Upscaling of Mechanical Properties in Heterogeneous Reservoirs for Compaction Analysis

Geo-mechanical grid of reservoir simulations often contains coarse cells (×1 m thick) compared with the sub-metre resolutions of well log data. The geomechanical properties of the coarse cells are usually assumed to be representative of well log data although a rigorous upscaling process is lacking. A few existing studies on the upscaling methods have mainly focused on elastic properties. Guidelines for the upscaling of other mechanical properties related to plasticity are still required.

This study aims to assess the upscaled material parameter including elastic and visco-plastic material in heterogeneous chalk reservoirs for compaction analysis which are optimized from history matching the surface subsidence. To this purpose, a 2D simulation case with over-burden, reservoir and under-burden is considered as a conceptual model. A random distribution of porosity field defines different mechanical properties within the reservoir based on porosity dependent functions which are collected for chalk. Our results demonstrate the shape of yield surface is the most important parameter for upscaling while other upscaled material parameters are relatively close to the values obtained from the material with mean porosity. These imply that the heterogeneity has the most effect on the shape of the yield surface.