Mechanical behavior and permeability characteristics of deep coal reservoirs and their geological constraints
stress-strain, dynamic permeability, damage, permeability, deep
Resource Development and Utilization > 6. Unconventional Natural Gas Geology and Development
Draft Paper Accepted
和伟 张 / 中国矿业大学
建 申 / 中国矿业大学
可心 李 / 华北油田；山西煤层气分公司
强 黄 / 中国矿业大学
磊 杜 / 陕西煤田物探测绘有限责任公司
The mechanical behavior and permeability of deep coal reservoirs are important research directions in the development of deep coalbed methane. However, it is difficult to measure them in deep in-situ conditions and its geological constraints are unclear. In this study, the raw coal from Baode block was collected, and three-axis equipment was used to explore the change characteristics of coal mechanical behavior and permeability under different temperatures and pressures. The results show that the stress-strain curves of coal under the combined action of temperature and confining pressure are similar to the typical curve, but its stage is not obvious. In order to accurately identify the stages of coal mechanical behavior, the micro-slope method is proposed for stage division, and the whole process is divided into five stages. The permeability is closely related to the deformation stage and exhibits a U-shaped change with the increase of the axial strain, and its minimum value mostly occurs at the end of the elastic deformation. The increase of confining pressure strengthens the mechanical properties of coal, which leads to the increase of peak stress (σmax) and the prolongation of peak strain (εmax). While the temperature plays a role in weakening the coal body strength, the σmax and the εmax decrease as the temperature increases. For permeability, both confining pressure (10~30 MPa) and temperature (30~80℃) play a negative role. The initial (K0) and post-destruction permeability (Kd) of coal samples are more sensitive to changes in temperature and confining pressure, and the minimum permeability (Kmin) remained basically stable. Finally, the temperature-stress-strain-permeability model of deep coal reservoir is established. This study is expected to provide a reference for understanding the mechanical behavior of deep coal reservoirs.