Sedimentary Facies Characteristics Of The Yingcheng Formation In The Longfengshan Area Of ??the Changling Fault Depression

With recent years' exploration of Longfengshan area in Changling fault depression,it is proved that the sand body with great continuity show favorable potential of oil&gas exploration.the confirmation of main source directions and sedimentary facies is very important in the first stage of exploration in Longfengshan sub-sag.Based on the data of cores,logging,seismic and thin-sections,this article analysised the distribution source,types of sedimentary facies and favorable sedimentary facies.The results are showed as follows:The distribution of source in Longfengshan sub-sag was confirmed through various evidences including assemblage type and Q-type cluster of heavy minerals,clastic composition,and sandstone-conglomerate content.The result shows that there are two main provenances of Yingcheng member,including southwest metamorphic rocks and southeast magmatic rocks.The mixed source district was formed because the southwest and southeast source stack together.The identification standard of different sedimentary micro-facies was established based on the signs of sedimentary facies in Longfengshan area.Braided river deltas is developed along the direction of minor axis of southwest gentle slope zone,and fan delta is developed along the major axis of southeast steep slope zone in half-graben rift lake basin.The sedimentary features of fan deltas are characterized with the gravity current and tractive current sediments combined effection.The sediment composition maturity and structural maturity of fan deltas are lower than that of braided river deltas,and its seismic reflection characters are chaotic seismic facie sand forest seismic facies.The sedimentary characters of braided river deltas reflect the tractive current sediment effection,and lack gravity current sedimentary sand body.The sand body formed by braided river deltas flow into lake far away along gentle slope zone,and its seismic reflection characters is S-shaped foreset.At the base of the research of individual well,correlation profiles and plane sedimentary facies,the evolution of sedimentary was determined in Longfengshan area.The basin is in the expansionary phase in the Ying IV sub-member,and fan deltas have large scale distribute.In this sedimentary background,the delta subaqueous sand scale is large in lake basin because the fan-delta subaqueous and braided river delta subaqueous stacked on each other.The basin was shrinking gradually as well as fan delta in the late Ying IV period.At this moment,the barided river delta developed with great scale,and the barided river delta subaerial distribute widely along the fault F4,the subaqueous distribute as a strip.At the base of sedimentary facies,we utilize some reservoir characterization techniques such as physical properties testing,computed tomography(CT),constant-rate mercury penetration and casting thin sections to determine the distribution and formation mechanism of favorable sedimentary facies.The gravel bearing fine sandstones were cemented by laumontite in the early diagentic affected by alkaline water of lake,and form massive laumontite dissolved pore in the delta subaqueous.The delta subaqueous is the favorable sedimentary facies due to the charging of oil&gas in Longfengshan area.