Sedimentary Characteristics and Model of Gravity Flows in Yan 18 Area of the Steep Slope in Dongying Sag of Jiyang Depression

Sand genesis,scale,sedimentary facies composition and development rules of sedimentary rocks from Yan 18 area in the steep slope of northern Dongying sag of Jiyang depression were studied by using rich geological and 3D seismic data,according to the characteristics of the steep slope of rift lacustrine basin with extensive tectonic activity,small-scale deposition and the highly heterogeneity of reservoir.Five kinds of gravity flow deposits were identified,i.e.liquefied flow,turbidity current,particle flow,muddy debris flow and sandy debris flow.Sandy debris flow deposit,turbidite,liquefied flow and grain flow declined in drilling degree,with 2.9,2.6,0.75,0.3 drilled layers through every 10m respectively.The statistical results prove that the single sedimentary thickness of muddy debris flow was the largest one,sandy debris flow the second,turbidite the less,and their maximum thickness were of 4.0m,3.5m,1.4m and average thickness of 1.2m,0.45m and 0.2m respectively.Study shows that sandy debris flow deposit was the most favorable sand type of all gravity flow deposits in the steep slope,and then was the thick turbidite.Additionally,four types of gravity flow-related sedimentary facies,i.e.,fan delta,nearshore subaqueous fan,slump sublacustrine fan and flood sublacustrine fan,have been recognized.Three stages of sedimentary environment evolution were discussed from the bottom up,the shallow water fan delta deposits,the deep-water nearshore subaqueous fan-flood sublacustrine fan-slump sublacustrine fan deposits,and the deep water nearshore subaqueous fan-slump turbidite fan deposits.Among them,the mid-fan subfacies of the flood sublacustrine fan and nearshore subaqueous fan were the most favorable subfacies for hydrocarbon accumulation,followed by the slump sublacustrine fan.