Characteristics and Evolution of a Strike-Slip Fault Zone and its Function on the Control of Petroleum Accumulation: A Case Study from the Tanlu Fault Zone within the Bohai Bay Basin, China
Teng, Changyu; Zou, Huayao; Hao, Fang
The Tanlu fault, a major NNE-trending strike-slip fault, runs through the east of the Bohai Bay Basin which is a petroliferous Cenozoic basin in east China. Since the Oligocene, it shows a dextral strike-slip movement. The characteristics vary significantly with depth and locations along the strike. Additionally, it plays a vital role in the control of petroleum accumulation. Based on the interpretation for 3-D seismic data and the analysis on variance cubes, the fault patterns at different depth and locations are displayed and compared, and the strike-slip fault zone evolution models are established in terms of the geometries of damage zones observed on the Tanlu fault zone. Moreover, the Allan maps are drawn up to demonstrate whether a fault is sealed or not. This study points out the damage zones of the Tanlu strike-slip fault can be grouped into 3 types according to the master fault patterns. (1) Oblique-slip Damage Zone. It is produced by the oblique-slip movement of the pre-existing listric normal boundary fault. Extension fractures firstly develop at the down-dip tip with thicker layers, whereas Riedel (R) shears appear at the up-dip tip with thinner layers. Toward the shallower layers, the extension and the R fractures tend to link together with their angles increased. Conjugate Riedel (R') shears produced by the extension fractures propagating upwards are usually the first to appear near the top of the layers. (2) Typical Strike-slip Damage Zone. It is possible for R', R or extension fractures to develop as en-echelon above the master fault, which mainly depend on the thickness of the layers. As the depth increases, the angles of the fractures are decreased gradually, and then smaller angular R shears breach the oversteps and link the incipient fractures together, giving rise to a throughgoing fault zone. (3) Linkage Damage Zone. It is produced at the oversteps of right-stepping faults, and en-echelon extension fractures firstly appear. As the depth increases, the fractures are linked by P shears, and all of them curve to make smaller angels to the master fault, forming a throughgoing fault zone at depth. The extension fractures easily cause the juxtaposition of formations with different lithology and shale smearing, so they benefit petroleum accumulation. However, the R', R, P shears and the strike-slip segments of an extension fault are difficult to produce the juxtaposition or shale smearing, neither for petroleum accumulation.
AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013