Abstract: Tailwater reinjection is a necessary means to ensure the sustainable development of geothermal resource extraction. However, during tailwater reinjection, excessive injection pressure can damage the thermal reservoir, and tailwater quality may also impair the fluid flow capacity of the thermal reservoir. To ensure the safety and stability of thermal reservoir reinjection, taking the Guantao Formation thermal reservoir in the Xiong′an New Area as an example, a prediction model for the fracture pressure of the thermal reservoir was established to calculate and analyze the critical injection pressure for thermal reservoir reinjection; using numerical simulation methods, the effects of reinjection water temperature and injection pressure on reservoir porosity and permeability were studied; finally, a mathematical model for tailwater particle deposition was established to analyze the effects of suspended particle size, seepage velocity, and particle mass concentration on the permeability of the thermal reservoir. The study shows that under conditions below the fracture pressure of the thermal reservoir, the temperature and pressure of the reinjected tailwater do not have a significant impact on the porosity and permeability of the thermal reservoir. The changes in porosity and permeability are less than 2.00%, and thermal breakthrough will not occur within 100 years; tailwater quality can have a greater impact on the permeability of the thermal reservoir. During the tailwater reinjection process, attention must be paid to the impact of tailwater quality on the physical properties of the thermal reservoir. The research results can provide technical support for the safety and stability of tailwater reinjection operations in thermal reservoirs.

Key words: geothermal, tailwater reinjection, critical injection pressure, particle deposition, thermal reservoir