Forming mechanism simulation of Ying 26 transfer zone in Dongxin area

Key words:  Dongxin area  Ying 26 transfer zone  formation mechanism  stress field numerical simulation  structural physical simulation  low-grade faults  Dongying sag

Abstract:

An tenso-torsional experimental apparatus with diapirism is designed for Ying 26 overlapping transfer zone formed during Shahejie Formation depositional stage in responding to the regional stress field in Dongxin area, Dongying sag. The aim is to simulate the formation mechanism and to reveal the law of distribution and development in the fracture system. Moist arentilla is chosen as the experimental material from the sand, clay and their mixture with different moisture. Experimentation process is filmed in detail and interpreted accurately. The results of the experiment show that:The Ying1 fault and Ying31 fault did not result from an early fault dislocated by lately transfer fault; instead they formed as two parallel faults before the deposition of Shahejie Formation under the effect of the extension in about NE10°. As pre-existing faults, the extensional displacement of the two faults induced the first shearing transform fault in the transfer zone. The fault strike of transform fault is oblique with the stretching direction with 50-degree angle. The higher the overlap ratio of the two faults, the more developed the transfer fault. Then dextral strike slipping formed a series of en-echelon faults and the dominant strike direction is in accord with the direction of shear stress field. At last, the diapirism complicated the fracture system in the late stage. Low-grade faults grew mostly on the cross, round and the crotch of faults, especially in small blocks closed or semi-closed by secondary faults due to large differences between minimum and maximum principal stress in this area. In addition, shear faults are oblique in the plane and strike-slip in different directions, forming tilted local blocks. As a result, the distribution of low-grade fault is more complex.