Hydraulic Fracturing Simulation Experiments and Fracture Characterization of Coal Reservoirs in the Dahebian Syncline.

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 m3. 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.