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Advanced Biomarker and Diamondoid Correlations Identify Sources of Mixed and Altered Petroleum Charges in New Exploration Plays Across the Alaska North Slope


The Arctic Alaska petroleum province is geologically and geochemically complex. Mixed hydrocarbon charge from multiple source rocks and/or thermal maturity kitchens is common within an individual oil pool. To understand the history and quality of petroleum charge in new exploration plays and discoveries in Arctic Alaska, we are characterizing the geochemistry of North Slope petroleum systems using advanced molecular geochemical analyses of biomarkers and diamondoids. To date, three source-rock cores, as well as oil and condensate samples from 20 pools in 12 fields, 5 exploration well tests, and 3 seeps, have been analyzed. Results are especially timely for anticipating charge in stratigraphic traps in low-permeability sandstone reservoirs, where oil gravity and other chemical parameters are critical to economic viability.

The Amerada Hess Northstar 1 and Tenneco OCS YO338 Phoenix 1 cores provide baseline geochemical characterization of shaly and calcareous facies of the Triassic Shublik Formation, respectively, but the presence of migrated oil complicates interpretation of results from the Tenneco core. Bitumen extracted from USGS North Kalikpik 1 displays a distinct vertical change in organofacies reflecting gradation from the Lower Cretaceous pebble shale unit into the gamma-ray zone of the Hue Shale.

Building upon previously published geochemical correlation studies, we incorporate advanced biomarker and diamondoid correlative techniques (i.e., quantitative abundance and isotopic analysis of diamondoids) to delineate clastic and calcareous Shublik organofacies from source rocks located north and south of the Barrow Arch, characterize compositionally-altered oils, confirm petroleum charge mixing with both high- and low-maturity source contributions into many reservoirs, and distinguish sources of the mixed-provenance oils. In some cases, oils from multiple pools within a single field display relatively homogeneous geochemical profiles (i.e., Endicott Field), suggesting a common migration pathway. In other cases, significant variability exists among oils from multiple pools within a single field (i.e., Milne Point). Results also indicate that the significant new oil discovery in the Colville River Delta from the Cretaceous Nanushuk reservoir is primarily sourced from the calcareous Shublik. Our goal is to continue integrating these results with other subsurface data to interpret oil source to sink relationships, including likely migration pathways.