Characteristics Of Low Permeability Reservoir Of Beach-bar Sand Bodies And Distribution Of High Quality Reservoir Of Eocene Es4s In Southern Gentle Slope,Boxing Sag

Beach-bar sand bodies of Eocene Es4 s in southern gentle slope,Boxing sag,as an important type of lithologic reservoirs,has shown perfect prospects for exploration and development.With combination of drilling data,well-log data as well as associated analytical testing,by taking beach-bar sand bodies of Eocene Es4 s in southern gentle slope,Boxing sag as the main research object,sedimentary characteristics and diagenetic features of beach-bar reservoir are analyzed,reservoir characteristics and their differences are summarized systematically.The most effective controlling factors are clearly pointed out,and with comprehensive classification and evaluation,distribution patterns of effective reservoirs are established.Beach-bar sand bodies of Eocene Es4 s in southern gentle slope,Boxing sag are mainly composed of finestone,siltstone and pelitic siltstone,interbedded with gray-green mudstone.The compositional maturity is midding while structural maturity is on high side.Characteristics of sedimentary structures indicate the effect of wave and coastal current,as well as bioturbation.There develops parallel bedding,cross bedding,wave ripple,and boring.According to sedimentary characteristics as lithology,granularity and structure,sedimentary facies can be divided into eleven types and rock assemblage can be divided into eight types which are formed during sedimentary event.Diagenesis of low permeability reservoirs of Es4 s in beach-bar sand bodies is characterized by moderate-strong compaction,multistage of cementation and dissolution,lime-mud matrix recrystallization and complex metasomatism.The sequence of diagenesis is compaction/early carbonate cementation?feldspar dissolution/ quartz overgrowth/authigenic kaolinite ? early hydrocarbon charge ? late carbonate cementation ? carbonate-cementation dissolution/pyrite cementation.Even though in the similar diagenetic conditions,diagenesis and its sequence are also quite different as a result of differences in sedimentary composition and structure.Combining core observation with thin section analysis,eight types of sedimentary-diagenesis integrated facies in beach-bar reservoirs are established,and the quantitative logging recognition of sedimentary-diagenesis integrated facies is used.With the analysis of lithofacies and diagenetic facies,prediction charts of porosity and permeability in different sedimentary-diagenesis integrated facies are complied.By taking the sedimentary-diagenesis integrated facies in different depth as study objects,with the use of physical properties prediction charts of sedimentary-diagenesis integrated facies,on the basis of quantitative recognition of sedimentary-diagenesis integrated facies in single well,distribution profiles of sedimentary-diagenesis integrated facies as well as their spatial physical properties are established.Physical properties of bar sand bodies of Eocene Es4 s in southern gentle slope,Boxing sag are the best,with its porosity between 10% and 25%.The reservoir space are mainly intergranular pore and dissolution pore of feldspar.Capillary pressure curves leans to the left side.Physical properties of beach-ridge sand bodies are respectively better,with its porosity between 5% and 20%.The reservoir space are mainly intergranular pore and dissolution pore of feldspar.Capillary pressure curves leans to the middle side.Physical properties of beach-mat sand bodies are the worst,with its porosity between 2.5% and 12.8%.Capillary pressure curves leans to the upper-right side.On the basis of defining the physical properties limits,taking porosity-difference as an evaluation parameter for high-quality reservoir,controlling factor for high-quality reservoir of beach-bar sand bodies are determined.They are lithofacies,diagenetic facies and reservoir pressure.With multi-parameter classification of reservoirs under constraints of porosity differences and economic productivity of single well,reservoirs in beach-bar sand bodies of Eocene Es4 s in southern gentle slope,Boxing sag are classified.According to comprehensive classification scores,there are four types of reservoirs,and their distribution is pointed out.Shallow reservoirs are mainly of type ?and ?,and they are formed in the middle of thick sand bodies while type ? and ? are formed in thin sand bodies as well as thick bodies boundary where is near mudstone.Generally,reservoirs in shallow depth are of better connectivity.In the deep,distribution of type ?and ?becomes narrow while type ? and ? extends,and on the whole,reservoirs in the middle of thick sand bodies are relatively effective,and to direction of pinch-out boundary of sand bodies,reservoirs become less effective and reservoir heterogeneity becomes stronger.