Assessment of Oil and Gas In Place In Source-Rock Systems of Arctic Alaska

Stefan Ladage

A probabilistic, geology-based methodology developed by the German Federal Institute for Geosciences and Naturla Resources (BGR) and geological data and interpretations developed by the Geological Survey (USGS), are being integrated to estimate the volumes of oil and gas in place in source-rock systems of Arctic Alaska. Three significant source rocks are known to have generated the large volumes of oil and gas that have been found in conventional accumulations on the North Slope: the Triassic Shublik Formation, the lower part of the Jurassic–Lower Cretaceous Kingak Shale, and the Cretaceous pebble shale unit and Hue Shale (“Brookian shale”). Depending upon their kerogen content, lithology and thermal maturity these three source rocks are inferred to have significant but differing potential for development of unconventional accumulations of oil, natural gas liquids, and gas in various places on the North Slope. Each of the source rock systems is known to have generated geochemically identifiable hydrocarbon volumes. These geologically and geochemically distinct source rocks occur at depths ranging from less than 1,000 meters along the northern coast to more than 6,000 meters in the Brooks Range foothills. Accordingly, their thermal maturity grades from the onset of oil generation in the north, through the oil window, and well into the dry gas window in the south. On the basis of these geological considerations, six assessment units were defined for evaluation of in-place hydrocarbons. Following geological screening and risking for thickness, total organic carbon, kerogen type, and thermal maturity, input distributions are developed for various physical parameters such as potentially productive area, formation thickness, effective porosity, water, oil and gas saturation, pressure, temperature, gas expansion, and gas adsorption. These input distributions are then combined in Monte Carlo-type simulations that yield probabilistic estimates of oil, free gas, adsorbed gas, and natural gas liquids. Probabilistic estimates are being developed for each of the USGS-defined assessment units on the North Slope. By comparing BGR/USGS simulations of in-place hydrocarbon volumes with USGS performance-based assessments of technically recoverable oil, gas and natural gas liquids in the same assessment units, improved understanding of the potential for unconventional oil and gas resources is achieved for source rock systems of northern Alaska.

AAPG Search and Discovery Article #90177©3P Arctic, Polar Petroleum Potential Conference & Exhibition, Stavanger, Norway, October 15-18, 2013