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Fine lithology and sedimentary facies prediction of carbonate based on the amplitude attribute of converted shear wave

Abstract

Dolomite reservoirs are generally developed in the Lower Permian limestone strata in Sichuan basin. In the seismic section of PP wave, response of dolomite is not obvious, which limits the prediction accuracy of lithology and sedimentary facies. In order to excavate the potential of multi-wave (PP and PS) seismic data in reservoir prediction, we carried out the detailed analysis of the multi-wave seismic data of the target layer, it was found that the amplitude of converted shear wave (PS) is generally higher than that of compressed wave (PP), and this feature is more obvious in area of reservoir not developed. In order to explain it reasonably, we carried seismic forward modeling of PP and PS wave with typical wells, and it turned out that the amplitude of PS wave is strong while that of PP wave is weak, which is consistent with the actual seismic section. Further we build lithology identification template about the three major lithology such as argillaceous limestone, limestone and dolomite by means of petrophysical modeling, also performed fine lithology interpretation with logging data. By the above analysis, we can get that the feature of stronger amplitude of PS wave while strong amplitude of PP wave is the response of argillaceous limestone contained in limestone, which can be interpreted as the argillaceous limestone development area, indicating the low-energy beach or the beach sea microfacies. And the feature of stong amplitude of PS wave while weak amplitude of PP wave is the response of dolomite contained in limestone, which can be interpreted as dolomite favorable reservoir development area, indicating the high energy beach microfacies. And the rest of other weak reflection features of PS wave can be interpreted as a transition type. Based on the above understanding, we selected proper time window to extract the maximum peak amplitude of the PS wave in the target layer. The high value represents area of argillaceous limestone developed, indicating the low-energy beach or the beach sea. The low value represents area of dolomite developed, indicating the high energy beach. The lithology and sedimentary microfacies distribution characteristics predicted by PS wave are in good agreement with the reservoir prediction results by seismic inversion and attenuation attributes of PP wave, so it can be get that PS wave has obvious advantage in detailed characterizing carbonate lithology and sedimentary facies than that of traditional PP wave.