Logging Research On Key Parameters Of Shale Gas In Yanchang Formation, South Central Ordos Basin

The shale gas resource is rich in Yanchang formation, South Central Ordos Basin, but compared with the foreign and domestic shale gas and conventional natural gas, the geological characteristics and logging response characteristics of shale gas is obviously special. Because of the limitations of the data of core analysis, lithology and mineral composition of shale gas reservoir is complex, physical property is poor, the logging research on key parameters of shale gas faces many problems, such as the optimization of logging series and the applicability of logging interpretation method, etc. Therefore, in this paper, through the analysis of core data and its logging response characteristics, combined with the elemental capture spectroscopy logging and NMR logging interpretation results, systematically studies the geological characteristics and its logging response characteristics of shale gas reservoir, established logging interpretation model of the clay content, total organic carbon content, thermal maturity, porosity and gas content and other key parameters, provides theoretical basis for the logging evaluation of shale gas.The shale organic carbon content is higher, the type of organic matter is suitable, the thermal maturity is moderate; the types of shale minerals are mainly clay minerals and quartz, feldspar minerals, pore types are mainly intergranular pores, intergranular pores and holes, and pore structure is complex, reservoir is dense, shale gas content is mainly adsorbed gas content, free gas content is less.The normalized density and neutron difference method, natural gamma relative values method were used to established the logging interpretation model of shale content, and the calculatied shale content and X diffraction experiment results, ECS logging interpretation results are consistent. Then according to the analysis of whole rock X diffraction results and the calibration logging information, interpretation model of rock multi mineral is established, and quantitatively predicte mineral content of shale.Through the analysis of total organic carbon content and its response characteristics of uranium, natural gamma, acoustictime, density, neutron and resistivity logging, optimum sensitivity parameters of natural gamma relative value, acoustictime and organic carbon content were analyzed by multivariate linear regression analysis, and the organic carbon content interpretation model was established, the correlation coefficient can reach more than 0.8. According to the neutron and density overlap graphs reflect the vitrinite reflectance, based on ALgR and TOC crossplot to determine the thermal alteration index, in order to reflect the thermal maturity.Using acoustictime, density, neutron and natural gamma relative value of multiple linear regression analysis with the porosity, porosity interpretation model is established, the correlation coefficient can reach more than 0.8. After Eliminating the crack sample permeability values, using the weighted average permeability and layer analysis porosity permeability to establish permeability interpretation model, and the correlation coefficient can reach more than 0.6.According to the desorption experiments, isothermal adsorption experiment, litho electric experiment and logging analysis method, established the shale gas content interpretation model, estimated the total gas content, adsorption gas content and free gas content. Among them, total organic carbon content has greater effect on adsorption gas, according to the organic carbon content analysis, the precision of the interpretation model of adsorption gas content was more than 0.8; while the free content and porosity are closely related, the precision of the free content logging interpretation model established by litho-electric experiment and logging analysis methods is higher. According to the above two methods, the gas content, the free gas content and the total gas content are consistent with the interpretation results of ELAN logging interpretation.