The effect of salt on the evolution of a subsalt sandstone reservoir in the Kuqa foreland basin, western China
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ORIGINAL ARTICLE
The effect of salt on the evolution of a subsalt sandstone reservoir in the Kuqa foreland basin, western China Hai Wu1 · Mengjun Zhao1 · Qingong Zhuo1 · Xuesong Lu1 · Long Wang2 · Weiqiang Li1 · Ya Deng1 Accepted: 29 May 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract 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. Keywords Salt · Porosity · Kuqa · Diagenesis · Basin modeling · Sandstone reservoir · Brine
Introduction Giant oil and gas fields throughout the world are closely related to salt strata in the sedimentary basin (Halbouty 1979; Volozh et al. 2003; Warren 2006; Wu et al. 2016a). Although salt constitutes less than 2% of the world’s sedimentary rocks, one-half of the world’s largest oilfields are sealed by salt, and the other half are sealed by shales (Grunau 1987). Kirkland and Evans (1981) argued that salt overlies or seals carbonates containing an estimated 50% of the world’s known total petroleum reserves. The exemplary ability of salt to act as seals for large hydrocarbon columns is clearly seen in the Middle East, where Ghawar, the world’s largest oil field, is sealed by bedded salt of the Arab Formation and the overlying strata (Warren 2006). The sealing feature is among the best characteristics, since the * Hai Wu [email protected] 1
Research Institute of Petroleum Exploration & Development, PetroChina, Beijing 100083, China
Research Institute of Exploration and Development, PetroChina Changqing Oilfield Company, Xi’an 710018, China
2
extremely low permeability and porosity of salt effectively prevents hydrocarbon dissipation. However, some other salt characteristics, such as the strong ductility, could have a large influence on hydrocarbon migration and accumulation, causing the formation of favorable prospects in the suprasalt, subsalt, intrasalt and flank areas. Hydrocarbon migration, trap formation, source rock thermal evolution and re
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