Thermal-Hydraulic Numerical Simulation for Horizontal Wells in Naturally Fractured Carbonate Oil Reservoirs Considering Thermal-Induced Fracture Permeability Variations

For the economic development of naturally fractured carbonate oil reservoirs, horizontal well waterflooding is extensively utilized. Through long-term injection of cold water, the temperature differences during the cooling process of the reservoir rocks lead to the emergence of thermal effect, which induces changes in fracture permeability and consequently alters the overall waterflooding performance. However, there is a scarcity of numerical simulation studies that explore how this thermal effect influences the production performance of the whole system. To bridge this gap, a fracture permeability variation model considering the thermal effect is developed based on the concept of a dual porosity and dual permeability (DPDK) model, and a corresponding thermal-hydraulic simulation method for naturally fractured carbonate oil reservoir is established. Then different simulation cases are designed to investigate the influence of the thermal effect on the waterflooding performance in a horizontal wells group. The related simulation results reveal that after considering the impact of thermal effects on the permeability of natural fractures, the permeability of natural fractures increases within the low temperature swept front range, causing the overall waterflooding front speed within the natural fracture system to accelerate, while the waterflooding front speed within the matrix system is slower. This leads to a rapid response and high oil production rate in the early stages of the oil production well. However, due to the fast advancement of the waterflooding front in the natural fracture system, it also results in an earlier water breakthrough in oil wells, leading to a lower oil production rate and a higher water production rate in the mid-to-late stages, which is not conducive to long-term production. The results and insights obtained in this paper, can provide significant theoretical support for accurately understanding the water breakthrough patterns in a horizontal well during the waterflooding development phase of carbonate oil reservoirs and formulating relevant production schedules.