Geological Stratigraphy and Spatial Distribution of Microfractures over Costa Rica Convergent Margin, Central America – A Wavelet-Fractal Analysis

Abstract

Abstract. Identification of spatial variation of lithology, as a function of position and scale, is very critical job for lithology modelling in industry. Wavelet Transform (WT) is an efficacious and powerful mathematical tool for time (position) and frequency (scale) localization. It has numerous advantages over Fourier Transform (FT) to obtain frequency and time information of a signal. Initially Continuous Wavelet Transform (CWT) is applied on gamma ray logs of two different Well sites (Well-1039 & Well-1043) of Costa Rica Convergent Margin, Central America for identifications of lithofacies distribution and fracture zone later Discrete Wavelet Transform (DWT) applied to DPHI log signals to show its efficiency in discriminating small changes along the rock matrix irrespective of the instantaneous magnitude to represent the fracture contribution from the total porosity recorded. Further the data of the appropriate depths partitioned using above mathematical tools are utilized separately for WBFA. As consequences of CWT operation it is found that there are four major sedimentary layers terminated with a concordant igneous intrusion passing through both the wells. In addition of WBFA analysis, it is clearly understanding that the fractal dimension value is persistent in first sedimentary layers and the last gabbroic sill intrusions. Inconsistent value of fractal dimension is attributed to fracture dominant in intermediate sedimentary layers it is also validate through core analysis. Fractal Dimension values suggest that the sedimentary environments persisting in that well locations bears abundant shale content and of low energy environments.