Revitalization of a mature oil-bearing basin by a paradigm shift in the exploration concept. A case history of Bohai Bay, Offshore China

The Bozhong Depression in Bohai Bay was previously ranked as an unfavorable exploration region due to concerns about reservoir, trapping integrity and top seal risks.In the mid 1900s, a few explorationists began to view the petroleum accumulation conditions more positively. They argued that rapid Neogene subsidence could have generated a new suite of source potential and that recent continued fault movements may have provided the needed conduits for upward hydrocarbon migration. They predicted the existence of lacustrine facies that could supply the needed lateral and top seals for the intensively faulted traps. These radical thoughts were gradually formulated into a new concept for the Neogene targets. This paradigm shift in exploration concepts has, since 1995, led to the discovery of nine (9) major oil fields with a combined in-place reserves more than double those discovered in the previous thirty (30) years. Some of these Neogene reservoirs appear to be at a dynamic balance between hydrocarbon escape and charge. It is speculated that the required driving energy for the charge may have come from earthquake activities.