| The Chang 6 oil layer of the Upper Triassic Yanchang Formation serves as the major oil-bearing reservoir in the H Oilfield X block area is located in Zhenjing area of southwest Ordos Basin.The study area is currently in the middle-late period of the development stage,Reservoir enters high water cut stage,there are multiple sets of superimposed sand bodies in the longitudinal direction of the target interval,and the reservoir changes rapidly.However,there are still some shortcomings in the traditional division of strata,the understanding of sedimentary facies,the overlapping relationship between sand bodies,and the understanding of connectivity,which cannot meet the needs of improving production efficiency.The main oil-bearing 622 interval in the study area is subdivided into three units,the distribution of sedimentary microfacies and characteristics and connectivity of single sandbody in this interval are studied by drilling,logging,seismic and production performance data,which provides the basis for optimizing the development and deployment.The Indosinian movement caused differential denudation of the upper Triassic strata in the study area.The unknown understanding of the interface in the past led to the unclear division and correlation of the Yanchang Formation.The identification of unconformity surface and the establishment of isochronous stratigraphic framework in Yanchang Formation have been completed through seismic,logging,lithologic association and marker bed data.Clarify the extent of the Jurassic eroded valleys and the erosion of the stratum in the study area.The eroded valleys spread northeast-southwest,and the Fuxian Formation and Yan 10 oil layer are mainly deposited inside.The Triassic strata upon the Chang 4+5 oil layer is mainly eroded in the study area.The Chang 622 interval could be is divided into three single sand layer by isochronous stratigraphic division and correlation,The strata are gradually thickened from southwest to northeast.According to core observation,logging and other data,there are 622 sublayers in the study area,and the gravity flow sediments of the subaqueous fan are well developed,including sandy debris flow deposit,turbidite deposit and slump deposit,it changed the previous viewpoint that Chang 622 interval was delta front deposit in study area.Different types of gravity flow have different sedimentary characteristics and development mechanism.By establishing the sedimentary model of gravity flow subaqueous fan,there are four sedimentary microfacies in the margin and middle of the subaqueous fan,it includes lateral channel,branch channel,sheeted turbidites and inter channel.Branch waterways are mainly distributed in the study area,which is caused by sandy clastic flow deposition.The development law of gravity flow subaqueous fan in the study area is summarized from horizontal,vertical and plane,and its fan body is multi-stage progradation and sedimentation.According to the physical properties and oil test data of gravity flow reservoirs in the study area,the correlation among sedimentary facies types,reservoir quality and oil and gas enrichment is summarized.The braided channels and turbidite sheet of subaqueous fan gradually decrease in physical properties and oil and gas enrichment.Under the isochronous stratigraphic framework,the boundary of a single sandbody is determined according to the change trend of inter-track sedimentation,elevation difference,and sandbody thickness.The vertical stacking relationship of single sandbody in the study area includes isolated type,superimposed type and cut superimposed type;The lateral contact relationship includes lateral separation,cut and stack.There are some differences between the single sandbody of gravity flow and traction flow in the study area,The cutting of single sand bodies in gravity flow is not obvious,therefore,the single sandbody in the study area can be divided into 7 periods of composite single sandbody.Through the thickness map of each period of the sandbody on the plane,The distribution pattern of composite single sandbodies and the superimposed relationship between sandbodies in each stage are clarified.Through the oilfield production dynamic data,it shows that the single sand body characterization is reasonable,which can provide guidance for well pattern optimization and water injection development. |
