The Structural Features In The Middle Of Longmen Mountain And The Discussion On Exploration Prospect

Longmen Mountains thrust belts is located in the west side of Sichuan basin, the boundary of Yangzi platform and Songpan-Ganzi area. It is a huge structure belt extending from NE-SW, whose structure is complicated and changeful. According to the tectonic geometry ,kinematics and so on, the present paper has studied the structure combination and distribution in the middle segment of Longmen Mountains, discussed the formation mechanism and evolution of Longmen Mountain thrust belt and Sichuan foreland basin, combining with the field investigations and seismic interpretation.The four large-scale faults control the distribution and the tectonic zoning characteristics of Longmen Mountains thrust belt. From west to east, the studying area can be divided the Songpan-Ganzi fold bel(tI),the Longmen intracontinent composite orogen(II),the Sichuan foreland basin(III). From the orogen belt to Sichuan basin, the intensity of tectonic deformation gradually decreased. The structural deformation appears in different levels vertically.The main structural types in the area consist of imbricated thrust system, klippen, duplex, pop-up, triangle zone, fault-propagation fault-bend and gentle fold and so on.The critical tectonic movements in the Longmen Mountains thrust belts are early indo-Chinese orogeny, Anxian orogeny, late indo-Chinese orogeny, Yanshan orogeny and Himalayan orogeny. The Indo-china orogeny and Himalayan orogeny are the key tectonic movements on the formation of Sichuan foreland basin. After the Anxian orogeny, the regional stress field of the Longmen Mountains changed hugely. The stress field changed from northeast-southwest to northwest-southeast, formatting Longmen Mountains thrust belts. The thrust activities further developped, uplifted and finally formed the current complex structure pattern.The tectonic styles of Longmen Mountains are very complex. The multiphase tectonic activities determined the distribution of hydrocarbon and the characteristics of traps. Early accumulation and later seal are the basic characters of gas reservoir formation in the front of Longmen Mountains. The tectonic movement in the Himalayan orogeny impacted the storage conditions, the final shape of the structural style, which has a decisive role in the trap formation. Through the study of fault sealing, combination of Longshen well 1 data and the fluid chemical information, it can be achived that the faults on the nappe sliding surface developed considerably and the formation suffered breakage seriously, resulting in bad conditions for oil and gas accumulation. However, the tectonic movement effect is weak in the native system, and the coverage of sliding surface and gypsum protected the native system, so the native system maybe have good conditions for hydrocarbon accumulation.