Wei Yuanlong, Zhao Fuping, Fu Yinlan, Zhao Lingyun, Liu Wei, Zhou Xiaozhi
Key Laboratory of Unconventional Natural Gas Evaluation and Development in Complex Tectonic Areas, Ministry of Natural Resources, Guiyang 550081, China.
Guizhou Engineering Research Institute of Oil & Gas Exploration and Development, Guiyang 550081, China.
ACS Omega. 2025 May 12;10(19):19394-19409. doi: 10.1021/acsomega.4c10461. eCollection 2025 May 20.
The coalbed methane resources in the Dahebian Syncline area of the Liupanshui coalfield, Guizhou Province, are abundant, with geological resource reserves anticipated to exceed 20 billion m. However, this region is characterized by multiple thin to medium-thick coal seams and complex regional geological conditions, which have led to unsatisfactory outcomes from previous hydraulic fracturing and coalbed methane development projects. This study selected underground coal seam cores from this area to conduct large-size physical simulation experiments on hydraulic fracturing of coal specimens. The impacts of fracturing fluid injection rate, in situ stress state, and formation depth on the effectiveness of fracturing were investigated. Additionally, the influences of various factors on fracture pressure, fracture propagation, and fracture morphology were analyzed individually. The research findings indicate the following: (1) The fracturing fluid injection rate exerts the most significant influence on the hydro-fracturing formation of coal specimens. As the injection rate increases, both fracture pressure and complexity of fractures also rise. (2) The coefficient of horizontal stress difference is another critical factor affecting the pump pressure curve and fracture morphology. An increase in this coefficient leads to greater difficulty in fracturing the coal seam, resulting in a fractured area that becomes progressively longer and narrow. (3) With increasing formation depth, the challenges associated with fracturing intensify. The pump pressure curve transitions from a stable rising pattern to one characterized by violent fluctuation, eventually shifting to a fluctuating rising trend. (4) The existence of natural fractures obviously affects pump pressure and fracture characteristics, particularly when these natural fractures are well-developed, as they notably impact the formation of complex local fractures. Consequently, it is essential to enhance the injection rate to facilitate long-distance fracture propagation, while simultaneously creating a complex local fracture network. This study provides valuable insights for designing hydraulic fracturing operations and enhancing productivity within the Dahebian Syncline as well as similar area.
贵州省六盘水煤田大河边向斜地区的煤层气资源丰富，地质资源储量预计超过200亿立方米。然而，该地区煤层多薄至中厚，区域地质条件复杂，导致以往水力压裂和煤层气开发项目效果不理想。本研究选取该地区井下煤层岩心，对煤样进行水力压裂大型物理模拟实验。研究了压裂液注入速率、地应力状态和地层深度对压裂效果的影响。此外，还分别分析了各因素对破裂压力、裂缝扩展和裂缝形态的影响。研究结果表明：（1）压裂液注入速率对煤样水力压裂形成的影响最为显著。随着注入速率的增加，破裂压力和裂缝复杂性也随之增加。（2）水平应力差系数是影响泵压曲线和裂缝形态的另一个关键因素。该系数增大导致煤层压裂难度增大，裂缝区域变得越来越长且窄。（3）随着地层深度增加，压裂难度加大。泵压曲线从稳定上升模式转变为剧烈波动模式，最终转变为波动上升趋势。（4）天然裂缝的存在明显影响泵压和裂缝特征，特别是当这些天然裂缝发育良好时，它们对复杂局部裂缝的形成有显著影响。因此，必须提高注入速率以促进裂缝长距离扩展，同时形成复杂的局部裂缝网络。本研究为大河边向斜及类似地区的水力压裂作业设计和提高产能提供了有价值的见解。
