Optimization of gas injection and energy replenishment for depletion development of fractured carbonate condensate gas reservoirs

During the depletion-based development of fractured carbonate reservoirs for condensate gas production, the decline in reservoir pressure and the complex fluid phases are prone to induce reverse condensation, stress sensitivity, and well wall instability. Reasonable gas injection replenishment can effectively maintain the formation pressure. Therefore, experiments on the mechanics and properties of fractured carbonate reservoirs in a certain block of Xinjiang were carried out. Based on this, a component mechanism model of the reservoir numerical simulation for the target reservoir was constructed, and the research on the pressure variation laws was conducted. From the aspects of maintaining well wall stability and increasing production capacity, single-well gas injection production replenishment optimization research for condensate gas reservoirs was carried out. The results show that the reservoir in this block exhibits significant stress sensitivity characteristics. The increase in confining pressure results in a permeability reduction ranging from 73.26% to 79.46%, and causes a 5.35% to 16.62% loss in production capacity. During the depletion-based development process, the decline in production capacity is mainly caused by reverse condensation and the deterioration of permeability induced by stress sensitivity. The numerical simulation results show that gas injection replenishment development under typical working conditions can effectively increase the production of condensate oil and gas, with an increase of up to 2.80% and 15.66% respectively. The optimization results indicate that the best oil production effect is achieved when gas injection is carried out at a gas injection rate slightly above the dew point pressure and in multiple cycles (with each injection stage lasting 3 months) at a gas injection speed of 40×10⁴ m³/d. This research provides theoretical basis and technical support for the optimization of development schemes for similar fractured carbonate reservoirs for condensate gas production.