The effect of salt on the evolution of a subsalt sandstone reservoir in the Kuqa foreland basin, western China

Two sets of thick salt have developed in the Kuqa foreland basin, which has a great influence on the evolution of subsalt reservoirs. The abnormal favorable reservoirs, developed at a depth of approximately 4000–5500 ms, was several hundred meters from the bottom of the salt body based on the drilling data. The study was carried out to understand the formation of the favorable subsalt reservoirs based on the techniques of formation water salinity analysis, scanning electron microscopy (SEM) and cast thin section analysis. The results showed that during the first stage, the high-salinity formation water began to infiltrate and crystallized in the pores after the salt deposition, causing the decrease in the porosity. During the second stage, the formation water salinity decreased for the groundwater activities, which caused dissolution of the salt in the pores, a favorable subsalt reservoir was formed. During the third stage, hydrocarbons were charged and accumulated in the favorable subsalt reservoir. The high heat conductivity characteristic of the salt cooled the subsalt reservoir, which was also helpful for the forming of the favorable reservoir.