Experimental Study on Temperature Field Monitoring Methods During Gas Discharge in Coal Seams

The evolution of the coal seam temperature field is the key factor affecting gas extraction efficiency during heat injection, but its change law under different drilling layout schemes and heat injection methods is not clear, and achieving real-time monitoring is difficult. In order to simply and quickly understand underground temperature field change, we conducted an experimental study of the temperature–resistivity correlation law; we based our study on the theory that rock resistivity changes accordingly with temperature. To study the relationship between rock resistivity and temperature, both indoor and outdoor experiments were performed. Multiple sets of rock sample heating experiments were conducted indoors on sandstone, mudstone, coal, and tuff, and a regression equation for the relationship between temperature rise and resistivity change was established. In situ heating experiments were conducted on mudstone rock masses at an underground field test site. Special geophysical equipment was used to obtain rock resistivity data corresponding to each temperature change stage. By processing and analyzing the obtained data, the actual situation of in situ saturated rock resistivity changes during temperature increase can be understood. According to the experiments, after a temperature increase of 20 °C, the resistivity of the rock decreases to approximately 80% of its initial level. After the temperature increases by 40 degrees, resistivity decreases to approximately 70% of the initial value. After a temperature increase of 70 degrees, it decreases to less than 50% of the initial resistivity. The results of indoor and outdoor in situ experiments show that by using electrical geophysical equipment to monitor changes in the electrical resistivity of rock masses, it is possible to understand the temperature change areas of underground rock masses in a timely manner. This study provides basic data for the real-time monitoring of changes in underground coalbed methane (CBM) temperature fields, which is expected to improve the efficiency of CBM mining by guiding and optimizing the drilling layout scheme and heat injection mode.