Investigation on Well Integrity During Geothermal Production from High Temperature Oil Wells

摘要

Geothermal energy is extracted by injecting cold water into high-temperature geothermal reservoir. Water injection causes the variations of temperature, pore pressure and effective stress in the swept region. Subsequently, it also could induce wellbore deformation and compromise wellbore integrity. To address this issue, a thermo-hydro-mechanical (THM) coupled model is established to study the mechanical responses of reservoir and wellbore. The formation is simplified as a poroelastic medium with the degree of freedom of temperature. The THM responses of formation and the mechanical behavior of wellbores are simulated synchronously. Results indicate that the pore pressure decreases from injection well to production well, while the water temperature rises during flowing into production well. A low-temperature region (LTR) forms around the injection well and expands with time. The propagation speed of temperature is much slower than that of overpressure. The formation will uplift and move toward the production well, while in the last period, a reverse region near the injection well will subside. The geothermal recovery induces additional stress on casings, and especially stress concentration arises in the reservoir interval of injection well. This research provides a reference for evaluating formation response and wellbore integrity in geothermal development.