Comparative Study On The Main Controlling Factors Of Reservoir Forming Within Qinan And Qibei Slopes In Dagang Oilfield

Qinan and Qibei are two adjacent gentle slopes developed in the Qikou sag of Huanghua depression,but the oil and gas exploration situation of Qibei is far better than that of Qinan.As so it is necessary to strengthen the study on the theory of oil and gas accumulation in these slopes and deepen the geological understanding.Based on seismic,logging and testing data,this paper describes and compares proven oil and gas distribution rule and relevant geological elements,then explores the main controlling factors and pattern of reservoir forming within these slopes.The conclusions are as follows:(1)The commonality of oil and gas distribution between slopes are reflected in:(1)The number of proved oil reservoirs is more than that of gas;(2)Structural reservoirs are the most abundant type.The differences are as follows:(1)The proved oil and gas reserves of Qinan slope are much smaller than that of Qibei;(2)Medium slope and the short axis of Qibei,high slope of Qinan contain the most proved reservoirs;(3)Hydrocarbon accumulation in Qinan slope is relatively deep,while that in Qibei slope is relatively shallow;(4)Qibei slope contains more subtle reservoirs.(2)The differences between Qinan and Qibei in oil and gas accumulation elements are mainly reflected in:(1)The hydrocarbon generation center of major source rock is located in the low slope of Qibei,also outside Qinan slope;(2)There are mainly long-axis provenance,forming a single-direction sand body in Qinan.There are long-axis and short-axis provenance,forming sand bodies in two directions in Qibei;(3)The long axis of Qinan and the short axis of Qibei are larger in seal thickness;(4)The EW-trending secondary faults developed in the high slope of Qinan,and all the secondary faults in Qibei are NE-trending;(5)Only the north?south boundary of Qibei and the north boundary of Qinan slope develop secondary faults with long extension;(6)Sand body connectivity are better in the middle part of Qinan and the short axis of Qibei;(7)Small structural ridges developed from Qinan subsag,large ones developed nearly parallel along the north and south boundary of the Qibei slope.(3)Structural morphology controls the type of reservoir.Source rock and hydrocarbon expulsion center distribution influence oil and gas enrichment.Transport system control plane and vertical distribution of oil and gas reservoirs.Oil and gas accumulation in Qinan is controlled by advantageous transport system,while that in Qibei is controlled by source-reservoir distance,advantageous transport system and the flexural structure.Based on the tectonic background,source rocks and transport elements,the long axis of Qinan is characterized by "gentle slope-unilateral fault-ridge dominance-fault-controlled" forming pattern,the long axis of Qibei is characterized by "gentle slope-bilateral fault-ridge dominance-source control" pattern,and the short axis is characterized by "near-source-stair-step transport-fault-controlled" pattern.