The current model for oil expulsion occurring at 120-150°C by anhydrous pyrolysis is not consistent with either analyses of the total organic carbon (TOC) content of subsurface source rocks or the chemical attributes of shallow oils. New data from North Sea Upper Jurassic source-rock samples show no decline in TOC between 120 and 150°C, which is a key prediction by the current model for oil expulsion. Instead, it is proposed here that oil expulsion occurs mainly at around 30°C at depths <1 km, similar to models advocated prior to 1970. Expulsion is suggested to be facilitated by CO2 gas generated from decomposing organic matter. Migration out of the source rock and into nearby high-permeable pathways occurs in the direction towards decreasing overburden via horizontal fractures that originate from swelling of load-bearing organic laminae. The thermally immature (heavy) oil is then converted to light oil within reservoirs by hydrogenation at 60-70°C. Hydrogen gas is common in subsurface fluids and is released by coalification of organic matter in mudstones in amounts sufficient to hydrogenate the reservoired heavy oil volumes. In this model, most heavy oil accumulations are interpreted as immature rather than the products of low-temperature biodegradation or partial evaporation of mature oil.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.