Publications
Analysis of Cavern and Well Stability at the Bryan Mound SPR Site Using the M D Salt Creep Model
This report presents computational analyses that simulate the structural response of caverns at the Strategic Petroleum Reserve Bryan Mound site. The cavern field comprises 20 caverns. Five caverns (1, 2, 4, and 5; 3 was later plugged and abandoned) were acquired from industry and have unusual shapes and a history dating back to 1946. The other 16 caverns (101-116) were leached according to SPR standards in the mid-1980s and have tall cylindrical shapes. The history of the caverns and their shapes are simulated in a 3-D geomechanics model of the site that predicts deformations, strains, and stresses. Historical wellhead pressures are used to calculate cavern pressures up through July 2016. Because of the extent of heterogeneous creep behavior observed throughout the Bryan Mound site, a set of cavern-specific creep coefficients was developed to produce better matches with measured cavern closure and surface subsidence. For this new implementation of the model, there are two significant advances: the use of the multimechanism deformation (M-D) salt creep model to evaluate both steady-state and transient salt creep; and the creation of finite element mesh geometries for the caverns that nearly exactly match the geometries obtained through sonar measurements. The results of the finite element model are interpreted to provide information on the current and future status of subsidence, well integrity, cavern stability, and drawdown availability. The analyses shown in this report demonstrate that the use of sonar-based cavern geometries provide a more detailed evaluation of the effects of cavern pressure changes on stress behavior in the salt surrounding the cavern, and thus to evaluate long-term cavern integrity and evolution of drawdown availability. Some of the Bryan Mound caverns were shown to have less than five available drawdowns. Additionally, the choice of an alternate pressurization scenario for abandoned Cavern 3 gives further credence to the hypothesis that fluid is being forced up and out of the cavern into the caprock due to creep-induced closure. Finally, the model has been built with several options to allow for exploration of different parameter and operations scenarios; these will be particularly useful if a recent advance in the calculation speed using the M-D model is fully realized. ACKNOWLEDGEMENTS The authors would like to thank Anna Snider Lord, Byoung Yoon Park, Barry Roberts, Kirsten Chojnicki, and Dylan Moriarty, for their contributions to the work described in this report, and the U.S. Department of Energy, Strategic Petroleum Reserve office for their review and support of this work.