Analysis On Characteristic Of Tectonic Inversion In The End Of Dongying Stage In Jiyang Depression

Based on comprehensive analysis and interpretation of various datas such as seismic, well-logging, mud logging, cores and previous research, this paper established method for distinguishing inversion structures in extension rift basin, comprehensive distinguished the inversion structures at the end of Dongying stage in Jiyang depression and had make sure the distribution and geometric characteristic of inversion structures. Then further analysed their kinematic process, and quantitative expressed inversion intensity of basin, faults, and concrete inversion structure by the methods of balance section and extensional rate analysis, strata erosion amount, fault activity analysis, inversion intensity calculation and so on. On this base, combined evolution rule of regular geodynamic background with selectivity analysis of tectonic inversion, this paper made the genetic mechanism of tectonic inversion at the end of Dongying stage in Jiyang depression cleared, discussed the relation between tectonic inversion and hydrocarbon accumulation, the established the oil and gas accumulation model of inversion structures.Tectonic inversion at the end of Dongying stage in Jiyang depression showed as lateral compression, vertical uplift of basin, fault conversion from normal to reverse, and the forming of positive inversion structural styles: the basin were mainly compressed in EW and NE laterally; and the basin were mainly uplift and erosion in vertical, the erosion of salient were thicker than sag. However, concrete positive inversion structure distribution was localized, which were just existed in the east segment of Chennan fault and the middle segment of Gaoqing-Pingnan fault. And the structural styles can be divided as two kinds such as single fault-extension and cut-off fault-extension. The east segment of Chennan fault is single fault-extension and cut-off fault-extension, the middle segment of Gaoqing-Pingnan fault is single fault-extension, inversion intensity of the east segment of Chennan fault is bigger than he middle segment of Gaoqing-Pingnan fault; in addition, Chengnan fault is defined as"suspected"inversion structure because of various sand-conglomerate fan.Deep lithosphere rebound is the main reason of basin inversion; the strong collision of Indian plate and Eurasian plate, West of the Pacific plate subduction in NWW and dextral pressure twisting movement of Tanlu fault zone made Jiyang depression been squeezed in NEE-SWW at the end of Dongying stage. Adding the differences of pre-existing fault dip, shale content of sag at the hangling wall, abnormal high pressure, and pre-existing structures were selective inversion at the end of Dongying stage. Tectonic inversion at the end of Dongying stage in Jiyang depression has some control and influence to hydrocarbon accumulation. Structural inversion delayed secondary hydrocarbon of deep hydrocarbon source rock, affected primary migration dynamic of source rock, controlled the channel and direction of hydrocarbon migration. By the way, development of positive inversion anticline has some influences in improving reservoir property and ability, expanding the trap range and increasing oil and gas reserves finally.