The pressure systems and dynamic mechanisms for oil and gas accumulation in the Boxing region,Shandong

The abnormal high pressures appear in the oil and gas pools from the third and fourth members of the Shahejie Formation in the Boxing region,Shandong.In the light of the distribution of stratigraphic pressures in a single well,section and plan with the aid of the acoustic logs for mudstone,the abnormal high-pressure zones in individual wells are delineated at the depth of about 2100-2500 m,horizontally related to the occurrence of mudstone in the third member of the Shahejie Formation.The residual fluid pressures are zoned,and constrained by tectonic setting,mudstone from the third member of the Shahejie Formation and faults.The high residual fluid pressure values occur in the depressions.The residual fluid pressure gradients are higher in structurally steep slope zones,and lower in the ramp zones.The oil and gas are often accumulated in the relatively low-pressure areas and normal pressure areas within the abnormal systems.Two types of dynamic mechanisms for oil and gas accumulation have been distinguished for the Boxing region: authigenic enclosed type and allothigenic open type.