--> Rapidly Assessing Materiality and Commerciality in Organic-Rich Mudstones by Linking Geochemical Responses Back to Corresponding Acoustic and Geomechanical Rock Properties

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Rapidly Assessing Materiality and Commerciality in Organic-Rich Mudstones by Linking Geochemical Responses Back to Corresponding Acoustic and Geomechanical Rock Properties

Abstract

Within academia, linkages have been made between organic matter burial and how it impacts biogeochemical cycles affecting oceanic & atmospheric evolution over the past 3Ga through the use of major and trace element geochemistry. This concept can be expanded to investigate linkages between organic matter burial and how it controls geochemical rock properties that directly impact the preservation of organic matter, as well as acoustic and geomechanical rock properties that directly impact the hydraulic fracturing and expected ultimate recovery of hydrocarbons from organic-rich mudstone reservoirs. The petroleum industry continues searching for a mudstone-based reservoir workflow to locate “sweetspots” consistently, similar to the use of amplitudes in sandstone reservoirs to quickly scan for material resources to enable rapid commercial decisions. It is clear that within mudstone-rich systems there are limitations of using density-neutron-resistivity logging to identify reservoir quality and completion quality. Instead we suggest first using a straightforward Th/U vs. Ca/Si geochemical logging crossover plot to distinguish major rock types present within mudstone-rich environments. This enables the use of established petrophysical workflows based upon acoustic rock property responses from standard logging tools. The geochemical logging crossover plot also complements & enhances a straightforward Young's Modulus-Poisson's Ratio geomechanical crossover approach to break out rock strength contrasts between and within prospective rock types. The combination of geochemical, acoustic, and geomechanical logging datasets can be used to screen for zones of enhanced reservoir quality which overlap zones of enhanced completion quality beneficial for hydraulic fracturing and stimulation. Using this approach potential reservoir and non-reservoir zone can be quickly identified and evaluated, and horizontal target zones can be ranked based on reservoir and completion quality assessments. This workflow was applied in a number of unconventional plays around the world to identify rock types and their relationship with their corresponding acoustic (Vp/Vs and AI) and geomechanical (YM, Shmin, PR) log responses. This has enabled creation of calibrated seismic inversion cubes to identify occurrence of highest quality pay and lithologies that could impede hydraulic fracture extension.