Peng Shoujian, Fang Zhiming, Shen Jian, Xu Jiang, Wang Geoff
State Key Laboratory of Coal Mine Disaster Dynamics and Control, Chongqing University, Chongqing, 400044, China.
School of Chemical Engineering, The University of Queensland, Brisbane, QLD 4072, Australia.
Sci Rep. 2017 Oct 30;7(1):14337. doi: 10.1038/s41598-017-14678-1.
The cleat compressibility of coal is a key parameter that is extensively used in modeling the coal reservoir permeability for Coal Bed Methane (CBM) recovery. Cleat compressibility is often determined from the permeability measurement made at different confining pressures but with a constant pore pressure. Hence, this parameter ignores the sorption strain effects on the cleat compressibility. By using the transient pulse decay (TPD) technique, this study presents the results from a laboratory characterization program using coal core drilled from different bedding directions to estimate gas permeability and coal cleat compressibility under different pore pressures while maintaining effective stress constant. Cleat compressibility was determined from permeability and sorption strain measurements that are made at different pore pressures under an effective stress constant. Results show that the cleat compressibility of coal increases slightly with the increase of pore pressure. Moreover, the cleat compressibility of Sample P (representing the face cleats in coal) is larger than that of Sample C (representing the butt cleats in coal). This result suggests that cleat compressibility should not be regarded as constant in the modeling of the CBM recovery. Furthermore, the compressibility of face cleats is considerably sensitive to the sorption-induced swelling/shrinkage and offers significant effects on the coal permeability.
煤的割理压缩性是一个关键参数，在煤层气（CBM）开采的煤储层渗透率建模中被广泛应用。割理压缩性通常由在不同围压但孔隙压力恒定的情况下进行的渗透率测量来确定。因此，该参数忽略了吸附应变对割理压缩性的影响。通过使用瞬态脉冲衰减（TPD）技术，本研究展示了一个实验室表征项目的结果，该项目使用从不同层理方向钻出的煤芯，在保持有效应力恒定的情况下，估计不同孔隙压力下的气体渗透率和煤割理压缩性。割理压缩性由在有效应力恒定的情况下，在不同孔隙压力下进行的渗透率和吸附应变测量来确定。结果表明，煤的割理压缩性随孔隙压力的增加而略有增加。此外，样品P（代表煤中的面割理）的割理压缩性大于样品C（代表煤中的端割理）。这一结果表明，在煤层气开采建模中，割理压缩性不应被视为常数。此外，面割理的压缩性对吸附引起的膨胀/收缩相当敏感，并对煤的渗透率有显著影响。
