Formation mechanisms and enrichment patterns of high-sulfur gas in the Amu Darya Basin of Central Asia
Large and giant high-sulfur gas reservoirs have been discovered in the pre-salt Jurassic carbonate rocks of the Amu Darya Basin in Central Asia with high H2S contents in natural gas and quite complicated gas distribution.To further improve the exploration and development benefit of high-sulfur gas reservoirs in this area,this paper comprehensively studies the geological characteristics,spatiotemporal distribution and natural gas compositions of these high-sulfur gas reservoirs,analyzes the types and origins of high-sulfur gas reservoirs,and summarizes the enrichment patterns of high-sulfur gas.The following results are obtained.First,the H2S content in the Amu Darya Basin is closely related to the deposition and diagenesis of Upper Jurassic anhydrite.According to the source of H2S in natural gas,high-sulfur gas reservoirs can be divided into three types,i.e.,in-situ generation,allochthonous generation and mixed generation,among which,in-situ generation is dominant.Second,the in-situ generated high-sulfur gas reservoirs can be subdivided into the gypsum interbedded with limestone gas reservoir in intraplatform-platform margin facies zones,the high-energy reef-shoal gas reservoir in platform marginal slope zones,and the fault controlled gas reservoir in platform marginal slope-basin facies zones.The allochthonous generated high-sulfur gas reservoirs can be subdivided into the lateral migration and accumulation gas reservoir and the vertical migration and accumulation gas reservoir.Third,the enrichment degree of high-sulfur gas is controlled by hydrocarbon generating depressions and carbonate sedimentary facies zones,and the highest enrichment degree occurs in the carbonate platform margin facies zones.The faults connecting source rocks can further promote the accumulation and enrichment of high-sulfur gas,and inherited structures with large paleo-uplift background in the hydrocarbon generating depressions are the most favorable exploration targets.It is concluded,by understanding the formation mechanisms and enrichment patterns of high-sulfur gas,that exploration shall focus on the pre-salt Jurassic high-sulfur carbonate gas reservoirs with basement paleo-uplifts and large fault zones in the hydrocarbon generating depressions of the Amu Darya Basin.
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维普
