Commingling production of deep coal-measure gas through hydraulic fracturing: Propagation patterns of induced fractures and their determinants

ObjectiveThe commingling production of coal-measure gas represents a pivotal approach to enhancing the single-well production of unconventional gas in China. However, coal-measure gas reservoirs exhibit distinctly different material compositions and physical properties, leading to uncertainty of the propagation modes and developmental degrees of fractures in different reservoirs during the hydraulic fracturing of coal-measure gas reservoirs subjected to commingling production. Therefore, effectively coordinating the stimulation of multiple reservoirs for multi-gas commingling production is crucial for minimizing production costs and maximizing production capacity. Methods This study investigated the Linxing block along the northeastern margin of the Ordos Basin as an example to analyze the geologic and engineering factors influencing the commingled fracturing performance of coal-measure gas reservoirs. Utilizing numerical simulations, this study explored the propagation modes of fractures in various reservoirs. Accordingly, it proposed suggestions for commingled hydraulic fracturing in the Linxing block. Results The results indicate that an increase in the differences in the minimum horizontal in-situ stress and tensile strength between reservoirs and carriers, as well as an increase in the injection rates and viscosities of fracturing fluids, contributed to increased fracture heights and widths. Higher values of these parameters corresponded to enhanced fractures' capacity to penetrate strata. The minimum horizontal in-situ stress of strata and the viscosity of fracturing fluids primarily influenced the fracture widths of reservoirs. Specifically, a higher relative minimum horizontal in-situ stress of strata or a lower viscosity of fracturing fluids resulted in narrower fractures. Additionally, changes in the differences in modulus of elasticity and Poisson's ratio between reservoirs and barriers produced minimal impacts on the overall fracturing performance. Nevertheless, an increase in the difference in modulus of elasticity reduced the time for fractures to penetrate strata, enabling them to reach their ultimate heights more rapidly. Conclusions Based on the above results, this study proposes a scheme for selecting the optimal reservoirs and production recommendations for commingling production of coal-measure gas reservoirs in the Linxing block. Specifically, commingled fracturing should be preferentially conducted for reservoirs with the minimum horizontal in-situ stress differences of 0‒4 MPa and tensile strength differences exceeding 4.5 MPa between reservoirs and barriers. Furthermore, it is recommended that the injection rates of fracturing fluids should be greater than 4 m3/min to achieve more efficient resource development.