Wu Hongjian, Kong Xiangwei
School of petroleum engineering, Yangtze University, Wuhan, 430100, China.
Hubei Key Laboratory of Oil and Gas Drilling and Production Engineering, Yangtze University), Wuhan, 430100, China.
Sci Rep. 2025 Jan 24;15(1):3025. doi: 10.1038/s41598-025-87026-3.
Given the suboptimal physical properties and distinctive geological conditions of deep coalbed methane reservoirs, any reservoir damage that occurs becomes irreversible. Consequently, the protection of these deep coalbed methane reservoirs is of paramount importance. This study employs experimental techniques such as scanning electron microscopy, X-ray diffraction, and micro-CT imaging to conduct a comprehensive analysis of the pore structure, mineral composition, fluid characteristics, and wettability of coal seams 3# and 15# in the northern Qinshui Basin of China. The objective is to elucidate the types of reservoir damage induced by fracturing fluid intrusion along with potential contributing factors. This research is critical for ensuring safe drilling practices, effective gas injection, and efficient development strategies for coalbed methane reservoirs. The findings indicate that the mineral composition of the coal rock consists of 18.52% clay minerals, 34% quartz, and 8.98% calcite. Furthermore, hydrophilicity and natural fractures within the coal rock may lead to water-sensitivity, velocity- sensitivity, alkali- sensitivity, and acid- sensitivity damages to the coalbed methane reservoir. There exists good compatibility between fracturing fluids and both coal rock as well as formation water. The fine particles generated from hydraulic fracturing are prone to transport through the coal seam while obstructing pore throats. Thus exhibiting pronounced velocity sensitivity characteristics in this reservoir type. Coal rock demonstrates pronounced stress sensitivity. As the effective stress escalates from 2 MPa to 10 MPa, there is a marked decrease in the permeability of coal rock. With increasing effective stress, the pore structure and natural fractures within the coal rock are compressed more tightly, resulting in a diminished permeability of the coal rock. When exposed to fracturing fluid saturation, not only does the volume of these particles expand but they can also cause blockages that result in up to a 60% reduction in fracture flow capacity. These insights are vital for optimizing fracturing designs aimed at protecting reservoir integrity.
鉴于深部煤层气储层的物理性质欠佳以及独特的地质条件，任何发生的储层损害都将不可逆转。因此，保护这些深部煤层气储层至关重要。本研究采用扫描电子显微镜、X射线衍射和显微CT成像等实验技术，对中国沁水盆地北部3#和15#煤层的孔隙结构、矿物组成、流体特征和润湿性进行了全面分析。目的是阐明压裂液侵入引起的储层损害类型以及潜在的影响因素。这项研究对于确保煤层气储层的安全钻井作业、有效的气体注入和高效的开发策略至关重要。研究结果表明，煤岩的矿物组成包括18.52%的粘土矿物、34%的石英和8.98%的方解石。此外，煤岩内部的亲水性和天然裂缝可能导致煤层气储层发生水敏、速敏、碱敏和酸敏损害。压裂液与煤岩和地层水之间具有良好的配伍性。水力压裂产生的细颗粒易于在煤层中运移，同时堵塞孔隙喉道。因此，在这种储层类型中表现出明显的速敏特征。煤岩表现出明显的应力敏感性。随着有效应力从2MPa增加到10MPa，煤岩的渗透率显著降低。随着有效应力的增加，煤岩内部的孔隙结构和天然裂缝被压缩得更紧密，导致煤岩渗透率降低。当暴露于压裂液饱和状态时，这些颗粒不仅体积膨胀，还会造成堵塞，导致裂缝导流能力降低高达60%。这些见解对于优化旨在保护储层完整性的压裂设计至关重要。
