A Coupled Thermal-Hydro-Mechanical Model for Wellbore Stability Analysis of Heavy Oil Reservoir

Cyclic steam stimulation has become an important method of heavy oil reservoir. Rock deformation and failure near wellbore region involves more complicated physical fields including temperature, seepage and stress in the process of cyclic steam stimulation. High temperature steam is injected to formation that causes rock skeleton stress, formation pore pressure and temperature to change. It’s necessary to study the effects of the coupled seepage, stress and temperature fields on wellbore stability in heavy oil reservoirs. We develop a fully coupled thermo-hydro-mechanical model for simulating wellbore stability for thermal recovery wells based on seepage mechanics, rock mechanics and thermodynamics. As an example of application, the model has been applied to analyze the influences of different injection-production parameters on temperature field, pressure field and gravel layer offset near wellbore in thermal recovery wells in the Bohai oilfield of China. Formation pore pressure and temperature have drastically changed within specific distance near wellbore after multi-cyclic steam stimulation. However, improving the steam injection rate will slightly increase the temperature of the heating area, its influence on the heating zone radius is not obvious, but the pressure field changes significantly near wellbore. The possibility of sand production increases quickly when production pressure difference is more than 3 MPa, production pressure is suggested to be generally controlled in 2.5 MPa ~ 3 MPa; When the steam injection rate is 500 m³ / d, it lead to formation of plastic strain increase, and the gravel layer offset is more than a third of its thickness, which means increasing the failure possibility of sand control.