Study On Pore Structure Of Tight Sandstone Of The 4^th Member Of Shahejie Formation In G89 Area,Dongying Sag

Tight sandstone reservoirs in the lower section of the upper of the 4^th member of Shahejie Formation is an important target of oil and gas exploration in high 89 area of Dongying sag,its geological reserves are rich,sandstone and mudstone thin interbreeds,reservoir heterogeneity is strong,and pore structure is complex.The pore structure of the reservoir directly affects the storage and flow capacity of the reservoir.In this paper,the pore structure is studied from petrological characteristics,reservoir space characteristics,pore throat radius distribution and stress sensitivity,based on a variety of test and analysis methods,such as casting thin slice,SEM,X-ray diffraction,image analysis,high pressure mercury and overburden-pressure porosity-permeability experiments.According to the casting thin slice,SEM and X-ray diffraction data,the major sandstone type is powder-fine feldspathic lithic sandstone.Roundness is mainly for the subangular,sorting medium-poor,point-line contact,porous cementation.The rocks have high interstitial material includes argillaceous matrix and calcite,dolomite and clay mineral,and the clay mineral type is mainly illite/smectite mixed layer and illite.Through the observation of the cast thin slice and SEM,reservoir space mainly includes inter-granular dissolution pores,debris dissolution pores,feldspar pores and inter-crystal pores.The type of pore throat mainly includes sheet and bend sheet throat,bundle-like throat.The pore diameter and the number distribution of the pores were quantitatively analyzed by casting thin slice and image analysis,the pore diameter of the study area is mainly distributed in the range of 1¹0?m,the contribution rate of the pore to face rate is 82.39% less than 50?m.According to high pressure mercury data and overburden-pressure porosity-permeability experiments,analyzed the characteristics of capillary pressure curve and stress sensitivity of specimens with different capillary pressure curves,combined with physical,petrological characteristics and stress sensitivity,the reservoir pore structure is divided into three types.Type ?: the displacement pressure is 0.35 1.21 MPa,the median pressure is 2.53 4.31 MPa,the porosity is 7.8% 15.4%,the permeability is 0.044 2.311 × 10^-3?m²,the average throat radius is 0.3 0.811?m,the reservoir space mainly includes inter-granular dissolution pores,debris dissolution pores and feldspar pores,the content of interstitial material is 7% 15%,and stress sensitivity is weak.Type ?: the displacement pressure is 4.65¹2.04 MPa,the median pressure is 28.35⁵1.12 MPa,the porosity is 3.2% 12%,the permeability is 0.003 0.025×10^-3?m²,the average throat radius is 0.03⁰.065?m,the reservoir space mainly includes inter-granular dissolution pore,dissolution micro-pore and inter-crystal micro pore,the content of interstitial material is 14%²2%,and stress sensitivity is strong.Type ?: the displacement pressure is 45 46 MPa,the median pressure is 73.02 125.22 MPa,the porosity is 4.4% 8.8%,the permeability is 0.016 0.028×10^-3?m²,the average throat radius is 0.008⁰.011?m,the reservoir space mainly includes dissolution micro-pore,inter-crystal micro pore and filling ingredient pore,and stress sensitivity is strongest.