Hydraulic fracturing response characteristics and differentiated pumping parameter optimization of coal reservoirs in the Yushe-Wuxiang block, Qinshui Basin, China

As an important unconventional natural gas resource, coalbed methane (CBM) plays a significant role in safeguarding national energy security. The Yushe-Wuxiang block, located in the central-eastern Qinshui Coalfield, is rich in CBM resources; however, its coal reservoirs are characterized by low permeability and strong heterogeneity, making hydraulic fracturing the key technology for efficient CBM development in this block. Constrained by complex reservoir geological conditions and inadequate matching between engineering parameters and reservoir conditions, the effectiveness of fracturing stimulation varies markedly across the block, and a differentiated fracturing parameter optimization system based on reservoir classification is urgently required. Taking the No. 3 coal seam, the main mined seam of the block, as the research object, this paper systematically analyzes the hydraulic fracturing response characteristics of the coal reservoirs based on field fracturing data and establishes a differentiated pumping parameter optimization system based on reservoir classification. The results show that the fracturing operation curves in the study area can be classified into three types—normal, fluctuating, and complex—corresponding to different reservoir conditions and fracture propagation patterns. The breakdown pressure of the No. 3 coal seam ranges from 20 to 62 MPa; it is influenced by burial depth but is jointly controlled by multiple factors including coal mechanical properties and natural fractures. Injection rate, proppant dosage, and fracturing fluid type are the core engineering parameters controlling fracture propagation, and all show significant correlations with sand ratio, which is adopted in this paper as an indirect indicator of fracture propagation, although this indicator is still subject to interference from artificial operational conditions. Zonation evaluation based on four key parameters—burial depth, coal thickness, brittleness index, and permeability—divides the No. 3 coal seam into nine reservoir types, and targeted pumping parameter recommendations are proposed for each type. Limited by available data, the proposed optimization scheme is an empirical scheme derived from geological and operational statistics and awaits further verification by subsequent field production data. The results provide a scientific basis for the fracturing design of CBM wells in this block.