The Experimental Methods to Evaluate the Fluids Sensitivity Damage of Ultra-deep and Ultra-tight Gas Reservoirs

Ultra-tight gas reservoirs are characteristic with deep buried depth, high formation temperature and strong potential fluids sensitivity damage, and the ultra-low permeability of matrix lead to the industry standard method not being applied to evaluate the formation fluids sensitivity damage. In this study, sandstone cores from ultra-tight gas layers were selected. Meanwhile, modified pressure decay method was proposed. In addition, the normal pressure decay method and modified steady-state fluid sensitivity test method were used to evaluate the water sensitive damage degree as a comparison. The results indicates that the water sensitivity damage degree obtained by the normal pressure decay method is middle to weak, the water sensitivity damage degree obtained by the modified pressure decay method is middle to strong, which is consistent with the modified steady-state fluid sensitivity test method. Moreover, the experiment time was reduced by nearly 40%. The analysis showed that the modified pressure decay method could simulate the stratum high temperature environment with the clear principle and obtained reliable result. The new method makes up for the deficiency that the normal pressure decay method cannot efficiently inject the working fluid into the core, improves the testing accuracy and shorts the experimental time, and has reference significance for the damage evaluation method of ultra-tight oil and gas reservoir.