Remaining reserve distribution simulation and development trend of multi-branch horizontal wells in high development coalbed methane blocks

The accurate prediction of remaining coalbed methane (CBM) reserves is crucial for optimizing production in highly developed blocks. This study establishes an integrated workflow, combining geological modeling and numerical simulation, to evaluate residual gas distribution in the Sanjiao Block of the Ordos Basin, a typical CBM field with a dense network of multi-branch horizontal wells. Results demonstrate that well productivity is initially controlled by the pressure decline rate during the early drainage stage, while it becomes more sensitive to coal thickness, gas content, and permeability during the late stage. Through history matching and reservoir parameter inversion, the well-controlled area for individual multi-branch horizontal wells was calibrated to be between 0.20 and 0.90 km². A type curve for pressure decline was subsequently constructed, enabling a reliable production forecast for the next decade. Simulation results indicate a drained area of 15.61 km², with the remaining undrained area and reserves estimated at 4.39 km² and 502 million cubic meters, respectively. This study identifies three critical factors governing prediction accuracy: the detailed characterization of reservoir heterogeneity, robust production history matching grounded in geological reality, and appropriate drainage system design. Future efforts should focus on micro-scale reservoir modeling integrating seismic and experimental data, alongside the development of standard pressure decline curves from field production data, to enhance the assessment of remaining CBM reserves in mature fields.