviews, observations, and analyses believed to be imperative to our understanding of the recent two million cubic feet salt fall event in Big Hill Cavern 103, one of the caverns of the Strategic Petroleum Reserve (SPR). The fall was the result of one or more stress driven mechanical instabilities, the origins of which are discussed in the report. The work has lead to important conclusions concerning the engineering and operations of the caverns at Big Hill. Specifically, Big Hill, being the youngest SPR site, was subjected to state-of-the-art solutioning methods to develop nominally well-formed, right-circular cylindrical caverns. Examination of the pressure history records indicate that operationally all Big Hill SPR caverns have been treated similarly. Significantly, new three-dimensional (3-D) imaging methods, applied to old (original) and more recent sonar survey data, have provided much more detailed views of cavern walls, roofs, and floors. This has made possible documentation of the presence of localized deviations from ''smooth'' cylindrical cavern walls. These deviations are now recognized as isolated, linear and/or planar features in the original sonar data (circa early 1990s), which persist to the present time. These elements represent either sites of preferential leaching, localized spalling, or a combination of the two. Understanding the precise origin of these phenomena remains a challenge, especially considering, in a historical sense, the domal salt at Big Hill was believed to be well-characterized. However, significant inhomogeneities in the domal salt that may imply abnormalities in leaching were not noted. Indeed, any inhomogeneities were judged inconsequential to the solution-engineering methods at the time, and, by the same token, to the approaches to modeling the rock mass geomechanical response. The rock mass was treated as isotropic and homogeneous, which in retrospect, appears to have been an over simplification. This analysis shows there are possible new opportunities regarding completing an appropriate site characterization for existing operating cavern fields in the SPR, as well as expansion of current sites or development of new sites. Such characterization should first be consistent with needs identified by this report. Secondly, the characterization needs to satisfy the input requirements of the 3-D solutioning calculational methods being developed, together with 3-D geomechanical analyses techniques which address deformation of a salt rock mass that contains inhomogeneities. It seems apparent that focusing on these important areas could preclude occurrence of unexpected events that would adversely impact the operations of SPR.
Since 1983, ground surface elevation data from the US DOE West Hackberry Strategic Petroleum crude oil storage facility has been routinely collected. The data have been assimilated, analyzed, and presented in terms of absolute elevations, subsidence rate, and estimates of volumetric changes of the storage facility. The information presented impacts operations and maintenance of the facility, and provides important constraints on the interpretation of ongoing structural analyses of the facility.
The elevation change data measured at the Bryan Mound Strategic Petroleum Reserve (SPR) site over the last 16+ years has been studied and a model utilized to project elevation changes into the future. The subsidence rate at Bryan Mound is low in comparison with other Strategic Petroleum Reserve sites and has decreased with time due to the maintenance of higher operating pressures and the normal decrease in creep closure rate of caverns with time. However, the subsidence at the site is projected to continue. A model was developed to project subsidence values 20 years into the future; no subsidence related issues are apparent from these projections.
The elevation change data measured at the Big Hill SPR site over the last 10 years has been studied and a model utilized to project elevation changes into the future. The subsidence rate at Big Hill is low in comparison with other Strategic Petroleum Reserve sites and has decreased with time due to the maintenance of higher operating pressures and the normal decrease in creep closure rate of caverns with time. However, the subsidence at the site is projected to continue. A model was developed to project subsidence values 20 years into the future; no subsidence related issues are apparent from these projections.
The elevation change data measured at the Weeks Island SPR site over the last 16+ years has been studied and analyzed. The subsidence rate is not constant with time and while the subsidence rate may have increased slightly during the past several years, recently the rate has increased more dramatically. The most recent increase comes at a time when the Strategic Petroleum Reserve (SPR) storage mine had been emptied of oil and was in the process of being refilled with brine. Damage to surface structures that has been observed during the past 12-18 months is attributed to the continued subsidence and dtierential subsidence across structures. The recent greater subsidence rates were unanticipated according to analysis results and will be used to aid further subsidence model development.
The elevation change data measured at the West Hackberry SPR site over the last 14+ years has been studied and a model utilized to project elevation changes into the future. The subsidence rate has decreased with time due to instituting maintenance of higher operating pressures for caverns (since about 1990) and the normal decrease in creep closure rate of caverns with time. However, the subsidence at the site is projected to continue. As a result, low lying regions exist and the extents of these regions are projected to increase with time. These low lying regions are susceptible to inundation with water from Black Lake and/or hurricane storm surges. This work may assist DOE in planning the construction and location of mitigative measures for flood control.
The first sinkhole at the Weeks Island Strategic Petroleum Reserve (SPR) site was initially observed in May 1992. Concurrent with the increasing dissolution of salt over the mined oil storage area below, it has gradually enlarged and deepened. Beginning in 1994 and continuing to the present, the injection of saturated brine directly into the sinkhole throat some 76 m beneath the ground surface essentially arrested further dissolution, providing time to make adequate preparation for the safe and orderly transfer of crude oil to other storage facilities. This mitigation measure marked the first time that such a control procedure has been used in salt mining; previously all control has been achieved by either in-mine or from-surface grouting. A second and much smaller sinkhole was noticed in early 1995 on an opposite edge of the SPR mine, but with a very similar geological and mine mechanics setting. Both sinkholes occur where the edges of upper 152 m and lower 213 m mined storage levels are nearly vertically aligned. Such coincidence maximizes the tensional stress development, leading to fracturing in the salt. This cracking takes 20 or more years to develop. The cracks then become flow paths for brine incursion, which after time progress into the mined openings. Undersaturated ground water gradually enlarges the cracks in salt through dissolution, leading to eventual collapse of the overlying sand to form sinkholes. Other geologic conditions may also be secondary factors in controlling both mining extent and sinkhole location.
This report is a critical reassessment of the geotechnical risks of continuing oil storage at the Weeks Island Strategic Petroleum Reserve site. It reviews all previous risk abatement recommendations, subsequent mitigative actions, and new information. Of increased concern, due to the discovery of a surface levels, is the long term maintainability of the mine as an oil storage repository. Mine operational changes are supported in order to facilitate monitoring of water entry diagnostics. These changes are also intended to minimize the volume in the mine available for water entry. Specific recommendations are made to implement the mine changes.
In early October of 1993, an oil shipment of about 1 million barrels was made from the Bayou Choctaw Strategic Petroleum Reserve storage facility to St. James Terminal. During the shipment, oil temperatures and soil temperatures along the pipeline were recorded. The field data were used to make estimations of soil thermal properties, thermal conductivity and specific heat. These data were also used to validate and calibrate a heat transfer code, OILPIP, which has been used to calculate pipeline cooling of oil during a drawdown.
Rock mass mechanical properties are important in the design of drifts and ramps. These properties are used in evaluations of the impacts of thermomechanical loading of potential host rock within the Yucca Mountain Site Characterization Project. Representative intact rock and joint mechanical properties were selected for welded and nonwelded tuffs from the currently available data sources. Rock mass qualities were then estimated using both the Norwegian Geotechnical Institute (Q) and Geomechanics Rating (RMR) systems. Rock mass mechanical properties were developed based on estimates of rock mass quality, the current knowledge of intact properties, and fracture/joint characteristics. Empirical relationships developed to correlate the rock mass quality indices and the rock mass mechanical properties were then used to estimate the range of rock mass mechanical properties.