Offshore low-permeability to tight sandstone gas reservoirs are characterized by complex pore-throat systems and strong reservoir sensitivity, yet the mechanisms controlling sensitivity and its impact on gas-well deliverability remain poorly understood. In this study, reservoir mineral composition and microscopic pore-throat structure were characterized using X-ray diffraction (XRD) and mercury injection experiments. Core-based sensitivity tests were then performed to quantitatively evaluate the damage caused by different sensitivity types and to identify their controlling factors. Based on the experimental results, gas-well deliverability models under different sensitivity conditions were established to predict productivity and absolute open flow (AOF). The results show that under a confining pressure of 20 MPa, permeability decreases by 56%–82.8%, with only 28%–33% recovery after unloading. Lower injected-water salinity induces pronounced water sensitivity: permeability decreases by about 20%–30% after half-salinity formation water injection and by 60%–69% after deionized water injection. Increasing flow velocity causes velocity sensitivity, with a maximum damage rate of 34%–45%. Sensitivity variations are mainly controlled by pore-throat structure and mineral composition. Samples with high clay content and fine pore throats show severe permeability loss, whereas cores with broader pore-size distributions exhibit stronger resistance to water disturbance. Deliverability simulations indicate that reservoir sensitivity reduces AOF by about 14%, demonstrating a clear suppressive effect on gas-well productivity. In addition, productivity and AOF increase with improved pore-throat structure, whereas higher mineral content exerts a negative effect.
Jie et al. (Fri,) studied this question.