The Genesis and Prospecting Significance of High-sulfur Gas Condensates in the Deep Dolomite Reservoirs Beneath Gypsum Rocks: A Case Study of the Cambrian Reservoir in Tarim Basin

Abstract

Comprehensive two-dimensional gas chromatography (GC×GC-TOFMS) was used to detect recently discovered condensates in the Cambrian dolomite reservoir beneath gypsum rocks of Tarim Basin. It was found that the thioadamantane and dibenzothiophene compounds are rich in the dolomite reservoirs, which indicates that the gas condensates have undergone hydrocarbon charging with TSR genesis. Based on the contents of SO42− and Mg2+ in the formation water of the Well ZS-1 reservoirs, the dolomite reservoirs and gypsum caps of intraplatform tidal flat facies sediments have been proven to be an effective geological combination to provide sulfate contact-ion pairs for TSR initiation. Compared with typical high-sulfur gas reservoirs with TSR throughout the world, the TSR extent in the Lower Cambrian dolomite reservoirs of ZS-1 is lower, and the liquid hydrocarbons in the Lower Cambrian of Well ZS-1 at the buried depth close to 7,000 m have not intensively cracked. Therefore, it is speculated that abundant cracking gas may occur in deeper slopes and basins (about 9,000 m) with high content of H2S and CO2. It is also revealed that deep dolomite reservoirs beneath gypsum rocks are the actual geological conditions for the accumulation and preservation of secondary H2S-bearing gas condensates.