| Globally,the deepwater gravity flow system is regarded as an important hydrocarbon reservoir,both in marine basins and inland basins.Gravity flow sand bodies contain a large amount of hydrocarbon resources and are an important target for hydrocarbon exploration.The paper is based on core data,seismic data,logging data,etc.,combined with previous research on the Longdong Area Yanchang Formation,the Longdong area stratigraphy,petrography,sedimentary phases,sand bodies,etc.The paper breaks the traditional "sign layer constraint,equal thickness division" stratigraphic division method,the Longdong Area extensional formation in the middle and upper stratigraphic redivision,on the basis of this study area lithofacies,lithofacies associations,sedimentary micro-phase type,on the basis of sand body prediction,for the study area oil and gas exploration and development to provide guidance.In total,the paper has achieved the following conclusions and understanding:(1)Longdong Area in the latest acquisition of three-dimensional seismic data profiles found in the typical pre-consolidation structure,in the pre-consolidation structure on the basis of research,using the "marker layer control,unconformity interface natural tracing,three-dimensional spatial closure" method,the establishment of isochronous stratigraphic framework.On this basis,the upper and middle strata in the study area were re-divided into 5 strata from P1 to P5 from the bottom up,and 47 skeleton sections were established in the work area,10 sections in the NE direction and 6 sections in the SE direction were selected for key studies.(2)The petrographic phases in the study area are classified into nine types of lithofacies,such as massive laminated fine sandstone phase,interlaminated fine sandstone phase,parallel laminated fine sandstone phase,Bauma sequence pink(fine)sandstone phase,dark mud(shale)phase,tuff phase,etc.,and seven types of lithofacies associations,such as massive laminated fine sandstone phase-dark mud(shale)phase,massive laminated fine sandstone phase-Bauma sequence pink(fine)sandstone phase-dark mud(shale)phase,Bauma sequence pink(fine)sandstone phase-dark mud(shale)phase,etc.(fine)sandstone phase-dark mud(shale)phase,Bauma sequence pink(fine)sandstone phase-dark mud(shale)phase and other seven types of petrographic combination.(3)Using the core data,logging data and seismic data of the study area,the sedimentary phases of the study area were studied,and the study area was divided into two major sedimentary systems: deltaic sedimentation and lacustrine sedimentation,which can be subdivided into four phases: braided river deltaic sedimentation phase,curved river deltaic sedimentation phase,gravity flow sedimentation phase and lacustrine phase,and further divided into braided river deltaic foreland phase,curved river delta foreland phase,and 7 sub-phases and 13micro-phases,such as semi-deep lake-deep lake,have been established and analyzed for sedimentary evolution characteristics.(4)During the deposition period from P1 to P4,the sediments gradually advance to the center of the lake basin from the source direction,and the deltaic sediments and gravity flow sediments continuously fill up the center of the lake basin,and the area of the lake basin continuously decreases,and the deltaic sediments are widely developed in the study area during the deposition period of P5.(5)On the basis of the study of high-precision stratigraphic framework,sedimentary micro-phase type and sedimentary system distribution characteristics,the sand body of the target section of the Yanchang Formation was predicted by combining seismic data.The prediction results show that the sand bodies are mainly distributed in the submerged diversion channels in the gently sloping zone(top accumulation section)and the gravity flow-forming sand bodies in the middle and lower part of the slope-folded zone(front accumulation section)to the depressional zone(bottom accumulation section). |
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