Li Lin, Yang Daiyan, Liu Wei, Zhang Xiong, Zhao Lingyun, Zhu Xuanshi
State Key Laboratory of Coal Mine Disaster Dynamics and Control, Chongqing University, Chongqing 400044, China.
School of Resources and Safety Engineering, Chongqing University, Chongqing 400044, China.
ACS Omega. 2022 Aug 20;7(34):30197-30207. doi: 10.1021/acsomega.2c03304. eCollection 2022 Aug 30.
It is of great significance to study the evolution law and change characteristics of the porosity and permeability of coal under cyclic disturbance to efficiently exploit coal-bed methane (CBM). In this paper, the GCTS rock mechanics experimental system is applied, the unsteady gas seepage test under cyclic loading and unloading is carried out with high-grade coal samples from Zhijin County, Guizhou Province, as the research object, and the mathematical formula of the dynamic change of porosity during loading and unloading is established. The results show that (1) the porosity and permeability parameters of coal are negatively correlated with confining pressure, and all decrease with the increase in confining pressure; (2) the change rate of the porosity and permeability of bedding coal decreases gradually with the increase in stress, and the porosity and permeability under high stress decrease gradually with the increase in cycle times; (3) during cyclic loading and unloading, the permeability loss ( ) of coal mainly occurs in the first loading (>90%), and gradually decreases with the increase in cyclic times; (4) under the same test conditions, the evolution law of the porosity and permeability of parallel bedding coal and vertical bedding coal is similar but the stress sensitivity of vertical bedding coal is higher; (5) the circumferential strain of parallel bedding coal is higher than that of vertical bedding coal, and the porosity change and permeability loss show a specific bedding effect; and (6) under the action of cyclic stress, the change of strain-permeability of coal is abnormal after it is destroyed. With the increase in strain before the sample is destroyed, the permeability drops sharply, and after the sample is destroyed, the strain decreases and the permeability never recovers. The research results can provide favorable theoretical guidance and technical support for pressure relief exploitation of coal-bed methane, such as multibranch horizontal wells.
研究循环扰动下煤体孔隙度和渗透率的演化规律及变化特征对煤层气（CBM）的高效开采具有重要意义。本文应用GCTS岩石力学试验系统，以贵州省织金县的高煤级煤样为研究对象，进行了循环加卸载下的非稳态瓦斯渗流试验，并建立了加卸载过程中孔隙度动态变化的数学公式。结果表明：（1）煤体的孔隙度和渗透率参数与围压呈负相关，均随围压的增大而减小；（2）层状煤的孔隙度和渗透率变化率随应力的增大而逐渐减小，高应力下的孔隙度和渗透率随循环次数的增加而逐渐减小；（3）循环加卸载过程中，煤体的渗透率损失（ ）主要发生在第一次加载时（>90%），且 随循环次数的增加而逐渐减小；（4）在相同试验条件下，平行层理煤和垂直层理煤的孔隙度和渗透率演化规律相似，但垂直层理煤的应力敏感性更高；（5）平行层理煤的环向应变高于垂直层理煤，孔隙度变化和渗透率损失呈现出一定的层理效应；（6）在循环应力作用下，煤体破坏后应变-渗透率变化异常。在样品破坏前，随着应变的增加，渗透率急剧下降，样品破坏后，应变减小，渗透率不再恢复。研究成果可为煤层气多分支水平井等卸压开采提供良好的理论指导和技术支持。
