DISTRIBUTING CHARACTERISTICS OF FLUID PRESSURE IN THE ZHANHUA SUBBASIN, JIYANG DEPRESSION,BOHAI GULF BASIN, AND THEIR INFLUENCE ON OIL AND GAS ACCUMULATIONS

Six types of fluid pressure are distinguished on the basis of integrating measured data and theoretical calculation.Normal pressure is dominant in oil and gas accumulations in the Zhanhua subbasin,but high abnormal-pressure oil and gas accumulations exist in strata at depth.In a plan view,high abnormal pressure mainly occurs in areas of steep slopes or subbasin centers;whereas low abnormal pressure occurs on gentle slopes.In vertical sections,high abnormal pressure mainly occurs in the less compacted zone at depth;both high and low abnormal pressures may appear in the mixed compaction zone at moderate depth;and normal pressure predominates in the normal compaction zone at shallow depth.The target of petroleum exploration in the deep part of the Zhanhua subbasin should be relatively low potential areas in high potential areas or low potential areas near high potential areas,and one of the important problems lies in combining the distribution characteristics of fluid pressure with the potential distribution to look for hidden traps and favorable reservoirs.