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Paleokarst Reservoir Seismic Facies Classification Using Frequency Spectral Decomposition, Machine Learning and Electrofacies Constrained Approach

Abstract

More than 1.5 billion tons of hydrocarbons have been found in the Central Tarim basin, which are mainly stored in caves, vugs and fractures. Seismic characterization of such carbonate reservoirs is real challenging for geophysicists because of the deeply buried depth, interior structures and fine scales. Conventional qualitative descriptions of the internal structure and geometry of seismic reflections can’t meet the requirements from geological modeling and reservoir simulations. Based on frequency spectral decomposition, electrofacies and machine learning techniques, a new quantitative seismic facies analysis approach was developed, whose procedure is sequential according to the different seismic reflections, and has successfully applied for reservoir characterization.

Based on geological understanding and related seismic reflections, the seismic facies analysis was divided into four steps: 1) First, we employ continuous short-time Fourier transform to divide high, middle, and low frequency components of seismic data to quantitatively predict reservoirs with different scales; 2) The amplitude, acoustic impedance, RMS, chaos, variance, and sweetness etc., were used as input seismic datasets. Supervised machine learning method was used for the strong amplitude analysis, in which we used cores and electrofacies interpretations as prior knowledge; 3). Unsupervised machine learning method was used for weak amplitude seismic facies classification and the resulted seismic facies were interpreted by electrofacies near boreholes. 4). 6 seismic facies were classified, and their spatial geometry were delineated and analyzed with faults and unconformity distributions.

Our integrated approach honored seismic frequency, multi attributes and multi scale combinations among geology-well logging-seismic data, classified seismic facies quantitatively, provided an accurate overall solution for paleokarst reservoir characterization, and can be applied to similar sedimentary basins that accommodate deeply buried carbonate reservoirs affected by karstifications and faults.