Dynamic evolution of key reservoir parameters in coal seam horizontal wells during drainage: implications for production optimization

Surface drainage of low-permeability coal seams via horizontal wells is critical for safe mining in high-gas outburst mines, but limited understanding of reservoir parameter evolution obscures gas decline and optimization mechanisms. Focusing on the Xintian Coal Mine in Western Guizhou, this study integrated experiments and simulations to invert pore pressure and gas content evolution, diagnose conventional drainage failure, and propose optimization principles. In Well A-1, excessively rapid pore pressure decline during early drainage stages (39.5% drawdown in first 100 days at 14.96 kPa/d) may have induced stress sensitivity, the Jamin effect, and coal fines migration, causing irreversible permeability damage in the strongly stimulated zone. Thus, the desorption area was only 78.7% of the pressure drop area, leaving much adsorbed gas unused. By implementing staged pressure decline control and restraining casing pressure, Well B-1 achieved a pressure drop area (0.67 km2) close to its desorption area (0.65 km2), with 9.8% and 35% expansions in pressure drop and desorption areas. The key to optimization is refined single-phase drainage stage management, realizing synergy of “pressure node identification, staged rate control, dynamic matching of fluid supply capacity” to ensure smooth flow transitions. This principle provides a reference for similar conditions in coal mining areas.