Publications

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This report documents the progression of crude oil phase behavior modeling within the U.S. Strategic Petroleum Reserve vapor pressure program during the period 2004-2009. Improvements in quality control on phase behavior measurements in 2006 coupled with a growing body of degasification plant operations data have created a solid measurement baseline that has served to inform and significantly improve project understanding on phase behavior of SPR oils. Systematic tuning of the model based on proven practices from the technical literature have shown to reduce model bias and match observed data very well, though this model tuning effort is currently in process at SPR and based on preliminary data. The current report addresses many of the steps that have helped to build a strong baseline of data coupled with sufficient understanding of model features so that calibration is possible.

This report comprises an annual summary of activities under the U.S. Strategic Petroleum Reserve (SPR) Vapor Pressure Committee in FY2009. The committee provides guidance to senior project management on the issues of crude oil vapor pressure monitoring nd mitigation. The principal objectives of the vapor pressure program are, in the event of an SPR drawdown, to minimize the impact on the environment and assure worker safety and public health from crude oil vapor emissions. The annual report reviews key program areas ncluding monitoring program status, mitigation program status, new developments in measurements and modeling, and path forward including specific recommendations on cavern sampling for the next year. The contents of this report were first presented to SPR senior anagement in December 2009, in a deliverable from the vapor pressure committee. The current SAND report is an adaptation for the Sandia technical audience.

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Crude oil stored at the US Strategic Petroleum Reserve (SPR) requires mitigation procedures to maintain oil vapor pressure within program delivery standards. Crude oil degasification is one effective method for lowering crude oil vapor pressure, and was implemented at the Big Hill SPR site from 2004-2006. Performance monitoring during and after degasification revealed a range of outcomes for caverns that had similar inventory and geometry. This report analyzed data from SPR degasification and developed a simple degas mixing (SDM) model to assist in the analysis. Cavern-scale oil mixing during degassing and existing oil heterogeneity in the caverns were identified as likely causes for the range of behaviors seen. Apparent cavern mixing patterns ranged from near complete mixing to near plug flow, with more mixing leading to less efficient degassing due to degassed oil re-entering the plant before 100% of the cavern oil volume was processed. The report suggests that the new cavern bubble point and vapor pressure regain rate after degassing be based on direct in-cavern measurements after degassing as opposed to using the plant outlet stream properties as a starting point, which understates starting bubble point and overstates vapor pressure regain. Several means to estimate the cavern bubble point after degas in the absence of direct measurement are presented and discussed.

This report presents a model to estimate the spallings releases for the Waste Isolation Pilot Plant Performance Assessment (WIPP PA). A spallings release in the context of WIPP PA refers to a portion of the solid waste transported from the subsurface repository to the ground surface due to inadvertent oil or gas drilling into the WIPP repository at some time after site closure. Some solid waste will be removed by the action of the drillbit and drilling fluid; this waste is referred to as cuttings and cavings. If the repository is pressurized above hydrostatic at the time of intrusion, solid waste material local to the borehole may be subject to mechanical failure and entrainment in high-velocity gases as the repository pressure is released to the borehole. Solid material that fails and is transported into the wellbore and thus to the surface comprise the spallings releases. The spallings mechanism is analogous to a well blowout in the modern oil and gas drilling industry. The current spallings conceptual model and associated computer code, DRSPALL, were developed for the 2004 recertification because the prior spallings model used in the 1996 WIPP Compliance Certification Application (CCA) was judged by an independent peer review panel as inadequate (DOE 1996, 9.3.1). The current conceptual model for spallings addresses processes that take place several minutes before and after a borehole intrusion of a WIPP waste room. The model couples a pipe-flow wellbore model with a porous flow repository model, allowing high-pressure gas to flow from the repository to the wellbore through a growing cavity region at the well bottom. An elastic stress model is applied to the porous solid domain that allows for mechanical failure of repository solids if local tensile stress exceeds the tensile strength of the waste. Tensile-failed solids may be entrained into the wellbore flow stream by a fluidized bed model, in which case they are ultimately transported to the land surface comprising a release. In July 2003, DOE/SNL presented the spallings conceptual model to a independent peer review panel in accordance with NUREG 1297 guidelines (NRC, 1988). The panel ultimately judged the model as adequate for implementation in WIPP PA (Yew et al., 2003). This report documents the spallings model history from 1997 to the implementation of DRSPALL in the 2004 Compliance Recertification Application (CRA) (DOE, 2004). The scope of this report includes descriptions of the conceptual model, numerical model, verification and validation techniques, model sensitivity studies, and WIPP PA spallings results as presented in the 2004 CRA.

