High-temperature sensitivity evaluation experiment of low-permeability reservoirs based on the pressure pulse decay method

Low-permeability oil and gas reservoirs are vulnerable to damage that is difficult to remove in the process of well drilling and completion. Traditional steady-state displacement method for evaluating such damage has technical limitations such as poor applicability and low experimental efficiency. Based on the basic principle of the pressure pulse decay method, the law of upstream pressure pulse decay and its relationship with the permeability of cores are analyzed, and the damage evaluation experimental setup and method suitable for low-permeability reservoirs are established by taking the pressure pulse decay time before and after core damage as the evaluation index. Then, sensitivity evaluation experiments are performed on cores of deep low-permeability sandstone in the Bozhong sag of the Bohai Bay Basin at normal temperature and 150 °C. The results show that the pressure pulse decay time is only related to the permeability of the core when the experimental conditions are constant. The pressure pulse decay method can be used to evaluate the damage degree of the low-permeability core without permeability calculation. The experimental setup is simple and operable, avoiding the complex permeability calculation and the error caused thereby. The experimental time is far less than that of the traditional steady-state displacement method. With good repeatability, the pressure pulse decay method is well applicable to low-permeability gas reservoirs, and ultra-low to super-low permeability oil reservoirs. The high-temperature environment obviously aggravates the sensitivity damage of the reservoir. Therefore, the research on damage of deep high-temperature reservoirs and corresponding solution need to fully consider the influence of high temperature. The proposed experiment based on the pressure pulse decay method is more applicable to sensitivity evaluation of low-permeability reservoirs than the traditional method, and provides a methodological and theoretical support for finding solutions to protection of high-temperature, low-permeability reservoirs. © 2024 Natural Gas Industry Journal Agency. All rights reserved.