Study On The Characterization Of Pore Structure Of Tight Sandstone Of Shahejie Formation In Block Fan 154,Dongying Sag

With the developments of the theory and technology of hydrocarbon exploration,tight sandstone oil reservoir attracts more and more attention recently.Tight sandstone oil reservoir heterogeneity is strong,and pore structure is complex.The pore throat sizes vary from nano-scale to micro-scale.In order to study the characteristics of pore structure of tight sandstone of Shahejie Formation in Block fan 154,Dongying Sag,this paper analyses lithology,pore structure and pore type,based on the experiments of casting thin slice,the SEM,high pressure mercury injection,constant-speed mercury injection,nuclear magnetic resonance and so on,then made a classification for the reservoir of tight sandstone of Shahejie Formation in Block fan 154.According to observations of scanning electron microscopy?SEM?and casting thin slice and X-ray diffraction data,the tight sandstone of Shahejie Formation in Block Fan 154 is mainly fine lithic sandstone,middle sorting and psephicity,line contact,pore cementation.The content of interstitial material is high,which is mainly consisted of clay minerals.The pore types of reservoir are intergranular pore,intra-granular dissolution pore and inter-crystalline micro-pore.The throat types are mainly composed of flake,tortuous flake and tubular throat.The distributions of pore and throat were measured by constant velocity mercury injection.The pore radius is mainly distributed from 90?m to 200?m,but the volume of those pores is less 30% of the total pore volume.Throat radius is mainly distributed in 0.4?m²?m.The ratio of pore-throat ranges from 100 to 300.Because of the small size of throat radius and the high ratio of pore-throat,it is difficult for the fluid to flow and the development of reservoir.Based on the curves of T₂ spectra of sample saturated fluid and after centrifuge measured by nuclear magnetic resonance?NMR?experiments,a study was made on the characteristics of mobile fluid of reservoir.T₂ spectrum curves are unimodal both before and after centrifugal,and the pore spaces which relaxation time is between 10 ¹00ms are movable fluid spaces.The saturation of movable fluid of tight sandstone of Shahejie Formation in Block Fan 154 is 9.2%⁵2.2%.The movable fluid spaces are intergranular pores connected by submicron throats.Owing to controlled by nano-scale throat,the fluids in inter-crystalline micro pores and dissolution micro pores which are irreducible fluid.Based on the analyses of experiments of casting thin slice,conventional mercury injection,SEM and so on,this paper classified the reservoir into two types.Type ?—the porosity is 16.5²0.7%,the permeability is 0.062⁰.562×10-3?m²,the displacement pressure is 0.78².06 MPa,the median pressure is 3.25¹0.14 MPa,and the saturation of mobile fluid is 44.6⁵2.2%.the content of interstitial material is 9%¹2%,the mainly pores are intergranular pore,intra-granular dissolution pore and inter-crystalline micro-pore,the throat types are mainly composed of flake,tortuous flake and tubular throat.Type ?—the porosity is 9.96¹6.9%,the permeability is 0.006⁰.111×10^-3?m²,the displacement pressure is 2.23⁶.41 MPa,the median pressure is 11.54⁵4.85 MPa,and the saturation of mobile fluid is 9.2²5.8%.the content of interstitial material is 11% 28%,the mainly pores are residual intergranular pore,dissolution micro-pore and inter-crystalline micro-pore,the throat type is tubular throat.