Modified method for estimating petroleum source-rock potential using wireline logs, with application to the Kingak Shale, Alaska North Slope

Abstract

In 2012, the U.S. Geological Survey completed an assessment of undiscovered, technically recoverable oil and gas resources in three source rocks of the Alaska North Slope, including the lower part of the Jurassic to Lower Cretaceous Kingak Shale. In order to identify organic shale potential in the absence of a robust geochemical dataset from the lower Kingak Shale, we introduce two quantitative parameters, $\Delta DT_\bar{x}$ and $\Delta DT_z$, estimated from wireline logs from exploration wells and based in part on the commonly used delta-log resistivity ($\Delta \text{ }log\text{ }R$) technique. Calculation of $\Delta DT_\bar{x}$ and $\Delta DT_z$ is intended to produce objective parameters that may be proportional to the quality and volume, respectively, of potential source rocks penetrated by a well and can be used as mapping parameters to convey the spatial distribution of source-rock potential. Both the $\Delta DT_\bar{x}$ and $\Delta DT_z$ mapping parameters show increased source-rock potential from north to south across the North Slope, with the largest values at the toe of clinoforms in the lower Kingak Shale. Because thermal maturity is not considered in the calculation of $\Delta DT_\bar{x}$ or $\Delta DT_z$, total organic carbon values for individual wells cannot be calculated on the basis of $\Delta DT_\bar{x}$ or $\Delta DT_z$ alone. Therefore, the $\Delta DT_\bar{x}$ and $\Delta DT_z$ mapping parameters should be viewed as first-step reconnaissance tools for identifying source-rock potential.