Evaluation methods and influence factors of heat extraction performance in hot dry rock reservoir under multi-field coupling

Abstract

How to improve the heat extraction performance of HDR (hot dry rock) is one of the most concerned problems in HDR extraction. The key is to take a reasonable method to evaluate the heat extraction performance of hot dry rock and find out the main factors influencing the heat extraction performance of hot dry rock. The permeability of HDR reservoir, well type, well spacing, well pattern and injection flow rate of cold water have important influence on heat extraction performance of HDR reservoir. Based on this, a multi-field coupling mathematical model for injection and production of HDR is established and solved by finite element method to analyze the evolutions of seepage field, temperature field and stress field in HDR reservoir. Then, high temperature production time and heat extraction rate were introduced to quantitatively evaluate the heat extraction performance of HDR reservoir under different reservoir permeability, different well type, different well spacing, different well pattern and different injection flow rate. The research results show that different reservoir permeability has little influence on the heat extraction performance of HDR reservoir. Comparing the vertical well production system with the horizontal well production system, horizontal well production system has longer high temperature production time, and vertical well production system has higher heat extraction rate. The greater the well spacing and injection flow rate, the better the heat extraction performance of HDR reservoir. The heat extraction performance of the well pattern is not necessarily better than that of the one-injection and one-production well pattern, the heat extraction performance of the one-injection two-production well pattern and the two-injection one-production well pattern is worse than that of the one-injection one-production well pattern, and the heat extraction performance of the four-injection one-production well pattern and the one-injection four-production well pattern is better than that of the one-injection one-production well pattern. The research results can provide a theoretical basis for the formulation of economic and reasonable HDR development program and working system, and realize efficient utilization of HDR reservoir.