Geomechanical simulations are often used to study the deformation and mechanical failure behaviour of caprock formations in a SAGD operation. Different assumptions are made when building the simulation models. Usually the overburden formations above the reservoir are described by a limited number of vertically separated layers with varying thickness. Each layer is assumed homogeneous with laterally uniform material properties. In many cases, these simplifications are not accurate. It is important that the simulations properly consider the vertical and lateral variations.

This paper presents a probabilistic analysis on caprock integrity using a randomized finite element simulation approach. Volume of shale (VSH) logs and X-ray Diffraction (XRD) analysis data are used to generate stochastic distribution of 3 major litho-facies: sands, shale with low illite/smectite (I/S) contents and shale with high I/S contents. The litho-facie distributions are then mapped onto the finite element discretization of simulation models. Mechanical properties of the 3 major litho-facies are measured in a geomechanical laboratory test program. The geomechanical finite element model is coupled with thermal reservoir simulation results to study the deformation behaviour of caprock during a SAGD operation. Following a number of simulations, the results are statistically analyzed to estimate the probability of the caprock to enter plastic yielding.

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