Research Of The Structural Characteristic Of Shigang Fault Zone Of Jinhu Sag

Based on the theories of sedimentology, structural geology and petroleum geology, combining previous research, using lots of core hole information, seismic data, well-logging data and methods combining qualitative analysis and quantitative calculation, geological and geophysical, fault system, structural evolution, fault active strength and genesis mechanism of Shigang fault system, Jinhu sag are systematically researched.Located in the mid north part of west slope of Jinhu sag, Shigang fracture zone goes northeast trended. According to the seismic interpretation result, the tectonic style presents as segmentation in the plane. It is broom-like in the south, braided and echelon styles in the center and comb-like in the north. It presents as layered vertically which is echelon-like in Funing Group and minus flower-like in Dainan and Sanduo Group.Analysis of fault throw and fault growth index shows that fault movement strength of Dainan and Sanduo period is stronger than that of Funing period. From Dainan period to Sanduo period, strongly active fault extends from the west to the east of the minus flower structure. While the strongly active fault at Dainan and Sanduo period extends from south to north.The tectonic evolution profile shows that paleogene Shigang fault system turns complex. At Funing period, fault in the sides develops in the process of main fault’s activity. At Dainan and Sanduo period, the minus flower structure forms, and fault throw increase rapidly. It is mainly extensional activity in early stage while strike-slip activity in late stage.On the base of seismic interpretation, and according to the analysis of tectonic evolution profile, fault growth index, paleo-throw, the tectonic evolution of Shigang fault system can be divided into 3 periods. The 3 periods are active stage of strike-slip extensional main fault at Funing period, developmental stage of strongly extensional strike-slip minus flower structure at Dainan and Sanduo period and stable subsidence stage at Quaternary.Fault Shigang remains active at Funing period. Numerical simulation results of tectonic stress field show that high-value region of main tensile stress and difference stress distributes in the sides of Fault Shigang where the secondary fault develops. Shigang region, Qiaohekou region and the thrown side of north part of Fault Shigang is the positive-value region of plain shear stress, where east-west trended fault develops. The value of south-north trended section shear stress in the thrown side of Fault Shigang is mainly positive, where the fault of north-tendency develops.Fault Shigang remains active in deep area at Dainan and Sanduo period. According to numerical simulation results of tectonic stress field, high value region of main tensile stress distributes in the sides of Fault Shigang where the secondary fault develops. The south and north part of Fault Shigang is the positive-value region of plain shear stress, where east-west trended fault develops. While the central part of Fault Shigang is the negative-value region of plain shear stress, where northeast trended fault develops. The value of south-north trended section shear stress in the walls of Fault Shigang is mainly positive, where north-tendency fault develops.The results of simulation of fracture parameter show that the fracture is formed by paleo-stress field at Funing period, and then being reformed by current stress field. Fractures mainly develop near Fault Shigang, which are north-northwest trended as a whole. The high-value regions of fracture density, aperture, porosity and permeability distribute near the fault in Shigang region.