ABSTRACT:

Cyclic steam stimulation has become an important method for enhancing the recovery of heavy oil reservoir. Accurate prediction of changes in pore pressure and stress within the near wellbore region during the stimulation is of critical importance for wellbore stability and sand production analyses. However, cyclic steam stimulation is a complicated process which involves complex interactions among multiphase fluid flow, heat transfer and elastoplastic deformation of the formation rock. In this present work, we developed a fully coupled thermo-hydro-mechanical model for simulating the cyclic steam stimulation of heavy oil reservoirs. A three-phase, two-component formulation is employed for characterizing the flow of oil and water/steam within the pore space. Elastoplastic deformation of the heavy oil reservoir rock is treated with the Mohr-Coulomb model. In addition to thermal conduction, thermal convection is also considered due to the high permeability frequently featured by heavy oil reservoirs. Mathematical equations governing these coupled physical processes are discretized and solved with the finite element method in a fully coupled manner. Validations of the model against analytical solutions to some simple problems have been performed, which demonstrate the capability of the model to capture the coupling behavior between pore fluid flow, heat transfer and deformation of the reservoir rock. As an example of application, the model has been applied to simulate the cyclic stream stimulation performed in horizontal wells drilled in a heavy oil reservoir in the Bohai oilfield of China. The sizes of the heated zones as well as the stress, temperature and pore pressure distributions around the wellbore under different injection parameters were predicted and some implications for wellbore stability have been presented.

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