ABSTRACT
Mechanical analyses of the West Hackberry site were recently published (Sobolik & Ehgartner 2009), and they indicate that the dish-like shape of Cavern 6 make it prone to significant subsidence during normal operations, and may potentially be at risk of dilatant and tensile damage around the cavern perimeter during repressurization after a workover. The analyses in Sobolik & Ehgartner (2009) modeled the salt’s creep behavior with the power law creep model along with a reduced elastic
1 INTRODUCTION
The US Strategic Petroleum Reserve (SPR), operated by the U.S Department of Energy (DOE), stores crude oil in 62 caverns located at four different sites in Texas (Bryan Mound and Big Hill) and Louisiana (Bayou Choctaw and West Hackberry). The petroleum is stored in solution-mined caverns in salt dome formations. West Hackberry is located 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 (Munson, 2006). The geological characteristics related to the West Hackberry site were first described by Whiting (1980). The updated three-dimensional models of Rautman et al. (2004) used a more refined analysis of the data and produced models of the dome that differed slightly from the earlier models. The West Hackberry dome consists of the more-or-less typical geologic sequence of rocks. With increasing depth below the ground surface, initially there is roughly 480 m of soil and unconsolidated gravel, sand, and mud, followed by approximately 120 m of caprock, consisting of anhydrite and carbonate (a conversion product of anhydrite). Generally, the upper portions of the caprock consist of the anhydrite conversion products of gypsum and dolomite, while the lower portion of the caprock is the initial anhydrite residue from the solution of the original domal material. The caprock is generally lens shaped with the thickest part of the lens over the central portion of the dome, tapering to thin edges toward the periphery of the dome.
