Logging Evaluation Method Of Tight Gas Reservoir In Shahezi Formation Of W Fault Depression

The tight gas reservoirs of the Shahezi formation in W fault depression have complex rock types,multiple pore types,complex pore structures,poor physical properties and strong heterogeneity,which makes it difficult to calculate reservoir parameters and identify reservoir fluid properties.Therefore,it is necessary to carry out logging evaluation method research on tight gas reservoirs of the Shahezi formation in W fault depression to implement the development potential of tight gas resources and provide support for reserve prediction.According to the geological characteristics of the tight gas reservoir of the Shahezi formation in W fault depression,based on the core thin slices and logging information,it is clear that the rock types in the third and second members of the Shahezi formation are sandstone and conglomerate,and the rock types in the first member of the Shahezi formation are tight andesitic volcanic breccia and tight rhyolitic volcanic breccia,and then the conventional,ECS,natural gamma spectroscopy,imaging and other logging response characteristics of different lithologies are analyzed.The histogram method is used to select four and eleven lithological identification sensitive logging curves in the third,second members and the first member reservoirs respectively.Based on the sensitive logging response,three and fifteen lithologic qualitative identification plates are established for the two target intervals,respectively,and good application results are obtained.Based on the analysis data of mercury intrusion and nuclear magnetic experiments,the pore structure characteristics of the reservoir are analyzed,three types of volcanic reservoir types are divided,and the sensitive parameters of the reservoir type are optimized,so that six tight andesitic volcanic breccia and four tight rhyolitic volcanic breccia reservoir type identification plates are established.Using oil test data,core analysis porosity and permeability data,combined with conventional logging data,the physical property boundaries of three types of sandstone(conglomerate)reservoirs are determined,so that three sandstone(conglomerate)reservoir type identification plates are established,and the application results show that the effect of reservoir type identification is good.Based on gas test production data,combined with logging,gas logging and other data,the four-relationship of the reservoir is analyzed,and the sensitive logging parameters for fluid identification are optimized,so that five fluid identification charts are established for sandstone(conglomerate)reservoirs in the third and second members and five fluid identification charts are established for tight volcanic breccia reservoir in the first member of the Shahezi formation.By comparing with the oil test results,the qualitative identification rate of the fluid reached 80%.Based on the core analysis data and conventional logging information,the logging interpretation model of the shale content,porosity,and permeability of the reservoir are established separately by lithology.Using mercury intrusion test data combined with gas reservoir profile data in the study area,the logging interpretation model of the irreducible water saturation of the reservoir is established by the J-function method.Based on the analysis results of petroelectric law,considering the complexity of the pore structure of the tight volcanic breccia,the saturation model of the tight volcanic breccia reservoir is established according to the equivalent rock element theory and the effective medium symmetric conductivity theory.The comparative analysis shows that the equivalent rock element model saturation interpretation has the best effect.In view of the complex pore structure and muddy characteristics of sandstone(conglomerate),the improved Indonesian equation is cited,and a sandstone(conglomerate)reservoir saturation model based on the improved Indonesian equation is given.Using the logging evaluation method established in this paper,29 wells in the study area are actually interpreted,and the qualitative and quantitative interpretation results are compared with gas test production data,it is found that the interpretation coincidence rate is 83.3%.It shows that the established interpretation method is suitable for logging evaluation of tight gas reservoirs of the Shahezi formation in W fault depression.