Upscaling techniques for fully coupled THM simulation and application to hydrate gas production tests

Numerical simulation is important for practical and efficient assessment of hydrate reservoir formation stability and gas production potential. The history-matching simulation of hydrate gas production tests is complex due to coupled THM (thermo-hydro-mechanical) phenomena. The well log data from the Eastern Nankai Trough methane gas production site suggest vertically heterogeneous field properties. In the previous numerical simulation research of this site, the heterogeneous geological data were homogenized by adopting the standard mean-field theory, which can potentially lead to inaccurate simulation results due to the mesh size effect. By introducing new upscaling techniques for the permeability profiles and mechanical responses, a revised homogenization approach is proposed to improve the coupled THM simulation accuracy. In this study, seven gas production simulations of a hypothetical reservoir, six simulations of the Eastern Nankai Trough gas production test, and four simulations of the randomly generated site formation production test with different mesh sizes and different homogenization approaches were carried out to demonstrate that the proposed upscaling techniques can improve the accuracy of the simulation results with a coarse mesh model. This work, in turn, provides researchers and field engineers a much quicker way to assess the complex geomechanical behaviors of hydrate gas production site.