Title: 3D Geomechanical Analysis of Multiple Caverns in Bedded Salt
Abstract: ABSTRACT This paper summarizes results from a recently concluded research project sponsored by the Gas Research Institute, the Petroleum Research Technology Council, and the US Department of Energy. The primary objective of this work has been to improve the state-of-the-art for designing and operating single and multiple caverns in thin bedded salt formations. The effort has included a geologic and geomechanical review of the Permian, Michigan, and Appalachian basins, followed by geomechanical modeling for single and multiple caverns in layered media. A modified creep viscoplastic model has been developed and implemented in Flac3D to simulate bedded salt material behavior. Both cyclic pressure operations and direct pressure drawdown are simulated. Cavern design parameters are varied to evaluate how they influence propagation of damage and the deformation of cavern. These are the cavern pressure, operating conditions, cavern size expressed in terms of height/diameter (H/D) ratio, overburden stiffness and roof thickness. The baseline results for single cavern simulations illustrate a shear stress distribution primarily around the cavern top and bottom corners, salt damage mainly around the cavern sidewall and slippage in the top interface between the salt formation and the anhydrite layer. During cyclic pressure operations, the shear-stress zones propagate into a wider region, which is responsible for an increase in the amount of slippage in the interface. During cyclic pressure loading, the magnitude of the maximum shear stress does not increase, resulting in no additional damage (micro-cracks) in the surrounding salt. The influence of the overburden stiffness is shown to be a critical parameter on the overall cavern response. A substantial part of the weight of the overburden material is carried by the anhydrite layer and by the cavern roof itself. For this particular case, the anhydrite reaches it tensile limit and fails. This failure implies that the cavern roof is subjected to a much higher load and therefore the amount and extension of damage increases substantially. We further evaluate minimum safe center to center distance of multiple horizontal caverns. We find that a center to center distance of two cavern diameters is not sufficient to eliminate the mutual interaction. Increasing the center to center distance to three cavern diameters, however, generally eliminates most interaction.
Publication Year: 2005
Publication Date: 2005-01-01
Language: en
Type: article
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Cited By Count: 11
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