LATE CENOZOIC TECTONIC AND STRUCTURAL CONTROLS ON THE HYDROCARBON CHARGE HISTORY AND DISTRIBUTION PATTERNS IN THE SOUTHERN JUNGGAR THRUST BELT, XINJIANG, NORTERNWESTERN CHINA

Regional studies indicate that the intense Cenozoic tectonism at the north margin of Tianshan initiated at about 10Ma~7Ma BP, associated with intense tectonic deformation, led to the formation of three thrust belts at the south margin of Junggar basin. The time of intense deformation is much younger than that of southern Tianshan, suggesting tectonic deformation propagated from the southern Tianshan to the northern Tianshan, due to the India-Asia collision. The intense deformation of Late Cenozoic resulted in relatively gentle deformation at western Uromuqi-Qigu anticline and widespread tectonic deformation transporting and retrogressing from the south to the north. Integrated with surface dip angle measurement data, seismic refection profiles, drilling and dip angle logging data, according to the fault-related fold theory, structural profiles were established. The multi-layer detachment and wedge-shaped stacked structures create complex hydrocarbon migration paths in the Southern Junggar Basin with the reservoirs often having different gas-water relationships, and the oil and gas exploration potential being extremely hard to be deciphered. As mentioned above, the connectivity of the “vertically laminated” structures with source kitchen and late preservation condition are critical to the hydrocarbon accumulation in the area. Due to the “laterally migrated and vertically stacked” characteristics of the hydrocarbons, the differences in the connectivity of each laminated structure to the source kitchen resulted in different exploration potential. Therefore, the current oil and gas exploration in the Southern Junggar Basin should change exploration strategy by no longer taking the overall anticline structures as exploration objectives, but treating them different according to the different laminated structures even within the same structural belt. Analyzed from oil and gas charging condition and its matching relations, the deep assemblages (such as Assemblage II and below) have better communication condition with source kitchen and preservation condition, and the deep laminated structures in Assemblage III should be the focus of current exploration target.