Reservoir effectiveness evaluation and new fluid identification method of Maokou Formation carbonate rocks in southern Sichuan Basin
The interval from the second member to the top of the Permian Maokou Formation in southern Sichuan Basin is dominated by limestone reservoir with developed fractures and vugs and strong heterogeneity,which has complex resistivity response mechanisms and faces difficulties in reservoir effectiveness evaluation and gas/water layer identification.In order to effectively evaluate the fractured-vuggy carbonate reservoir and improve its fluid identification accuracy,this paper studies the characteristic parameters such as conventional resistivity curves and means and variances of electrical imaging logging porosity spectrum based on physical property modeling,to classify reservoir effectiveness.A comprehensive fluid identification index is established by applying the synthetic S-wave time-difference stacking method,the P-S wave velocity ratio overlap method,and the P-S wave equivalent elastic modulus difference ratio method.Additionally,fluid identification is researched based on the means and variances of resistivity spectrum.The following results are obtained.First,it is for the first time that a reservoir effectiveness classification index(AVRT)is established by using parameters such as the normalized resistivity curve of sliding variable windows and the mean and variance of electrical imaging porosity spectrum.According to the classification standard,the reservoirs are classified into three types,and 155 intervals in the study area are interpreted,with a logging interpretation coincidence rate reaching 91.1%.Second,a fluid identification index is constructed based on the weighted average of multiple methods such as the synthetic S-wave time-difference stacking method,the P-S wave velocity ratio overlap method,and the P-S wave equivalent elastic modulus difference ratio method,and its coincidence rate of reservoir fluid identification is 85.7%.Third,a fluid identification chart based on AVRT and mean apparent formation water resistivity spectrum is developed based on the influencing mechanism of each parameter on fluid type,combined with the mean and variance of apparent formation water resistivity spectrum.It is verified to have a coincidence rate of reservoir fluid identification up to 100%.In conclusion,in the new method,the normalized resistivity of sliding variable windows can highlight the thin layers with high reservoir quality,and the fluid identification index can better identify weathered crust and fractured-vuggy gas reservoirs.This new method significantly improves fractured-vuggy carbonate reservoir evaluation and its fluid identification accuracy,and effectively overcomes the difficulties in fluid identification in fractured-vuggy carbonate reservoirs of strong heterogeneity.
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维普
