Methods Of Pore Structure Characterization And Fine Well Logging Evaluation In Heterogerneous Clastic Reservoir

The rapid increasing demand osf oil and gas makes the exploration and development ofcomplex heterogeneous clastic rock reservoir more important. The heterogeneous clastic rockreservoir shows strong anisotropy and complex pore structure,which made the seriouslynonlinear relationships between formation parameters and reservoir logging responses.Finelog interpretation and productivity predictions of such reservoir faces great difficults givingreasons above. Therefore, it is significant to study the effective comprehensive logginginterpretation and evaluation method for the heterogeneous clastic rock reservoir, providingtechnical supports for successness of oil&gas drilling and perforating production engineering.Applying image processing,geological statistics,topology methods etc, thin section and BSEimages are analyzed to get more detailed pore structure imformations contiained,which breakthrough geologists’ limitations of the qualitative or semi-quantitative methods.Microscopicpore structure parameters obtained give us deeper understanding and evaluation ofheterogeneous clastic rock.The paper introduces PGSE sequence to investigate the diffusion characteristics of fullywater filled rocks. Parameters such as average specific surface area, surface relaxation rateand tortuosity are obtained by PGSE-CPMG experiments, what’s more, absolute pore radiusdistribution are reached and comparisons among mercury intrusion and thin sectionprocessing are carried out.Result shows that absolute pore radius distribution obtained byPGSE-CMPG has great similiarity with with data obtained by thin section processing.T2weighted map is investigated by Nuclear Magnetic Resonance Imaging(MRI) whichusing spin echo sequences(SE). T2spectrum is reached by double-exponential fitting of NMRdecay signal in singel pixel and adding of the total slice.Comparing to1D NMR T2spectrum,the MRI T2spectrum has great advantages in characterization of fast relaxtion groups, which reflects pore structure more precise. Multi-slices T2weighted maps are achived by sliceselection gradient and heterogenetic index for different directions are obtained by variogramfitting,where first order spherical model. Experiments results show that the heterogeneousindex increases with the increasing of heterogeneous degree of core sample.By introducing fractal theory, fractal dimensions calculated by capillary pressure, binaryimage prcessing and NMR are campared. Pore structure becomes more complex with higherfractal dimension. Appling correlation theory to optimize optimum characterizationparameters of pore structure from microscopic parameters of image processing, geostatisticsand geometric topology, the microscopic parameters of NMR and MRI and fractal dimension.With the combination of information entropy and fuzzy spectral clustering algorithm,automatic classficitaion of pore structure types and optimal classification sample sets arereached meanwhile.to make automatic classification of core pore structure to obtain theoptimal classification samples. Based on core calibration logging, kernel principal copmonentand support vector classification method (KPCA-SVC) are used to recognize pore structruretypes automatically using conventional well logging data.The results show successfully.Considering nonlinear problems between core porosity and logging responses inheterogeneous clastic rock reservoir,the paper introduced kernel-support vectorregression(K-SVR) to realize nonlinear mappings between core porosity and loggingresponses,which gives more accurate calculation results. Absolute permeability models arebuilded and compared based on pore structure and percolation theory respectively. Resultsshow that the model based on percolation theory has higher precision than that based on porestructure type. Getting the relationship between absolute permeability and overburdenpressure according to pore structure type makes transition between laboratory and formationpermeability. Compared with five different bound water saturation respectively, the paperestablised bound water saturation model based on NMR and improved Timur’sformula.According to two-phase fluid flow theory and the reciprocal of seepage and currentfield, oil and water relative permeability model are constructed for different pore structure type,where saturation and electrical parameters are included.Complex conductive characteristics and unclear understanding of the changing rule ofrock electrical parameters affect saturation modeling due to complex pore structure.Introducing fractal theory and considering influences of porosity and clay, salinity andwettability on electrical properties, cementation exponent and resistivity index formula areestablished based on Archie’s equations. Systematically analysis of change rules of rockelectrical parameters in different formation conditions are conducted.The paper proposesdynamic rock electrical parameter model combined with experiment based on ’simplefitting-correction method’ and investigates parameters in model for different pore structuretype.Fluid sensitive parameters are established based on precise calculation of reservoir andfluid parameters. Combination of Optimal parameters determined by crossplot technique andFisher discrimination make the fluid type identification successfully. Oil-water contact depthis precisely determined by Multi-resolution wavelet analysis of the first kernel principalcomponent of well logging data(KPCA1) and comparing energy spectrums differencenearby.The result shows that by six degree wavelet decomposition of KPCA1, it is easily toget oil-water contact depth comparing with energy spectrum difference between five and sixdegree. With intensive investigation of production data, the productivity index per meter ispredicted accurately.The productivity classification scheme is established in combiation of theproductivity index per meter and pore structure types,which provide technical support forconstruction scheme of heterogeneous clastic rock reservoir.