Study on stress sensitivity of coal reservoirs under different temperatures and effective stresses

Pei Shenquan; Zhang Miao

doi:10.19896/j.cnki.mtkj.2025.06.015

Abstract：One of the key challenges in the development of deep coal-measure gas reservoirs lies in the complexity of permeability dy-namics under high temperature and high pressure conditions.To explore the influence of temperature and effective stress on the stress sensitivity of coal reservoirs,the overburden permeability experiments were conducted under different temperatures(30,50,70℃)and different confining pressures(5,10,15,20,25 MPa)with the No.3 coal seam in Yushe-Wuxiang block of Qinshui coalfield as the re-search object.The results show that the permeability of No.3 coal seam decreases exponentially with the increase of effective stress and exhibits obvious stage characteristics:when the effective stress is below 8 MPa,the permeability drops sharply(with the strongest stress sensitivity);thereafter,as the effective stress continues to increase,the permeability attenuation rate decreases significantly and the sen-sitivity weakens.With the increase of temperature,the permeability of No.3 coal seam shows a decreasing trend:when the effective stress is less than 15 MPa,the decrease in permeability follows the order of 70℃>50℃>30℃;when the effective stress exceeds 15 MPa,the decrease in permeability follows the order of 50℃>30℃>70℃as temperature increases,indicating that the controlling effect of effective stress is stronger than that of temperature.The damage rate of coal sample permeability exhibits a three-stage evolu-tion pattern of"rapid increase-decreasing growth rate-stabilization"with the increase in effective stress.As temperature increases(30℃→50℃→70℃),the permeability damage rate increases from 53.8％to 72.7％.Under the same effective stress,the permeability damage rate of coal samples shows a decreasing trend,but the increase laws of damage rate varies across different stress ranges:when the effective stress is below 15 MPa,the permeability damage rate follows the order of 70℃>50℃>30℃;when the effective stress is greater than 15 MPa,the permeability damage rate follows the order of 50℃>30℃>70℃.The dimensionless permeability of No.3 coal seam decreases exponentially as effective stress increases.When the effective stress is less than 15 MPa,the decrease in dimensionless permeability follows the order of 30℃>50℃>70℃;when the effective stress exceeds 15 MPa,the decrease follows the order of 70℃>50℃>30℃.This indicates that increasing temperaturecan inhibit its decrease,but the dominant role of effective stress is significant.