Reserve utilization evaluation model for tight gas well based on low-velocity non-Darcy seepage

In the depletion production process of tight gas wells, the decline in formation pressure leads to a gradual reduction in the production pressure gradient from the near-well region to the far-well region. At the same time, the impact of low-velocity non-Darcy seepage on production intensifies. These phenomena pose challenges to accurately assessing reserve utilization. In this study, laboratory experiments were conducted to investigate the phenomenon of low-velocity non-Darcy seepage of gas under varying pore pressures in tight, water-bearing rocks. Using fractured horizontal wells as a case study, an evaluation model of reserve utilization founded on dual-media seepage characterization was developed. The variation in reserve utilization and recovery percentage within the production range during depletion are quantitatively depicted, and the impact of different stimulation measures is probed. The results indicate that: (1) Incorporating low-velocity non-Darcy seepage into the motion equation allows for a more precise description of the nonlinear variation characteristics in gas flow relative to pressure differences. Consequently, the established numerical simulation model can assess dynamic reserve utilization with higher accuracy. (2) During the progression of single-well depletion production, the scope of exploited reserves expands; however, this expansion may cause inadequate reserve control. The recovery percentage within the producing range initially exhibits an upward trend and subsequently decreases. At the point where gas-well mining attains its maximum recovery factor, the recovery percentage within the producing range decreases by more than 6%. (3) From the perspective of enhancing the recovery factor of reserve utilization, the significance of stimulation measures can be ranked in the following order: reducing fracture spacing > increasing fracture half-length > improving fracture conductivity > raising bottom-hole flowing pressure. While lowering the bottom-hole flowing pressure and extending the abandonment production condition can increase reserve utilization and cumulative production, they simultaneously decrease the recovery percentage of reserves. Artificial fracturing enhances both the producing geological reserves and the recovery factor of a single well, making it the primary approach for improving the production efficiency of tight gas wells.