Sensitivity Evaluation and Influencing Mechanism Analysis of Tight Sandstone in the Longtan Formation of the Western Section of the Ancient Uplift in Central Guizhou, China: A Case Study of the Agong Syncline.

Coal-measure tight sandstone gas constitutes a significant component of hydrocarbon resources in the Longtan Formation, Zhijin area. Investigation of tight sandstone reservoir sensitivity is directly pertinent to optimizing stimulation treatment design and formulating production strategies. This study systematically examines sensitivity characteristics and controlling factors of tight sandstone reservoirs in the Middle Longtan Formation, Zhijin block, employing sensitivity testing, XRD analysis, mercury injection capillary pressure (MICP) measurements, and cast thin section observation. The results indicate that these reservoirs exhibit moderate-to-weak velocity sensitivity, strong water sensitivity, weak acid sensitivity, and negligible alkali sensitivity, with a critical salinity of 70,000 mg/L. The average clay mineral content is 36.7%, with elevated Illite-smectite mixed-layer minerals and kaolinite contents identified as the principal controlling factors responsible for moderate-to-weak velocity sensitivity, strong water sensitivity, and low critical salinity, whereas elevated chlorite content accounts for weak acid sensitivity. Pore-filling cementation predominates, accompanied by elevated argillaceous cement contents, indicating weak bonding strength. During water injection and gas production, these rocks are prone to water absorption, softening, and swelling, thereby inducing sensitivity damage. A regional water sensitivity assessment chart was established accordingly. The core strategy for reservoir stimulation focuses on inhibiting clay swelling, controlling operational flow rates, maintaining formation salinity, and optimizing injected fluid compatibility, while production operations require low-rate staged commissioning combined with precise liquid-loading control to achieve long-term reservoir protection and stable gas well production. These findings demonstrate that tight sandstone reservoirs in the Longtan Formation, western Guizhou, present considerable development challenges overall; however, locally favorable zones retain certain potential for stimulation and commercial viability.