Structural inheritance and its control on overpressure preservation in mature sedimentary basins (Dongying depression, Bohai Bay Basin, China)

Abstract

Overpressure in sedimentary basins has practical commercial importance for petroleum exploration as the steady maintenance of pore-pressure in reservoirs is important for CO2 sequestration. Traps associated with faults comprise >30% of hydrocarbon discoveries in the Dongying depression, Bohai Bay Basin. However, the way structural inheritance, together with fault reactivation and its development, influence pore-pressure development and overpressure preservation remain poorly understood. This research uses high-resolution 3D seismic data combined with well-log data to investigate the structural evolution in the Lijin and Boxing sags in the Dongying depression and elucidate the influence of structural inheritance on overpressure development. The interpreted data reveal that: 1) five fault families in the Lijin Sag influence overpressure development, 2) three phases of faulting occurred in the Boxing Sag, with fault reactivation predominating in the early Eocene and late Oligocene; and 3) pressure coefficients (Pc) in Eocene strata vary from 0.90 to 1.96 in the Lijin and Boxing sags. In the Boxing Sag, Pc values vary from 0.91 to 1.54 in the Eocene strata, with 99% of overpressure coefficients below 1.50. In comparison, pressure coefficients in the Lijin Sag are significantly higher than in the Boxing Sag, with Pc values varying from 0.9 to 1.96, and 30% of the Pc values are over 1.50. This study concludes that inherited structures significantly control the development of overpressure in sedimentary basins. Systematic fault reactivation often leads to fluid leakage, which has a negative influence on overpressure preservation. In basins with border faults controlling their evolution, high-magnitude overpressure tends to be generated and maintained, favoring the formation of pressure compartments, conditions less ideal for carbon sequestration.