Reservoir dynamic evolution and drainage optimization in deep saturated coalbed methane of Shenfu Block

China possesses vast deep coalbed methane (CBM) resources, However, the dynamic evolution of reservoir pressure and permeability during the production process remains unclear, which restricts their efficient development. This study conducted to reveal the dynamic evolution of coal reservoir pressure and permeability under different production rates and its influence on the productivity of deep saturated CBM wells, so as to provide a theoretical basis for efficient development. Based on actual production data from deep saturated CBM vertical wells in the Shenfu Block, and considering positive and negative effects on coal reservoirs during drainage, this study utilizes reservoir pressure and permeability prediction models and derives from production dynamics to characterize the variations of reservoir pressure and permeability under different drainage rates, and analyzes their impacts on well productivity. The gas production curves of deep saturated CBM wells in the Shenfu Block can be classified into two types: decline type and stable type. The results show that the initial pressure drop rate is the key factor leading to productivity differentiation. Stable-type wells exhibit a lower initial pressure drop rate, a wider propagation range of reservoir pressure, and a permeability improvement of 5.4%, enabling sustained and efficient CBM production. In contrast, decline-type wells experience an excessively rapid initial pressure drop rate, resulting in slow reservoir pressure decline, limited permeability enhancement of only 0.9%, and a significant drop in productivity at later stages. To achieve high and stable production of deep saturated CBM wells, a strategy of "slow drainage and controlled pressure" should be adopted. It is recommended to control the bottomhole flowing pressure drop rate within 160 kPa/d during the initial production stage; appropriately increase the rate by 50-100 kPa/d during the gas production increase stage to promote gas desorption; and adjust it back to around 50 kPa/d during the later decline stage to maintain production.