Linear Finite Element Analyses of Stresses Redistribution and Ground Subsidence due to Cavern Excavation in Hard Rocks for Crude Oil Storage

Underground storage of crude oil and different types of gases such as natural gas, Carbon Dioxide and hydrogen as well as LPG and LNG has received a great attention during the past decades due to several advantages that it offers. In addition to the depleted oil/gas reservoirs that are commonly used for storage purposes, construction of caverns in hard rocks, leached salt cavities, aquifers, abandoned mines and coal seams has gained great attention. In this paper, the results of numerical geo-mechanical studies of constructing a tunnel-shaped cavern with a rectangular cross-section constructed in the hard rock for crude oil storage are presented. A finite element program was developed in this study assuming homogenous isotropic linear elastic properties for the material. So, at first a mesh generator program was developed for this especial structure analysis. This in-house finite element program was developed according to isoparametric formulation. Stress redistribution pattern due to the cavern construction was studied qualitatively and quantitatively. The equivalent von Mises stress quantity, describing the stresses status regarding yielding or failure was used in this work. The magnitudes of the equivalent von Mises stress were determined and compared before and after the cavern excavation at each Gaussian integral point inside the structure. This will determine the unstable rock zones especially considering the fact that linear analysis was employed in the current study. Then the nucleation of the shear zones was determined. Detection of the shear zones is important considering its impact on the well integrity, well/casing shear rupture and damage, as well as the reactivation of pre-existing faults. Finally, the ground subsidence was determined for the upper surface of the model due to the cavern excavation which affects the stability of the structures and buildings existing above the cavern at ground level.

کلیدواژه ها:

Underground Storage of Crude Oil ، Finite Element Analyses ، Cavern in Hard Rock ، Stresses Redistribution Pattern ، Ground Subsidence