Research On The Sedimentary Facies Of The Second Member Of Guantao Formation?Ng₂?in Lin 2 Fault Block Of Linpan Oilfield

The Lin 2 block,located in the west of the central uplift belt within the Huimin sag of the Jiyang depression,is a nose-like structural reservoir bounded by a west-east trending and southward-plunging normal fault.This faulted block is recognized as one of the main oil-bearing faulted blocks in the Dalujia area of Linpan Oilfield and has already entered the later phase featuring“three overproof”:high water yield,high recovery degree,and high yield rate.But some fundamental geological problems remain unresolved,including inconsistent division and comparison of thin layers,debate in the understanding of sedimentary micro-facies,lack of knowledge of the law of sand body development,and unclear knowledge of heterogeneity of reservoirs.In order to further recognize the distribution law of residual oil and improve the development effect,detailed research should be conducted on these fundamental geological problems.This paper was directed by theories such as sequence stratigraphy,sedimentology,and subsurface geology of oil and gas fields,and fully utilized previous achievements and project data.Various methods were applied to conduct fine division and comparison of layers in the research area:controlling by marker layers,comparison of elevation,comparison of superimposedsand bodies,and comparisonof facies-changing sand bodies.The Ng₂ accordingly is divided into four layers.Besides,modeling data were adopted to analyze and summarize the thickness of each layer.With the fine stratigraphic framework established,in-depth analysis of sedimentary micro-facies was conducted on the basis of lithological features,logging and well log data,and regional geological data.It suggests that braided fluvial facies mainly of riverbed subfacies and flood plain subfacies developed in the Ng₂.Four micro-facies were recognized within:channel bars,channel filling,and flood plains,and alluvial flat.The features of the distribution of above micro-facies in the profile and plane were summarized.The rock core data and second logging interpretation results were adopted to research the characteristics of reservoirs and heterogeneity.Through calculation of parameters including the development scale and occurrence of sand bodies,the development features of sand bodies were clarified.Sand bodies in reservoirs develop in patterns of cut-stacking,lapping,and isolating.On the basis of the diagram of well-tie comparison of sand bodies and the diagram of planar sand body distribution,the development law of sand bodies in profile and plane was figured out.Sand bodies exist mostly as micro-facies of channel bars and filling,secondly as flood plains,which show as connected patches or strips.The research of intra-layer heterogeneity,interlayer heterogeneity,and planar heterogeneity and others suggests that the degree of heterogeneity of reservoirs in the Ng₂ is fairly uniform and appraised as medium;difference of permeability between layers is minor and heterogeneity weak.Based on the sedimentary micro-facies classified,reservoir physical property,modeling achievements,etc.,favorable reservoir zones within the No.0-2 layers of the Ng₂ were delineated.The semi-quantitative analysis of parameters including encounter rate,thickness of sand layers,physical properties,effective thickness of sand bodies indicates that the Ng₂ No.1 layer was rated the highest quality and the I class reservoir,the Ng₂ No.2 layer is rated as the II class,and the Ng₂ No.0 layer as the III class.