ABSTRACT:

Abandoned Cavern 4 on the Bayou Choctaw Dome sits within the U.S. Strategic Petroleum Reserve property and requires monitoring and periodic assessments of stability. The cavern was originally drilled for brine production in 1935 and was abandoned in 1954 following the collapse of the nearby Cavern 7. The abandoned cavern presents several present-day problems that the U.S. Department of Energy must contend with: (i) its roof currently extends into caprock (ii) it has never held pressure at the wellhead, (iii) it is centrally located at the Bayou Choctaw dome adjacent to surface infrastructure, (iv) it exhibits a number of similarities to Cavern 7 prior to its collapse in 1954 to form current-day Cavern Lake, and (v) state regulations require a monitoring plan (even though it is abandoned). This paper evaluates the structural stability in Cavern 4 through the geomechanical analyses using a numerical model capturing realistic geometries. The results from the analysis indicate that any sort of caprock roof collapse for Cavern 4 is not imminent; however, the uncertainty due to salt falls illustrates the importance of continued monitoring of the area around BC-4 for behavior such as subsidence and tilt which may indicate a change in the cavern's integrity status.

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