Well Logging Evaluation Of Tight Sandstone Gas In Wubao Area,Ordos Basin

As an important pillar for increasing storage and production in the field of unconventional natural gas in China in recent years,tight sandstone gas is of great strategic importance.Therefore,this paper aims to interpret and evaluate the lithology,pore permeability,gas content and compressibility of the tight sandstone gas reservoir in the study area by means of logging and petrophysical experiments,with the aim of providing a reliable basis for the exploration and development of tight sandstone gas in the study area.The geological characteristics of the reservoir are the basis for logging interpretation.Based on the petrophysical experiments such as thin section analysis and scanning electron microscopy,it is clear that the main rock type in the study area is quartz sandstone,with medium to fine sandstone in general,and the sandstone porosity is mainly distributed between 1.5～4.5%,and the permeability is mainly distributed between 0.01×10-3～0.3×10-3μm2.The key parameters such as lithology identification,mud content and pore permeability of the reservoir are the key work of logging interpretation and an important basis for the next evaluation.Specifically,we confirmed that the suitable mud content solution method for the study area is natural energy spectrum method;we established the porosity solution model for sandstones with different grain sizes;we established the Coates-based permeability solution model using NMR logs and experimental data;and we established the saturation solution model based on the Indonesian formula.In order to identify gas formations more accurately,after comparing several methods,it is concluded that the NMR logging method based on the difference spectrum method and the shift spectrum method is the most accurate,especially for the identification of gas content in microporosity;the method based on array acoustic logging is not affected by the rock size,and the identification effect is better;the three-porosity logging overlap method is only applicable to the identification of gas content in coarse sandstone formations,and the overall gas content indication of array induction logging is not These two methods can only be used as auxiliary methods.In terms of compressibility evaluation,we first clarified the idea of calculating rock elasticity parameters based on longitudinal and transverse wave velocities and established a conversion model of longitudinal and transverse wave velocities and dynamic and static elasticity parameters,and then constructed a gray correlation-based brittleness index calculation model by integrating the mineral fraction method and Poisson-Young method;a combined spring model was used to calculate the horizontal stress difference coefficient in the study area.In summary,it is concluded that priority shot-hole test mining is recommended in the low Poisson’s ratio,high Young’s modulus,high brittleness index and low horizontal stress difference layer section.Finally,the results of the above studies were synthesized,and a comprehensive interpretation and evaluation of logging was carried out for three key wells,W75,W74 and W38,in the Benxi Formation formation.Compared with the original interpretation conclusions,the new interpretation method improves the interpretation accuracy and proposes a shot-hole gas test for the 63rd formation of W38 well.