According to the fluorescence characteristics of hydrocarbon inclusions under the microscope, the interpenetration relationship with the occurrence veins, and the homogenization temperature, the hydrocarbon inclusions developed in the Cambrian-Ordovician reservoir in Yingmian 7 area can be divided into four periods, which correspond to four hydrocarbon accumulation events respectively. The periods of accumulation determined by the analysis of homogenization temperature and burial history are as follows: late Caledonian to early Hercyian low mature heavy oil filling, late Hercyian medium mature normal oil filling, early Himalayan high mature light oil filling and late Himalayan over mature natural gas filling. Among them, periods of I, II hydrocarbon inclusions distribution range is limited, only visible in part of the wells in Yingmai 7 area; periods of III, IV hydrocarbon inclusions in Yingmai 7 area are widely distributed, which reveals the Himalayan period of the two-stage oil and gas filling on the reservoir formation.
The lower Paleozoic area in Tarim Basin is the key field of deep oil and gas exploration, and the lower Cambrian source rock is the focus of current research. However, due to the deep burial depth, there are few samples of Lower Cambrian source rocks revealed by drilling. The lower Cambrian source rocks are widely exposed in the northwest of the basin, which provides a good opportunity for the study of source rocks. In this paper, the organic geochemistry of three sections and a shallow drill sample from Aksu Area in the northwest and Kuruktag area in the northeast of the basin has been systematically analyzed. The total organic carbon (TOC), bitumen content and maturity of source rocks are studied. The organic carbon content of the lower Cambrian source rocks in the Keping area of the northwest basin ranges 1.49%-14.07%, and the content of bitumen ranges 7.73-24.53 mg / g • TOC. However, the organic carbon content of the lower Cambrian outcrop samples in the Sugetebulake section ranges from 0.93% to 7.90%, and the soluble organic matter content ranges from 0.73 to 5.89 mg / g • TOC. The TOC of Lower Cambrian source rocks in Yardang mountain area of northeast basin is low, ranging from 0.75% to 1.42%, and the content of bitumen is between 2.97-3.94 mg / g • TOC. In terms of organic matter abundance, the Cambrian source rocks developed in gentle slope facies are better than those in deep-water shelf facies. The measured reflectance (Ro%) of Shairik shallow drilling samples is between 1.0% - 1.7%, with an average of 1.45%. The Ro% of Sugatebulak samples is between 1.4%-1.75%, with an average of 1.55%, indicating that the overall maturity of the source rocks in the northwest is in the condensate wet gas stage. The measured reflectance of the Cambrian source rocks in the Yardangshan and Kuruktag sections in the northeast of the basin is between 1.5-2.5% RO, with an average of 1.75% ro. The overall maturity of the source rocks in the northeast of the basin is relatively higher, suggesting a wet gas stage.
Hydrocarbon migration patterns and pathways were studied on the basis of three-dimensional seismic interpretation, drilling, geochemistry, production performance, and other data. Using these findings, the main factors controlling hydrocarbon migration and accumulation in the Lower Paleozoic carbonate rocks of the Tazhong Uplift were discussed. The spatiotemporal relationship between the hydrocarbon kitchens and pathway systems of the Tazhong Uplift and the spatial pattern of pathway systems were considered the main factors causing differences in hydrocarbon enrichment. Results also revealed that the Lower Paleozoic carbonates of the Tazhong Uplift have two hydrocarbon accumulation systems (inside and outside the source rocks). For the accumulation system within the source rocks, hydrocarbon migration and enrichment are vertically differentiated. Middle Cambrian gypsum salt rocks serve as the boundary, above which thrust and strike-slip faults mainly allow vertical transport of hydrocarbons. A multistage superposition pattern of strike-slip faults controls the differences in hydrocarbon enrichment on the periphery of the fault zone. Beneath the gypsum-salt rocks, hydrocarbon migration and enrichment is controlled by the topography of paleostructures and paleogeomorphology. For the hydrocarbon accumulation system outside the source rocks, hydrocarbon migration and enrichment are restricted by the layered pathway system, and the topography of the paleostructures and paleogeomorphology is the key factor controlling hydrocarbon enrichment. The Tazhong No. 1 Fault is the main vertical pathway system in the area underlain by no source rocks, and hydrocarbons are enriched at the periphery of the Middle-Lower Cambrian and No. 1 Fault Zone.
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