Crude oil storage caverns at the U.S. Strategic Petroleum Reserve (SPR) are solution-mined from subsurface salt domes along the U.S. Gulf Coast. While these salt domes exhibit many attractive characteristics for large-volume, long-term storage of oil such as low cost for construction, low permeability for effective fluids containment, and secure location deep underground, they also present unique technical challenges for maintaining oil quality within delivery standards. The vapor pressures of the crude oils stored at SPR tend to increase with storage time due to the combined effects of geothermal heating and gas intrusion from the surrounding salt. This presents a problem for oil delivery offsite because high vapor-pressure oil may lead to excessive atmospheric emissions of hydrocarbon gases that present explosion hazards, health hazards, and handling problems at atmospheric pressure. Recognizing this potential hazard, the U.S. Department of Energy, owner and operator of the SPR, implemented a crude oil vapor pressure monitoring program that collects vapor pressure data for all the storage caverns. From these data, DOE evaluates the rate of change in vapor pressures of its oils in the SPR. Moreover, DOE implemented a vapor pressure mitigation program in which the oils are degassed periodically and will be cooled immediately prior to delivery in order to reduce the vapor pressure to safe handling levels. The work described in this report evaluates the entire database since its origin in 1993, and determines the current levels of vapor pressure around the SPR, as well as the rate of change for purposes of optimizing both the mitigation program and meeting safe delivery standards. Generally, the rate of vapor pressure increase appears to be lower in this analysis than reported in the past and, problematic gas intrusion seems to be limited to just a few caverns. This being said, much of the current SPR inventory exceeds vapor pressure delivery guidelines and must be degassed and cooled in order to meet current delivery standards.

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Oil caverns at the U.S. Strategic Petroleum Reserve (SPR) are subjected to geothermal heating from the surrounding domal salt. This process raises the temperature of the crude oil from around 75 F upon delivery to SPR to as high as 130 F after decades of storage. While this temperature regime is adequate for long-term storage, it poses challenges for offsite delivery, with warm oil evolving gases that pose handling and safety problems. SPR installed high-capacity oil coolers in the mid-1990's to mitigate the emissions problem by lowering the oil delivery temperature. These heat exchanger units use incoming raw water as the cooling fluid, and operate only during a drawdown event where incoming water displaces the outgoing oil. The design criteria for the heat exchangers are to deliver oil at 100 F or less under all drawdown conditions. Increasing crude oil vapor pressures due in part to methane intrusion in the caverns is threatening to produce sufficient emissions at or near 100 F to cause the cooled oil to violate delivery requirements. This impending problem has initiated discussion and analysis of alternative cooling methods to bring the oil temperature even lower than the original design basis of 100 F. For the study described in this report, two alternative cooling methods were explored: (1) cooling during a limited drawdown, and (2) cooling during a degas operation. Both methods employ the heat exchangers currently in place, and do not require extra equipment. An analysis was run using two heat transfer models, HEATEX, and CaveMan, both developed at Sandia National Laboratories. For cooling during a limited drawdown, the cooling water flowrate through the coolers was varied from 1:1 water:oil to about 3:1, with an increased cooling capacity of about 3-7 F for the test cavern Bryan Mound 108 depending upon seasonal temperature effects. For cooling in conjunction with a degas operation in the winter, cavern oil temperatures for the test cavern Big Hill 102 were cooled sufficiently that the cavern required about 9 years to return to the temperature prior to degas. Upon reviewing these results, the authors recommended to the U.S. Department of Energy that a broader study of the cooling during degas be pursued in order to examine the potential benefits of cooling on all caverns in the current degasification schedule.

A new conceptual model has been developed for drilling intrusion into the Waste Isolation Pilot Plant. The model is implemented in a new code, DRSPALL, which captures the physics of the spallings release phenomena. The new conceptual model and code required parallel development of a family of parameters that adequately describe the properties of the system. This report introduces the various parameters implemented in the new spallings model, and provides justification for values and ranges of new parameters not currently in the performance assessment database.

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