Characteristics and main control factors of Ordovician shoal dolomite gas reservoir in Gucheng area, Tarim Basin, NW China

Abstract

Based on seismic, drilling data and experimental analysis, the characteristics and main controlling factors of shoal dolomite gas reservoir in the third member of Ordovician Yingshan Formation of Gucheng area, Tarim basin were examined. The study shows that the dolomite gas reservoir in Gucheng area is lithologic gas reservoir controlled by shoal and fault jointly, and its formation is mainly attributed to the following factors: (1) The continuously developing paleotectonic structure has been in the direction of gas migration and accumulation; (2) The large area of medium—high energy grain bank deposited in gentle slope environment is the material basis for the formation of dolomite reservoir; (3) Atmospheric water leaching and dolomitization and fluid dissolution in fault zone are the key factors for the formation of high-quality dolomite reservoir; (4) The natural gas comes from cracking of the ancient oil reservoir and hydrocarbon generation of dispersed organic matter in source rocks, and the NNE-trending strike-slip fault is the dominant channel for vertical migration of natural gas; (5) Limestone cap rocks in the first and second members of Yingshan Formation provide direct sealing for the formation of gas reservoir there. On the basis of comprehensive analysis, it is pointed out that the Gucheng area has three grain shoal zones in the third member of Yingshan Formation in nearly S-N direction, which together with seven strike-slip fault zones in NNE direction control the development of shoal dolomite gas reservoir.

Keywords

• Tarim Basin
• Gucheng area
• Ordovician Yingshan Formation
• dolomite gas reservoir
• grain shoal facies
• strike-slip fault