Research On Characteristics Of Hydrocarbon Accumulation In Lixian Slope,Raoyang Sag

Located in the west of the Raoyang sag,Lixian slope has plenty of oil and gas resources and an exciting exploration potential.However,with the increasement of exploration degree,the discovery of remaining structural reservoirs becomes more and more difficult.In fact,most of the discovered reservoirs are mainly distributed in the midnorthern slope,and our studies about Paleogene reservoirs' characteristics and hydrocarbon accumulation mechanism are mainly focus on the northern slope.Whether the southern slope owns good conditions of oil accumulation and helps increasing potential production for Lixian slope is still unclear.Therefore,through comparative analysis of hydrocarbon distribution pattern and reservoir forming characteristics of southern,median,and northern Lixian slope,this study mainly analyzes the main controlling factor of oil-gas accumulation of each zone to provide theoretical basis for further oil-gas exploration in Lixian slope,Raoyang sag.Based on drilling,logging,seismic data and geochemical testing documents,combining the method of comprehensive geological researches,this thesis discusses the geological characteristics of Paleogene reservoirs,chemical characteristics of source rock and crude oil,oil-source correlation,reservoir anatomization and main controlling factors of hydrocarbon accumulation in Lixian slope.The research shows that there are three sets of source rocks contributing to the reservoirs of Lixian slope: the low mature source rock in lower sha 1 member,as the main source rock;the mature source rocks in sha 3 member and sha 4-kongdian formation.By oil-source correlation,this thesis considers that oil in the southern slope zone mainly comes from lower sha 1 member in Suning sub-sag and only a small part of oil comes from sha 3 member,Suning sub-sag.Oil in the median slope zone totally comes from lower sha 1 member both in Suning and Renxi sub-sag.Oil in the northern slope zone partly comes from lower sha 1 member in Renxi sub-sag,and some oil in the north of northern slope come from sha 4-kongdian formation in Dianbei sub-sag.By means of analyzing reservoir,reservoir-seal assemblage and passage system characteristics,summarizing the main controlling factors of hydrocarbon accumulation in each slope zone,it shows that the existence of a large number of antithetic sealing faults,short distance to multiple source sub-sag and thick regional caprock are the main controlling factors of oil-gas accumulation in northern slope;the overlapping sand on the limbs of nose structures,the existence of deep synthetic fault which acts as a bridge between reservoir and source rock;antithetic sealing faults controlling the accumulation of oil-gas in median slope;the perfect combination of nose structure and antithetic sealing faults,thick connected sand bodies and delta front subfacies depositional system in intraslope are the key controlling factors of hydrocarbon distribution in southern slope.