Study on the Damage Mechanism of Rock Around Wells Subjected to Impact Loading

ABSTRACT: To investigate the rock damage characteristics in the vicinity of a wellbore under mid-to-high temperature reservoirs with varying impact parameters, this study conducts bit impact rock-breaking experiments under high-temperature and high-pressure conditions. Standard core samples are drilled at different positions on the wellbore wall to test and obtain the distribution pattern of microcracks in the surrounding rock and to characterize their microdamage attributes. Numerical simulations are then carried out to further analyze the damage patterns to rocks near the wellbore caused by impact drilling. The results demonstrate that impact drilling can cause damage to rocks near the wellbore, with the damage becoming more severe and the microcracks more densely packed as one approaches the wellbore wall. The temperature of the reservoir significantly influences the effectiveness of impact drilling. Different phases of impact also affect the stress state and damage characteristics of the rocks, particularly during the unloading phase, where the bottomhole and surrounding rocks generate more fissures. 1. INTRODUCTION As an important clean and renewable energy source, geothermal energy has the characteristics of low carbon, environmental protection, stability and high efficiency. It is one of the most competitive renewable and clean energy sources (Yu et al., 2018). Geothermal resources are mainly divided into open heat extraction and closed heat extraction according to different development methods. Studies have shown that the former is superior to the latter in terms of economy and heat extraction efficiency (Wang et al., 2019). For open heat extraction, formation permeability is an important factor to determine the efficiency of heat extraction. On the one hand, the higher the formation permeability, the greater the flow rate of the fluid, the more heat it can carry, and the higher the convective heat transfer intensity, so the thermal efficiency is significantly increased. On the other hand, the currently under construction and completed water-intaking geothermal systems require tail water recharge to ensure the sustainability of heat extraction and prevent environmental pollution and land subsidence. It can be seen that improving the formation permeability has become a key link to strengthen the heat extraction effect.