| In foreland basins of Central and West China, the exploration shows there is rich in hydrocarbon and has a lower rate of proven resources. The study of new method and the application of new technology, which are important to speed up the exploration of the complex tectonic belt in the foreland thrust belt. This paper discusses the seismic modeling for structural analysis of the foreland thrust belt in west Sichuan. Based on study of the Dayuanbao area, the hydrocarbon exploration methods is mapping source rocks and researching the hydrocarbon preservation conditions to determine favorable areas for oil and gas exploration, mapping the distribution of the high-quality reservoirs assemblage to determine the gas distribution layer, studying the trap development characteristics to determine the location of the gas reservoirs. At the same time, this paper focuses on the seismic modeling using3D seismic image and seismic attributes, and applied geophysical methods combination with the geological means for exploration of Dayuanbao area.Dayuanbao area is in the front of the Longmen mountains thrust belt, western Sichuan foreland basin. The main structure controlled by Tongjichang fault, Guankou fault and Penxian fault. Guankou fault is the extending southward of the Anxian-Dujiangyan fault, it is a northwestward plow fault, and within a thrust wedge tectonics at the fault terminal. Tongjichang fault is formed late and thrust to the ground. Based on the seismic images, the Dayuanbao structure is a positive structure between Tongjichang fault and Guankou fault.Seismic modeling relies on formed the surface geological sections, Seismic interpretation, geometry modeling and kinematics analysis of the tectonic. Seismic interpretation from3D seismic image volume, which can be processed without changing the original data, is more convenient. The volume of3D seismic image enables to enhancing process and then interprets directly. Based on PDE, eigenvalue analysis and edge detection, the faults of3D seismic image volume were interpreted with the computations accelerate with GPU (Graphic Process Unit) implementation. The practical application result shows that this method can effectively improve the objectivity and efficiency of the interpretation of3D seismic data.Neural Network Classification of multi-seismic attributes used to faults detection, which can help quick structure interpretation. Then, multiple detachment structure of the Dayuanbao was ascertained by geological and geophysical files. The main strata of Dayuanbao structure are the Permian and the Triassic. According to the research of the deformation and fracture of the Xujiahe formation from Tongjichang to Guankou, the outcrops of Xujiahe formation at Siwenchang and Baishuihe, it is belong to the hanging side of thrust sheet, and thrust to exposure in late Triassic period, then covered by Baitianba formation. It shows that the Dayuanbao structure is a fault-bend fold of Permian system in he early stage of Himalayan, which analyzed by the reconstruction form of the back limb of Dayuanbao and the spread pattern of the ground structure in Penxian area.Through the analysis of hydrocarbon source condition, the main hydrocarbon source of the marine strata in Sichuan basin, which are lower Cambrian, lower Silurian, lower Permian and upper Permian. The hydrocarbon source of the Doushantuo and upper Permian is less contribute to the front of Longmen mountains, moreover, the lower Silurian hydrocarbon source is deletion in west Sichuan. So, the main hydrocarbon source contribution to the front of the Longmen mountains should be lower Cambrian.The study of fluid characteristics shows that the fluid is gradually lateral migration from the combination of basin and mountain to the foreland basin. The lateral migration of the fluid is not a large-scale trend. There is better preservation conditions below the thrust belt compared with the thrust microlithon above the sliding plane. In foreland uplift area, there have been hydrocarbon gathering and accumulation, and has formed paleo-reservoir and paleo-gas-reservoir. At the same time, there were good preservation conditions. In the process of transforming paleo-reservoir into paleo-gas-reservoir between Indochina to Yanshanian, some pyrolysis gas dissolved into water and then formed water-soluble gas. The tectonic uplift occurred from late Yanshanian to Himalayan, which lead to the damage, adjustment and re-accumulation of the paleo-gas-reservoir. According to the reservoir characteristics of Middle Triassic sedimentary evolution, and the discovery of calcareous sponge in leikoupo formations, which indicate the T213is the target layer. By geophysical methods analysis of the gypsum in Leikoupo, it can be considered that the preservation conditions are destroyed which is the reason of failing to form reservoir. Then further study shows the prospective exploration area at the buried structure below the Guankou fault. |
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