Large-scale physical simulation of flow behavior in Kelasu ultra-deep fractured low-porosity sandstone gas reservoirs

The ultra-deep fractured low-porosity sandstone gas reservoirs in the Kuqa Depression of the Tarim Basin exhibit complex characteristics, including high temperature, high pressure, significant in-situ stress, multi-scale fractures, and strong aquifer activity. The development of these reservoirs is challenged by rapid water invasion, which causes severe production declines. Conventional experiments fail to adequately simulate the coupled flow between the in-situ matrix and fractures. This study developed a high-temperature, high-pressure large-scale physical simulation platform and a methodology for preparing large rock samples with complex fractures. Using this platform, we conducted single-phase and gas-water two-phase flow experiments under in-situ conditions. The key results indicate that during single-phase depletion, cumulative gas production rapidly reaches a quasi-steady state, confirming the hierarchical flow and coupling from “large fracture” to “small fracture” to “matrix”. The matrix’s gas supply capacity diminishes with decreasing pressure, exacerbating the supply-production imbalance. Constant-volume bottom water experiments reveal that when fracture water saturation exceeds a critical threshold, the matrix gas supply abruptly declines due to “water-sealed gas”. Continuous fracture drainage and pressure reduction can partially alleviate this sealing and restore some gas supply, although recovery remains limited. Experiments under different management strategies demonstrate that higher production rates and larger water-to-gas volume ratios lead to lower cumulative gas production before water sealing, higher abandonment pressures, greater challenges in post-sealing recovery, and consequently, lower ultimate recovery. These findings provide critical insights for optimizing development strategies in ultra-deep fractured low-porosity sandstone gas reservoirs.