QUANTITATIVE EVALUATION OF “PALEOHIGH-FAULT” JOINT CONTROL OVER NEOGENE HYDROCARBON ACCUMULATIONS IN THE WEST SUBSAG OF BOZHONG DEPRESSION

In order to reveal the differential enrichment mechanism of Neogene hydrocarbon in the CFD12 area of the west subsag of Bozhong Depression, the control effect of paleohigh and faults on hydrocarbon accumulation is deeply studied. It is concluded that paleohigh determines the location of hydrocarbon accumulation; the effective faulted caprock thickness of Dongying Formation affects the hydrocarbon enrichment horizon; and the fault activity rate during the accumulation period controls the degree of hydrocarbon enrichment. The fuzzy mathematical method is used in this paper to quantitatively evaluate the controlling effect of paleohigh and fault on Neogene hydrocarbon accumulation. It shows that when the comprehensive accumulation index Y≤0.3, the proved reserves abundance is less than 200×10⁴ t·km⁻², indicating a low hydrocarbon abundance area; when 0.3＜Y＜0.8, the proven reserves abundance is (200～350)×10⁴ t·km⁻², indicating a medium enrichment area of hydrocarbon; when Y≥0.8, the proved reserves abundance exceeds 350×10⁴ t·km⁻², it is a hydrocarbon enrichment area. The quantitative evaluation method is applied to BZ 8-A structure which has a similar structural background to the CFD12 area, and is consistent with the actual drilling results. It may have more application prospect in similar areas of Bohai Sea.