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Title: Proposed Methodology for Assessing Available Drawdowns for Each Oil Storage Cavern in the Strategic Petroleum Reserve.

Abstract

The Department of Energy maintains an up-to-date documentation of the number of available full drawdowns of each of the caverns owned by the Strategic Petroleum Reserve (SPR). This information is important for assessing the SPR's ability to deliver oil to domestic oil companies expeditiously if national or world events dictate a rapid sale and deployment of the oil reserves. What factors go into assessing available drawdowns? Determining the number of drawdowns requires the consideration of several factors regarding cavern and wellbore integrity and stability, including stress states caused by cavern geometry and operations, salt damage caused by dilatant and tensile stresses, the effect of enhanced creep on wellbore integrity, and the sympathetic stress effect of operations on neighboring caverns. A consensus has now been built regarding the assessment of drawdown capabilities and risks for the SPR caverns (Sobolik et al., 2014; Sobolik 2016). The process involves an initial assessment of the pillar-to-diameter (P/D) ratio for each cavern with respect to neighboring caverns. Ideally, it is desired to keep this value greater than 1.0, which is in line with most industry design standards and should ensure cavern integrity and prevent loss of fluids to the surrounding rock mass. However, many ofmore » the SPR caverns currently have a P/D less than 1.0, or will likely have a low P/D after one or two full drawdowns. For these caverns, it is important to examine the structural integrity with more detail using geomechanical models. Finite-element geomechanical models have been used to determine the stress states in the pillars following successive drawdowns. By computing the tensile and dilatant stresses in the salt, areas of potential structural instability can be identified that may represent "red flags" for additional drawdowns. These analyses have found that many caverns will maintain structural integrity even when grown via drawdowns to dimensions resulting in a P/D of less than 1.0. The analyses have also confirmed that certain caverns should only be completely drawn down one time. As the SPR caverns are utilized and partial drawdowns are performed to remove oil from the caverns (e.g., for occasional oil sales authorized by the Congress or the President), the changes to the cavern volumes casused by these procedures must be tracked and accounted for so that an ongoing assessment of the cavern's drawdown capacity may be continued. A proposed methodology for assessing and tracking the available drawdowns for each cavern is presented in this report. ACKNOWLEDGEMENTS This research is funded by SPR programs administered by the Office of Fossil Energy of the U.S. Department of Energy. The author would like to thank Diane Willard and Paul Malphurs of the U.S. Strategic Petroleum Reserve, and Anna Snider Lord of Sandia Labs for their review and support of this work.« less

Authors:
; ; ;
Publication Date:
Research Org.:
Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
Sponsoring Org.:
USDOE Office of Fossil Energy (FE), Petroleum Reserves (FE-40)
OSTI Identifier:
1528820
Report Number(s):
SAND2018-4518
663929
DOE Contract Number:  
AC04-94AL85000
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English

Citation Formats

Sobolik, Steven R., Hart, David, Park, Byoung, and Chojnicki, Kirsten. Proposed Methodology for Assessing Available Drawdowns for Each Oil Storage Cavern in the Strategic Petroleum Reserve.. United States: N. p., 2018. Web. doi:10.2172/1528820.
Sobolik, Steven R., Hart, David, Park, Byoung, & Chojnicki, Kirsten. Proposed Methodology for Assessing Available Drawdowns for Each Oil Storage Cavern in the Strategic Petroleum Reserve.. United States. doi:10.2172/1528820.
Sobolik, Steven R., Hart, David, Park, Byoung, and Chojnicki, Kirsten. Sun . "Proposed Methodology for Assessing Available Drawdowns for Each Oil Storage Cavern in the Strategic Petroleum Reserve.". United States. doi:10.2172/1528820. https://www.osti.gov/servlets/purl/1528820.
@article{osti_1528820,
title = {Proposed Methodology for Assessing Available Drawdowns for Each Oil Storage Cavern in the Strategic Petroleum Reserve.},
author = {Sobolik, Steven R. and Hart, David and Park, Byoung and Chojnicki, Kirsten},
abstractNote = {The Department of Energy maintains an up-to-date documentation of the number of available full drawdowns of each of the caverns owned by the Strategic Petroleum Reserve (SPR). This information is important for assessing the SPR's ability to deliver oil to domestic oil companies expeditiously if national or world events dictate a rapid sale and deployment of the oil reserves. What factors go into assessing available drawdowns? Determining the number of drawdowns requires the consideration of several factors regarding cavern and wellbore integrity and stability, including stress states caused by cavern geometry and operations, salt damage caused by dilatant and tensile stresses, the effect of enhanced creep on wellbore integrity, and the sympathetic stress effect of operations on neighboring caverns. A consensus has now been built regarding the assessment of drawdown capabilities and risks for the SPR caverns (Sobolik et al., 2014; Sobolik 2016). The process involves an initial assessment of the pillar-to-diameter (P/D) ratio for each cavern with respect to neighboring caverns. Ideally, it is desired to keep this value greater than 1.0, which is in line with most industry design standards and should ensure cavern integrity and prevent loss of fluids to the surrounding rock mass. However, many of the SPR caverns currently have a P/D less than 1.0, or will likely have a low P/D after one or two full drawdowns. For these caverns, it is important to examine the structural integrity with more detail using geomechanical models. Finite-element geomechanical models have been used to determine the stress states in the pillars following successive drawdowns. By computing the tensile and dilatant stresses in the salt, areas of potential structural instability can be identified that may represent "red flags" for additional drawdowns. These analyses have found that many caverns will maintain structural integrity even when grown via drawdowns to dimensions resulting in a P/D of less than 1.0. The analyses have also confirmed that certain caverns should only be completely drawn down one time. As the SPR caverns are utilized and partial drawdowns are performed to remove oil from the caverns (e.g., for occasional oil sales authorized by the Congress or the President), the changes to the cavern volumes casused by these procedures must be tracked and accounted for so that an ongoing assessment of the cavern's drawdown capacity may be continued. A proposed methodology for assessing and tracking the available drawdowns for each cavern is presented in this report. ACKNOWLEDGEMENTS This research is funded by SPR programs administered by the Office of Fossil Energy of the U.S. Department of Energy. The author would like to thank Diane Willard and Paul Malphurs of the U.S. Strategic Petroleum Reserve, and Anna Snider Lord of Sandia Labs for their review and support of this work.},
doi = {10.2172/1528820},
journal = {},
number = ,
volume = ,
place = {United States},
year = {2018},
month = {4}
}