地质科技通报 (Jul 2021)
Application of wavelet transformation of logging data in sequence stratigraphic division of Cambrian Xixiangchi Group in Central Sichuan Basin
Abstract
Due to the lack of biological fossils and small changes in lithology and electrical properties of the Cambrian Xixiangchi Group in central Sichuan Basin, it is difficult to accurately divide sequences by using traditional core and logging data.The abrupt points of Th, U and K curves of natural gamma-ray spectrum logging can indicate sequence interface and maximum flooding surface, and their Th/U and Th/K curves can reflect not only the redox environment during deposition, but also the change of sedimentary water body and record the sedimentary cycle.Then multi-scale decomposition is carried out by wavelet transformation technology, and the wavelet curves of different series are obtained.Taking Well GT2 as the main research object, the Th/U curve is decomposed by multi-wave basis, and it is found that Dmeyer wavelet is the best.Combined with the carbon isotope positive drift event, based on the Th/U-d8 analysis of the wavelet curve obtained by wavelet transformation, two kinds of sequence division geological models are summarized, and the Xixiangchi Group is divided into 4 third-order sequences and 8 individual systems tracts. Each third-order sequence is composed of transgression systems tracts and high-stand systems tracts.At the same time, the higher resolution wavelet curves Th/U-d7 and Th/U-d6 curves are selected to finely divide the fourth-order and fifth-order sequences, which are divided into 11 fourth-order sequences and 25 fifth-order sequences, and the relative sea level changes during the sedimentary period are described by third-order sequences and fourth-order sequences respectively.This study is helpful to the fine sequence division of Xixiangchi Group in central Sichuan Basin and promote the study of its sedimentary evolution and reservoir development characteristics.
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