Configuration analysis and plane distribution characteristics of single sand body in Chang 6 reservoir formation of Heishanliang area,Ansai oilfield
Heishanliang block of Ansai oilfield is located in Ansai area,Yan'an City.The Triassic Yanchang Chang 6 oil formation is its main oil producing layer.At present,the area has entered the stage of water injection development,but there is a lack of clear understanding of the distribution,heterogeneity and stacking patterns of sand bodies,leading to problems such as imbalanced water injection efficiency and overall poor water drive effect during the development process.Therefore,this study relies on rich logging data,core data,microscopic thin section data,and analysis test data to conduct a comprehensive study on fine stratigraphic characterization,sedimentary microfacies,sand body plane distribution and single sand body stacking law.The results show that during the Chang 6 period,the delta front subfacies were mainly developed in the Heishanliang area,with fine-grained feldspathic sandstone as the main lithology,moderate to good sorting and roundness.Underwater distributary channels and inter distributary bay microfacies were more common,and the development of mouth bar microfacies was less;the underwater distributary channel is the dominant facies,and the sandstone is widely distributed and thick,extending along the river channel.The early formed estuary dam was damaged due to wave action and erosion of the distributary channel,and the estuary dam cannot be preserved completely,with only some traces.The types of sand bodies include underwater distributary channel sand and estuarine dam sand.The vertical stacking of single sand bodies can be divided into three types:isolated type,stacked type and shear stacked type;the lateral splicing styles can be divided into three types:isolated,docking and side cut.The sand bodies in the research area are distributed in a long strip shape along the northeast-southwest direction,due to frequent oscillation and bifurcation of the river channel,the sand bodies are significantly cut and stacked,and the connectivity of the sand bodies along the source direction is good.The sand bodies in the vertical source direction are separated by the bay mud between the distributaries,resulting in poor connectivity of the sand bodies.Based on this research result,a sedimentary model of the meandering river delta in the study area was established,providing geological basis for improving the injection production well network and adjusting the layered water injection development plan in the later stage of oil reservoirs.
Meandering river deltaSand body configurationSedimentary modelChang 6 reservoir formationHeishanliang areaAnsai oilfield
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