Types of pre-salt carbonate gas reservoirs and hydrocarbon enrichment factors of Amu Darya right bank area in Turkmenistan

Hydrocarbon resources in the Middle-Upper Jurassic Callovian-Oxfordian carbonate rocks are abundant; however, research on the distribution law of hydrocarbon is relatively backward. Through the study of typical gas reservoirs, analysis of the type of hydrocarbon reservoirs and discussion of the major reasons for high hydrocarbon output, we determined that there are three main types of pre-salt gas reservoirs in carbonate rocks:structural, lithologic and structural-lithologic compound gas reservoirs. Additionally, there are five minor gas reservoirs:anticline, faulted anticline, thrust faulted anticline, reefs and structural-lithologic gas reservoirs. We also discovered that Hercynian basement paleo-uplift controlled the formation of large gas fields and Himalayan extruded tectonic movement formed thrust faulted hydrocarbon accumulation zones. The abundance of gas was controlled by sedimentary facies belts and good seal provided by salt-gypsum cover contributing to the formation of faulted anticline gas reservoirs. The coincidence of large anticline structures and high energy reef beach body was the major controlling factor for the enrichment of natural gas in the west Zarzhu terrace. The coincidence of thrust faulted anticlinal structural traps and large scale fissure type reservoirs is the main reason for the enrichment and high yield of natural gas in the east Bieshikent Depression and Jisaer folded uplift zone.