Study of Simulation Method of Porosity and Permeability Parameters of Salt Deposition Reservoir Based on Phase Equilibrium Calculation

Abstract

High salinity gas reservoirs are prone to salt deposition in the middle and late stages of development, resulting in the decrease of porosity and permeability, which seriously affects the development of gas reservoirs. Therefore, it is necessary to understand the changes of reservoir porosity and permeability parameters in time. At present, the relationship between salt deposition, porosity, and permeability parameters is generally determined according to experimental data, which lacks strict theoretical basis. Therefore, based on the phase equilibrium of hydrocarbon-brine and the equation of state of porosity, a model of porosity and permeability variation considering salt deposition is established. The feasibility of the method is verified by matching the experimental data. The reservoir porosity and permeability variation under different salinity were simulated. Combined with the phase distribution, the reasons for the change of salt deposition and pore permeability parameters were analyzed. The results show that the pore permeability parameters are basically unchanged under high pressure, while the pore permeability parameters change obviously under low pressure due to the decrease of liquid water content. According to the downhole pressure and temperature changes, the reservoir porosity and permeability parameters can be monitored in real time, which provides theoretical guidance for the later gas reservoir development. During the development of high salinity reservoirs, as the temperature increases and the pressure decreases, the water gradually evaporates and the salt precipitates. It causes blockage of the flow channel, greatly affects the porosity and permeability, and causes the reservoir difficulty in maintaining normal development. Based on the theory of phase equilibrium and mass conservation of salt, the mass of precipitated salt is calculated, and the porosity and permeability change models are established. The variation of underground porosity and permeability can be determined according to the produced fluid components, so as to achieve the purpose of real-time monitoring of the properties of underground reservoirs. The change of reservoir property parameters can be controlled by controlling the production pressure. It can avoid the downhole pollution in the production process in time and effectively improve the production efficiency. It is very important to deeply understand the changing characteristics of underground reservoir properties for the subsequent formulation of a reasonable working system.