Multi-field coupling mechanism and optimization of heat transfer in deep carbonate geothermal reservoirs based on acid fracturing modification
Xinghui Wu, Li Peng, Shengjun Miao, Meifeng Cai, Yan Liu, Min Wang, Wensai Xiong
Abstract
Efficient development of deep carbonate thermal reservoirs is crucial for geothermal resource utilization, but their low permeability and long-term thermal decay problems seriously limit their capacity. Taking the D22 well in Xiongan New Area as an example, we constructed a multi-field coupled Thermo-Hydro-Mechanical-Chemical (THMC) numerical model. We revealed the heat exchange mechanism and heat attenuation law of the reservoir after acid fracturing and reforming. The study shows that increasing the acid fracture opening from 0.08 m to 0.12 m increases permeability by 35% and heat exchange efficiency by 20%, but the increase in opening accelerates the cold front advance and leads to fracture closure. The main control parameters of fracture opening, well distance, and injection flow rate were identified, and the "stepped dynamic flow rate control method" was proposed to adjust the flow rate in steps (200→160→120 m 3 /h), which reduced the temperature decay rate by 42% and increased the cumulative heat extraction by 18%. Further design of a 10-12 mm nano-aerogel wellbore thermal barrier coating reduces heat loss by 15% and extends system life by 2-3 years after synergistic optimization. For large-scale reservoir development, "medium reservoir size (3-4 km 2 ) periodic acid recharge" is proposed to suppress the diminishing marginal benefits.