Research On Microscopic Pore Structure And Saturation Parameters Of Low Permeability Sandstone

With the research deepening of unconventional oil and gas exploration and development,the low permeability sandstone reservoirs gradually become an important replacement target of conventional fossil energy.Affected by complex sedimentary environment,reservoir-forming mechanism,structure,diagenetic process.low permeability sandstone rock types are diverse,microscopic pore structure is complex,reservoir effectiveness identification and saturation accurate calculation is difficult.It has become the primary problem of low permeability sandstone reservoir evaluation and prediction.The article takes the low permeability sandstone of Shahejie Formation in Dongying Sag for research object,based on a variety of test and analysis methods,such as core description,casting thin slice,X-ray diffraction,physical property,mercury penetration,nuclear magnetic resonance,nitrogen adsorption experiments,the pore structure characteristics.type classification.reservoir effectiveness and saturation parameter analysis and calculation of low permeability sandstone are studied.(1)According to the testing data,extracting the pore structure parameters from the T2 spectrum and capillary pressure curve,and based on the relationship between the pore structure parameters and physical parameters,the pore structure of low permeability sandstone is divided into 3 categories and 5 subcategories according to the standard of clastic reservoir division.On this basis,the pore types and structural characteristics of different pore structures were systematically analyzed by fully excavating the information in thin section data,mercury injection,nuclear magnetism and nitrogen adsorption data.(2)According to the characteristics of reservoir formation and thin interbedded deposition in the study area,the relationship between oil saturation and pore structure parameters is analyzed in detail,and there is a positive correlation between pore structure and oil saturation.(3)Based on Autoscan permeability test and physical property data,the relationship between reservoir effectiveness and uniformity and concentration of pore distribution is deeply analyzed.Mercury injection method and nitrogen adsorption method were used to characterize the full pore size of effective samples(oil immersion)and invalid(oil free)samples.and the lower limit of pore size of effective reservoirs was determined.Combined with mercury injection method and positive and inverse accumulation method,the lower limit of physical properties of effective reservoir is determined.(4)The influence of pore structure on rock electrical parameters is discussed by means of rock electrical experiment fitting and single sample data analysis,and it is proved that pore structure type has a strong influence on rock electrical parameters.Then,on the basis of pore structure classification,the logging response information of different pore structure strata is statistically analyzed,and a chart for identifying pore structure types of logging information is established.(5)Finally,the pore structure identification chart is established by using the sensitive parameters of T2 spectrum of nuclear magnetic resonance,and the sensitivity of T2 pore structure parameters to different types of reservoirs is verified,and then the formula for calculating the electrical parameter M of rocks with different pore structures is established from the peak value of T2 spectrum.The classification is applied to the saturation calculation of wellbore section,which effectively improves the accuracy of reservoir validity identification and saturation calculation.and is also helpful to the fine identification of fluid properties and accurate estimation of reserves in complex low permeability sandstone reservoirs.The method presented in this paper increase the accuracy of reservoir effectiveness evaluation of low permeability sandstone,and combine the geological information and logging closely,the study provides evidence for compute reserves and development in low permeability sandstone reservoir in south slope of Dongying Depression.