Research paperDifferential compaction faults and their implications for fluid expulsion in the northern Bozhong Subbasin, Bohai Bay Basin, China

- The differential compaction faults (DCFs) developed along a lithologic interface.
- Tectonic faults, basin slope and basement topography control the strike of DCFs.
- DCFs developed in a late period when source rocks enter the oil-generating stage.
- DCFs play an important role of fluid expulsion and hydrocarbon accumulation.

A series of differential compaction faults was identified in the northern Bozhong Subbasin, Bohai Bay Basin, China, by using 3D seismic, well log, and lithology data. The differential compaction faults display two obvious characteristics. First, they develop along a lithologic boundary which separates thick sandstone from underlying mudstones. Facies and thickness change, such as an abrupt lithologic change between sandstone and mudstone, a lateral thickness change of overlying sandstone, are the basic controlling factors of these differential compaction faults. Second, they have a definite strike direction. According to the fault strike, the differential compaction faults can be divided into three groups: Group (a) have an approximate orthogonal strike with the tectonic faults, Group (b) display a similar strike with the slope, and Group (c) show radial strikes on the circular basement uplift. Tectonic faults influence the planform patterns of differential compaction faults in their near vicinity and induce these faults displaying an approximate orthogonal intersection with the late-period through-going faults (Group a). Basin slope promote the formation of differential compaction faults by downslope gravity sliding and cause faults parallel to the strike of slope (Group b). Circular basement topography generates isotropic stress and leads the differential compaction faults above the basement dominated by radial strikes (Group c). Production and geochemistry data is an evidence of differential compaction faults developed in a late period when the strata reach a certain burial depth that the source rocks enter the oil-generating window. The presence of thermogenic fluid within shallow reservoirs represents as evidence of hydrocarbon drained and migrated through the differential compaction faults. The differential compaction faults could serve as significant conduits for fluid expulsion and hydrocarbon accumulation in the Bohai Bay Basin, China.