Abstract:
This report presents computational analyses that simulate the structural response of crude oil storage caverns at the U.S. Strategic Petroleum Reserve (SPR) West Hackberry site in Louisiana. These analyses evaluate the geomechanical behavior of the 22 caverns at the West Hackberry SPR site for the current condition of the caverns and their wellbores, the effect of the caverns on surface facilities, and for potential enlargement related to drawdowns. These analyses represent a significant upgrade in modeling capability, as the following enhancements have been developed: a 6-million-element finite element model of the entire West Hackberry dome; cavern finite element mesh geometries fit to sonar measurements of those caverns; the full implementation of the multi-mechanism deformation (M-D) creep model; and the use of historic wellhead pressures to analyze the past geomechanical behavior of the caverns. The analyses examined the overall performance of the West Hackberry site by evaluating surface subsidence, horizontal surface strains, and axial well strains. This report presents a case study of how large-scale computational analyses may be used in conjunction with site data to make recommendations for safe depressurization and repressurization of oil storage caverns with unusual geometries and close proximity, and for the determination of the number of available drawdowns for a particular cavern.
Introduction
The U.S. Strategic Petroleum Reserve (SPR), operated by the U.S. Department of Energy (DOE), stores crude oil in solution-mined caverns in the salt dome formations of the Gulf Coast. Until recently, there were a total of 62 caverns located at four different sites in Texas (Bryan Mound and Big Hill) and Louisiana (Bayou Choctaw and West Hackberry); within the past year, the SPR has decided to decommission West Hackberry Cavern 6 and Bryan Mound Cavern 2, reducing the number of SPR caverns to 60. Each cavern is constructed and then operated using casings inserted through a wellbore or wellbores that are lined with steel casings cemented in place from the surface to near the top of the cavern. The West Hackberry salt dome in the extreme southwestern corner of Louisiana, some 24 km from the Louisiana/ Texas border to the west and the Gulf of Mexico to the south. It has an oil storage capacity of about 35×106 m3 (222×106 barrels) within 21 caverns, and has operated since 1980.
