Publications

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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).

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Mixing of injected raw (undersaturated) water with brine in Strategic Petroleum Reserve (SPR) salt caverns affects the shape of cavern walls due to leaching. Cavern shape impacts cavern geomechanical stability and available volume for oil storage. Raw water injection occurs during initial solution mining of caverns, remedial leaching of caverns, and oil drawdown. Of interest are factors that control the degree of raw water-brine mixing and thereby the concentration of the aqueous fluid mixture that contacts the salt cavern walls. It is hypothesized that poorly-mixed fresh water could potentially cause undesirable and non-uniform leaching , for example, if buoyant poorly-mixed fresh water collects and preferentially leaches under the oil-brine interface . This report presents current understanding of controls on incomplete-to-complete mixing of raw water and brine, focusing on implications for SPR cavern leaching. In the context of mixing, we review the following: SPR leaching operations; models of leaching; field measurements of leaching and cavern shapes; and previous laboratory experiments of mixing and /or leaching performed at Sandia National Laboratories. We present recent laboratory experiments in 2014-2016 that focused explicitly on understanding controls of poor-to-well mixed conditions. We find that well-mixed conditions are expected for typical operating conditions of the SPR.

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This memo documents the mechanical loading analysis performed on the second set of DTOcean program WP4 foundation and anchor systems submodule design iterations [4]. Finite Element Analysis (FEA) simulations were performed to validate design requirements defined by Python based analytic simulations of the WP4 program Naval Facilities Engineering Command (NAVFAC) tool. This FEA procedure focuses on worst case loading scenarios on shallow gravity foundation and pile anchor designs produced by WP4. These models include a steel casing and steel anchor with soft clay surrounding the steel components respectively.

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This memo documents the mechanical loading analysis performed to date for the DTOcean program WP4 foundation and anchor systems submodule. FEA simulations were performed to validate design requirements defined by Python based analytic simulations of the WP4 program Naval Facilities Engineering Command (NAVFAC) tool. This FEA procedure focuses on worst case loading scenarios on direct mbedment anchor and suction caisson designs produced by WP4. These models include a steel casing and steel anchor with soft clay and dense sand surrounding the steel components respectively.

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.

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The nature of geologic disposal of nuclear waste in salt formations requires validated and verified two-phase flow models of transport of brine and gas through intact, damaged, and consolidating crushed salt. Such models exist in other realms of subsurface engineering for other lithologic classes (oil and gas, carbon sequestration etc. for clastics and carbonates) but have never been experimentally validated and parameterized for salt repository scenarios or performance assessment. Models for waste release scenarios in salt back-fill require phenomenological expressions for capillary pressure and relative permeability that are expected to change with degree of consolidation, and require experimental measurement to parameterize and validate. This report describes a preliminary assessment of the influence of consolidation (i.e. volume strain or porosity) on capillary entry pressure in two phase systems using mercury injection capillary pressure (MICP). This is to both determine the potential usefulness of the mercury intrusion porosimetry method, but also to enable a better experimental design for these tests. Salt consolidation experiments are performed using novel titanium oedometers, or uniaxial compression cells often used in soil mechanics, using sieved run-of-mine salt from the Waste Isolation Pilot Plant (WIPP) as starting material. Twelve tests are performed with various starting amounts of brine pore saturation, with axial stresses up to 6.2 MPa (~900 psi) and temperatures to 90°C. This corresponds to UFD Work Package 15SN08180211 milestone “FY:15 Transport Properties of Run-of-Mine Salt Backfill – Unconsolidated to Consolidated”. Samples exposed to uniaxial compression undergo time-dependent consolidation, or creep, to various degrees. Creep volume strain-time relations obey simple log-time behavior through the range of porosities (~50 to 2% as measured); creep strain rate increases with temperature and applied stress as expected. Mercury porosimetry is used to determine characteristic capillary pressure curves from a series of consolidation tests and show characteristic saturation-capillary pressure curves that follow the common van Genuchten (1978, 1980) formulation at low stresses. Higher capillary pressure data are suspect due to the large potential for sample damage, including fluid inclusion decrepitation and pore collapse. Data are supportive of use of the Leverett “J” function (Leverett, 1941) to use for scaling characteristic curves at different degrees of consolidation, but better permeability determinations are needed to support this hypothesis. Recommendations for further and refined testing are made with the goal of developing a self- consistent set of constitutive laws for granular salt consolidation and multiphase (brine-air) flow.

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, introduced herein, is a demonstration of the DBD concept and these advances.

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.

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The nature of geologic disposal of nuclear waste in salt formations requires validated and verified two - phase flow models of transport of brine and gas through intact, damaged, and consolidating crushed salt. Such models exist in oth er realms of subsurface engineering for other lithologic classes (oil and gas, carbon sequestration etc. for clastics and carbonates) but have never been experimentally validated and parameterized for salt repository scenarios or performance assessment. Mo dels for waste release scenarios in salt back - fill require phenomenological expressions for capillary pressure and relative permeability that are expected to change with degree of consolidation, and require experimental measurement to parameterize and vali date. This report describes a preliminary assessment of the influence of consolidation (i.e. volume strain or porosity) on capillary entry pressure in two phase systems using mercury injection capillary pressure (MICP). This is to both determine the potent ial usefulness of the mercury intrusion porosimetry method, but also to enable a better experimental design for these tests. Salt consolidation experiments are performed using novel titanium oedometers, or uniaxial compression cells often used in soil mech anics, using sieved run - of - mine salt from the Waste Isolation Pilot Plant (WIPP) as starting material. Twelve tests are performed with various starting amounts of brine pore saturation, with axial stresses up to 6.2 MPa (%7E900 psi) and temperatures to 90 o C. This corresponds to UFD Work Package 15SN08180211 milestone "FY:15 Transport Properties of Run - of - Mine Salt Backfill - Unconsolidated to Consolidated". Samples exposed to uniaxial compression undergo time - dependent consolidation, or creep, to various deg rees. Creep volume strain - time relations obey simple log - time behavior through the range of porosities (%7E50 to 2% as measured); creep strain rate increases with temperature and applied stress as expected. Mercury porosimetry is used to determine characteri stic capillary pressure curves from a series of consolidation tests and show characteristic saturation - capillary pressure curves that follow the common van Genuchten (1978, 1980) formulation at low stresses. Higher capillary pressure data are suspect due t o the large potential for sample damage, including fluid inclusion decrepitation and pore collapse. Data are supportive of use of the Leverett "J" function (Leverett, 1941) to use for scaling characteristic curves at different degrees of consolidation, but better permeability determinations are needed to support this hypothesis. Recommendations for further and refined testing are made with the goal of developing a self - consistent set of constitutive laws for granular salt consolidation and multiphase (brin e - air) flow.

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