Optimizing Permeability Qualification in Thinly Laminated Sand-Shale Sequences with Sonic Dispersion Frequency Analysis

Abstract Thinly laminated reservoir characterization, particularly in terms of sand laminae thickness and permeability, is crucial for estimating zonal net pay thickness and evaluating the commercial viability of hydrocarbon discovery. Accurate assessment of thinly laminated reservoir net pay thickness and permeability necessitates a comprehensive suite of open hole logs, including Gamma Ray, Neutron-Density, Resistivity, Sonic, and NMR logs. This paper explores an innovative application of utilizing sonic logs data dipole dispersion frequency analysis to swiftly identify probable permeable pay zone thicknesses for thinly laminated reservoir. Conventional analysis utilizing basic logs such as Gamma Ray, Density, and Neutron responses, often poses challenges to accurately delineate thinly laminated reservoirs. However, dipole dispersion frequency analysis offers a breakthrough by leveraging the low-frequency limit of the dispersion curve to estimate formation shear slowness, which accurately reflects true formation slowness. By generating a frequency-slowness coherence log from recorded waveforms at each depth, we can effectively indicate zonal thickness and derive a pseudo permeability measure, facilitating rapid decision-making for testing. Our study traces the higher frequency limit of the flexural wave to obtain a slowness whose response is related to formation permeability. The width of this frequency band, which is high frequency slowness minus low frequency slowness, serves as a qualitative indicator of formation properties, such as lamination and reservoir permeability. Notably, in shale zones, the frequency width is significantly narrower compared to reservoir zones, providing a clear and striking contrast that indicates the amount of permeable sand in various layers. This analysis enables quick identification of permeable zones, significantly enhancing testing efficiency. The findings presented in this abstract are based on extensive work across a laminated reservoir field, demonstrating clear identification of zonal and permeable thicknesses corroborated by borehole images and formation testing. This innovative approach has the potential to revolutionize reservoir characterization, offering a rapid and reliable method for permeability assessment in laminated sand-shale sequences.