Kerogen-Bitumen-Porosity Nexus: Insights from Multi-Basinal Collocated SEM-Optical Light Petrography

Kelly, Shaina (ConocoPhillips) | Johnston, Michelle (ConocoPhillips) | Lee, Bernard (Innova Plex) | San Martin, Richard (FIB-X)


Abstract Robust links between unconventional pore-scale properties, organic matter, and production trends remain unclear, despite numerous pore-scale characterization studies from various petro-technical disciplines. Specifically, a clear and/or widely agreed upon understanding of kerogen-bitumen-porosity relationships is currently lacking. This work explores an interdisciplinary petrographic methodology to link organic pore-associations and habit to geochemistry and, ultimately, petrophysics. The method directly collocates (overlays) high resolution mosaic scanning electron microscopy (SEM) images with reflected white and UV/fluorescent light images (organic matter petrography analysis), enabling the identification of various kerogen maceral types and bitumen within the monochromatic SEM images. Mosaic SEM images are leveraged to help ensure the statistical representativeness of the characterized area. The consistent application of this integrated imaging workflow across various rock types, maturity, and basins has enabled foundational insights into specific organic-matter porosity associations and trends. Introduction Understanding unconventional reservoirs requires examining the porosity and permeability hosted within the mudrock-based (clay and silt-sized grains; includes claystones, mudstones, chalks, siltstones, shales, etc.) stratigraphy of the petroleum system, typically characterized by low porosity and low permeability. Organic porosity, specifically, has been studied for less than a decade, and there is currently a lack of clear understanding of organic porosity development in unconventional mudstone reservoirs (Katz and Arango, 2018). Due to the small nature of the pore sizes, scanning electron microscopy (SEM) is one method used to characterize nanoporosity hosted in the mineral matrices and/or organic matter (Loucks and Reed, 2014). However, SEM is limited in the ability to differentiate between different organic macerals, or individual organic matter constituents, found in the examined organic-rich shale/mudstone. Traditional methods for definitive organic matter determination include organic petrographic analyses using standard incident white light and UV microscopy under oil immersion. Organic petrography is limited to lower magnifications, approximately 50x magnification, compared to the high-magnification possible with SEM, allowing for resolutions up to approximately 2.5 nm/pixel and, correspondingly, pore features of around 5-10 nm.

  Geologic Time:
  Industry: Energy > Oil & Gas > Upstream (1.00)

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