The Study Of Electrical Properties In Tight Carbonate Reserviors Based On The Characterization Of Pore Structure

The gas saturation of the Reservoirs is a key parameter to evaluate the gas reserves.However,the microscopic pore structure of tight gas reservoirs is complex.Many micro and nano-scale pore throats are developed.Because of the strong heterogeneity of reservoirs,the low porosity and permeability,which cause new challenges for accurating the evaluation of gas saturation.At present,we can use the rock electricity experiments and the data of the saturation log interpretation to obtain the gas saturation.However,the understanding of the microscopic pore structure characteristics of tight carbonate rock reservoirs is incomplete.Therefore,an experimental and theoretical study on the relationship between electric parameters of tight carbonate rock based on the pore structure characterization have been carried out which have a great significant to the Log interpretation and gas saturation in complex reserviors.In this paper,the typical tight carbonate reservoirs in China are studied.Combined with various pore structure characterization methods and rock electricity experiments,the microscopic pore structure of tight carbonate reservoirs and the resistivity increase coefficients at different water saturations are analyzed.At the same time,the infacts of the two resistivity models which compared with the experimental data were analyzed.The optimal model was used to evaluate the saturation of gas saturation in different area.The main research work of the thesis and related knowledge are as follows:(1)Based on experiments of pore structure,including cast thin sections,scanning electron microscopy,constant-rate mercury injection,and nuclear magnetic resonance(NMR),which the pore-throat microstructure was identified,and the average pore throat radius and coordination number of the dense carbonate reservoirs were obtained.The pore size distribution,pore throat radius,coefficient of variation,hydraulic radius and other pore structure parameters were obtained from the T2 spectrum.(2)During the experiment of rock electricity,the Nuclear magnetic T2 spectra of different water saturations were measured by nuclear magnetic resonance(NMR).The pore throat radius distribution and the normalized hydraulic radius and water saturation Rvw/Rv-Sw were obtained from the nuclear magnetic T2 spectrum,which the geometric factor at of the change of pore fluid was obtained.(3)Based on LBT and resistivity theoretical model of tight shale-rich and calcite-rich carbonates,single factor analysis of coordination number Zv,variation coefficient ?v/<r>,and shale content Vsh,the geometric factor at,and other related parameters which increase the resistivity were analyzed to understand the main factors that affect the conductivity of reservoir rock.(4)The Rock-electricity experiments were conducted by gas flooding to establish the relationship between formation factor F and porosity ?,resistivity increase coefficient I and water saturation Sw,and then,the experimental data were modeled in power logarithm with double logarithmic coordinates which we can obtain the a,b,m,and n values of 14 rock samples in G and H regions.At the same time,the change characteristics of the relevant pore structure parameters to the rock electrical parameters are analyzed.(5)By obtaining the LBT resistivity model and the related parameter values of the mud-containing and calcium-containing models,the theoretical resistivity values are compared with the experimental data to verify the model's adaptability.To use the LBT oil-gas saturation calculation model which we can log the gas saturation of reservoir,compare and analyse with Archie log interpretation,and then conduct the analysis of th variance.Based on the research of the experiments and theoretical knowledge of the resistivity model in this paper,we understand the microscopic characteristics,I-Sw curve characteristics,and the infacts of rock electrical parameters,complete saturation and T2 spectrum characteristics after displacement of tight carbonate reservoirs.The secondary logging interpretation of gas saturation lays the foundation for comprehensive evaluation and development of reservoirs.