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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, ∆DTx and ∆DTz , estimated from wireline logs from exploration wells and based in part on the commonly used delta-log resistivity (∆log R) technique. Calculation of ∆DTx and ∆DTz 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 that can be used as mapping parameters to convey the spatial distribution of source-rock potential. Both the ∆DTx and ∆DTz 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 ∆DTx or ∆DTz, total organic carbon values for individual wells cannot be calculated on the basis of ∆DTx or ∆DTz alone. Therefore, the ∆DTx and ∆DTz mapping parameters should be viewed as first-step reconnaissance tools for identifying source-rock potential. Introduction In 2012, the U.S. Geological Survey (USGS) completed an assessment of undiscovered, technically recoverable oil and gas resources in three source-rock systems (fig. 1) of the Alaska North Slope: (1) the Triassic Shublik Formation; (2) the lower part of the Jurassic to Lower Cretaceous Kingak Shale; and (3) the Cretaceous pebble shale unit, Hue Shale, and parts of the Paleogene Canning Formation, collectively called the Brookian shale (Houseknecht, Rouse, Garrity, and others, 2012). Maps of inferred source-rock richness were constructed using three parameters because of differences in lithology and wireline-log response among the source rocks. The map used for the Kingak Shale is highly generalized (fig. 2) because no quantitative mapping parameter had been defined. The study summarized in this report was initiated to evaluate the efficacy of the delta-log resistivity (∆log R) technique (Passey and others, 1990) for estimating an objective and quantitative parameter for evaluating source-rock potential from wireline-log data. This parameter may be useful as an evaluation tool for individual wells and, when calculated for multiple wells, as a mapping parameter. However, due to software limitations for digital calculation of ∆log R and the absence of a robust geochemical dataset for calibration of ∆log R, we sought to develop a modified version of ∆log R that yields two parameters that may serve as proxies of source-rock quality and volume. This report documents the digital workflow developed for calculating a modified version of ∆log R and presents the results of applying the technique to evaluate source-rock potential of the lower Kingak Shale. Geologic Background The Jurassic to Lower Cretaceous Kingak Shale contains both marine and terrigenous organic matter deposited in a marine siliciclastic setting influenced by pulses of syndepositional uplift of the Beaufort rift shoulder (also known as the Barrow arch; see figs. 3 and 4) during opening of the Canada Basin (Magoon and Claypool, 1984; Hubbard and others, 1987; Bird and Houseknecht, 2011). Houseknecht and Bird (2004) identified four depositional sequence sets in the Kingak Shale (fig. 3, K1–K4) that define a northern-sourced southward-offlapping succession of Beaufortian strata in the National Petroleum Reserve in Alaska (NPRA), and these sequence sets subsequently have been mapped eastward beyond the NPRA on the basis of seismic and well data. The basal K1 sequence set is 1,000 to more than 1,250 feet (ft) (300 to 380 meters [m]) thick across a broad area in the north-central NPRA that extends to the south as a lobe in the central NPRA (fig. 4). North of the zone of 2 Modified Method for Estimating Petroleum Source-Rock Potential Using Wireline Logs, With Application to the Kingak Shale

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