Research On Characteristics Of The Low Permeability Reservoirs Of The Liushagang Formation In Fushan Sag

With the deepening of exploration in Fushan Oilfield,the high porosity and permeability area has been basically proved and entered the stage of oil and gas production.The oil and gas reserves in low permeability area have been paid attention to.Therefore,the oil and gas exploration and development in Fushan Sag has changed to the low permeability reservoirs with medium and deep layers and poor physical properties.Therefore,this paper carries out petrological characteristics,sedimentary microfacies,pore throat structure,diagenesis,reservoir physical properties,reservoir rock brittleness of low permeability reservoirs in Fushan Depression,and carries out classification and comprehensive evaluation of sandstone reservoirs in Liushagang Formation based on actual oil testing data.The rock composition and structural characteristics of reservoirs are analyzed by using the identification data of conventional rock slices,casting slices,clay mineral data and grain size report data.Through atmospheric pressure mercury data,nuclear magnetic resonance?NMR?,CT scanning and casting slices,the pore throat structure characteristics of reservoirs are analyzed.On the basis of previous studies,it can be divided into diagenetic stages.The sedimentary microfacies of reservoir is determined by combining core data and logging data,and the influencing factors of reservoir physical properties are analyzed.Reservoir sandstones of Liushagang Formation and Liujie Formation in Fushan Depression are well developed,mainly lithic sandstones.Reservoirs are mainly thin and medium-thick layers.Rock particles are mainly medium sand and fine sand.Grain size grinding roundness is mainly sub-edge-sub-circle and sub-circle.The brittleness index is higher.The first member of Liuyi is mainly in the A₁ substage of the middle diagenetic stage,while the second and third members of Liuyi are mainly in the A₂ substage of the middle diagenetic stage.The pore types of reservoirs are mainly primary intergranular pore and secondary dissolution pore.The pore size is mainly medium pore,and the throat is micro-throat,and nano-throat is the main throat.Reservoir physical property mainly develops pore and permeability types of ultra-low porosity,low porosity,ultra-low permeability and ultra-low permeability.Sedimentary facies is the main controlling factor of reservoir physical properties.