Genetic Mechanism And Oil-Gas Analysis Of High And Steep Structure In East Sichuan

The structures in east Sichuan, located in east Sichuan Basin, are composed of ejective folds. As they contrast sharply in landform and have steep dip, they have been named high and steep structure. The basement in east Sichuan is folded in which has several great faults. These faults have the same direction as the folds. The Huayingshan and Qiyaoshan faults become the boundary between ejective fold in east Sichuan and fornix in middle Sichuan, trough-like fold. At the same time they control the sedimentary growth of cover. The characters of cover are provided with tight anticline, open syncline and asymmetry of limbs. The surface faults are less and develop mainly in the cores of high and steep anticline, but the ventral stratum abounds with faults. The distortion of surface is clearly inconsistent with venter. Based on the studies of the basement structures, according to the viewpoint of inheritance and development, comprehensively using the new structural theories, such as extensional structures, inversion structures, fault related folds etc. and new results of inter-plate orogeny, the author systematically studied the evolutive mechanism of formation of high and steep structures and drew a conclusion that deformations of structures in east Sichuan basin had undergone a development which was the earlier great scale upwelling companied with giant sags , then the thrusting caused by gravity slip and ended with Jura-style folds due to the extrusion and sliding. The author also put forward a Post-Indian genetic-geologic-model and analyzed the oil and gas-bearing characters of different types of structures. Based on the stamps of source, reservoir and cap of this region, the paper discussed the migration, in mid-carboniferous Huanglong formation, Permian Changxing formation, Triassic Feixianguan formation and Jialingjiang formation, from source rock to trap while understanding the controls to reservoir of ancient upheavals, faults, unconformities as well as tectonics guided by mentioned model. As the sub-surface structures in east Sichuan basin gets more and more clear depending on field work and the understanding of former research, the author analyzed the tectonic evolution, ancient structural stress field, gas migration and reservoir characterization in east Sichuan basin combined with geophysics and bore data, illustrated the key role of tectonics for reservoir. As a result, the mid or large field have been doped out and the investigative area were classified into three levels. And meanwhile the biologic reef and oolite shoal of Permian and Triassic formation along with Kaijiang-Liangping trough should be given more concerns when exploring carboniferous formation, as it is an important successor to maintain the capacity and product.