干旱区生态环境知识资源中心

China has made great process in oil and gas exploration of marine carbonate reservoirs and discovered a lot of large oil and gas fields. The Tazhong area is the main exploration and petroleum-rich area of Tarim basin. Lianglitage Formation of Ordovician was controlled by Tazhong No. I slope-break zone, and developed shelf margin reef-shoal reservoir with the character of low porosity to ultra-low porosity and low permeability, which the buried depth was between 4500 to 6500m. Reservoir formation and distribution was controlled by the factors of early high energy environment, dissolution and faulting, and the spatial distribution of effective reservoir controlled distribution of oil and gas and large-area accumulation. Through oil-source correlation, it’s showed that the hydrocarbon of reef-shoal reservoir in Lianglitage Formation mainly originated from Upper Ordovician source rock and Cambrian source rock; in which natural gas mainly came from cracking gas of Cambrian oil, and infill injected inward along Tazhong No. I slope-break zone fault. By the analysis of accumulation process, it’s confined there were three main accumulation periods in Tazhong area, the first accumulation period was Late Caledonian, which the oil and gas was mainly from Cambrian-Lower Ordovician’s source rock, but Early Hercynian tectonic movement broke the oil and gas accumulated in Caledonian period seriously. The second accumulation period was Late Hereynian, which was the most important accumulation period in Tazhong area, oil and gas was mainly originated from Middle and Upper Ordovician source rock. The third accumulation period was Late Himalayan, under the effect of Kuche foreland thrust, the platform subsidented quickly, with the rapidly increasing of depth. During Late Himalayan period, the crude-oil-cracking gas which generated from Cambrian reservoir accumlated in shallow Ordovician along the deep fault, transformed the oil reservoirs into condensate gas reservoirs with in large-scale distribution.