Quantification of organic content in shales via near-infrared imaging: Green River Formation

Abstract

We demonstrate the applicability of near-infrared (NIR) imaging for quantifying the spatial distribution of kerogen content in organic-rich shales with sub-millimeter resolution over cores that can span hundreds of feet in depth. We develop models that are validated for the thermally immature oil shale of the Mahogany zone in the Green River Formation. They utilize either all or part of the NIR reflectance spectrum thereby providing some flexibility in the choice of instrumentation and, thus, cost. The models accurately recover fine-scale (sub-millimeter) variabilities in kerogen content from calibrations to a few coarse-scale (centimeter to meter) measurements, a process known as downscaling. This obviates slow, costly, and discrete fine-scale measurements in favor of a rapid, inexpensive, and continuous mapping approach. It also has implications for mapping thermo-hydro-mechanical properties of organic-rich shales, given that they strongly depend on kerogen content. Since our models utilize kerogen-specific absorption bands, they may also find use in other hydrocarbon-bearing source rocks.