Mapping of oil-source faults in reservoir–cap rock combinations without a source rock

Oil and gas exploration near faults in shallow strata is investigated in this study based on an analysis of oil-source faults in reservoir–cap rock combinations without a source rock. The oil-source faults were mapped by superimposition of the distribution area of oil-source faults and the leakage area of cap rocks. This method is applied to the mapping of oil-source faults for two sets of reservoir–cap rock combinations without a source rock in the Banqiao area of the Qikou Sag in the Bohai Bay Basin, eastern China. Combination B is formed by a mudstone cap rock of the middle sub-member of the 1st member of the Shahejie Formation (E3s1M) with its underlying reservoir, while Combination C is formed by a mudstone cap rock of the 2nd member of the Dongying Formation (E3d2) with its underlying reservoir. The results show that the oil-source faults of Combination B are relatively better developed and mainly occur in the northeast and southeast, while those of Combination C are not as well developed and are only distributed at the southeastern edge of the study area with a small proportion in the north. These results are consistent with the fact that oil and gas are mainly distributed near oil-source faults, proving the method proposed is workable in determining the oil-source faults in reservoir–cap rock combinations without a source rock.