Experimental Study on Damage Evaluation of Working Fluid Invasion in Tight Sandstone Gas Reservoirs

The scientific evaluation of the damage caused by working fluid invasion in tight sandstone gas reservoirs is critical for optimizing drilling design, fracturing fluid systems, and construction design. This study focused on the tight sandstone core of the Qingshimao gas field in the Ordos Basin. A set of experimental methods and equipment were designed to facilitate the visual monitoring and quantitative evaluation of the reservoir damage caused by working fluids. Systematic evaluation experiments were conducted to analyze the extent of reservoir damage caused by working fluid invasion under varying pore pressure and permeability conditions. The results show the following: (1) As permeability increases, the real-time invasion flow rate rises, and the invasion rate accelerates. Meanwhile, as pore pressure increases, the real-time invasion flow rate decreases, and the invasion rate slows down. (2) The core’s fluid saturation after working fluid invasion exceeds 70%, with permeability damage reaching 95% or higher. (3) At the same reservoir pore pressure, cores with permeability ranges between 0.1 × 10−3 μm2 and 1 × 10−3 μm2 exhibit higher fluid-phase saturation and greater invasion damage. For cores with similar permeability, the higher the pore pressure, the higher the invasion-phase saturation, and the greater the extent of invasion damage. The research results provide certain guiding significance for evaluating the extent of the damage caused by working fluid invasion in tight sandstone gas reservoirs and achieving efficient gas reservoir development.