Project Title: Experimental Study of Bitumen Generation and Its Role in Petroleum Generation
Mendenhall Fellow: Anna M. Cruse, acruse@usgs.gov
Duty Station: Denver, Colorado
Start Date: December 2, 2002
Education: M.S. (Geological Sciences), University of Missouri-Columbia, 1997; Ph.D. (Marine Geochemistry), MIT/WHOI Joint Program, 2002
Research Advisor: Michael D. Lewan, mlewan@usgs.gov
Project Description: Petroleum resources have a direct impact on the standard of living, economies, and security of the world's nations. A firm understanding of the physical and chemical variables that control petroleum formation is paramount to the development of predictive models used in assessment, exploration and recovery of such resources. However, despite the many advances in petroleum geochemistry to improve exploration efficiency and reservoir management in recent years, many key questions concerning petroleum generation, preservation and migration in the subsurface remain unanswered. This project seeks to address some of these questions by focusing on the role of bitumen in the generation of petroleum.The first step in petroleum formation is the diagenetic transformation of deposited sedimentary organic matter to kerogen, organic matter disseminated throughout the rock that is insoluble in non-oxidizing acids, bases and organic solvents. With burial and heating, kerogen decomposes to form bitumen, organic matter disseminated throughout a rock that is soluble in organic solvents. This bitumen then undergoes maturation to form petroleum that can be expelled from the rocks and subsequently recovered. However, despite the fact that the bitumen phase, rather than the original kerogen, is the ultimate source of petroleum, we remain ignorant of many aspects of bitumen's chemical composition and reaction kinetics. This is largely because bitumen formation has been assumed unimportant in commonly-utilized predictive models of petroleum formation. However, this assumption can lead to inaccuracies in the overall assessment of a petroleum system, ranging from the misidentification of the source rocks to overestimations of the thermal maturity of a particular rock unit. Another source of difficulty is that commonly used methods of measuring the kinetics of petroleum formation are conducted using apparatus that cannot distinguish between the kinetics of the transformation of kerogen to bitumen versus the transformation of bitumen to kerogen. This has lead to the assumption that petroleum generation in rocks occurs at relatively low activation energies, and that the formation of petroleum in nature must be catalyzed by mineral constituents.
In this project, bitumen formation from kerogen and the subsequent transformation of that bitumen to petroleum will be investigated using samples from the Devonian New Albany shale. Using both field and experimental techniques, variations in the chemical composition of the bitumen with respect to temperature and petroleum generation (i.e., yield curves) and the kinetics of bitumen generation will be established. The kinetic parameters derived from these experiments will shed light on the reaction mechanism of bitumen generation. Hypotheses generated from these results will be tested using simple model compounds, such as industrial polymers. A better understanding of the reaction mechanisms by which bitumen, and ultimately petroleum, form will provide the basis for improved extrapolations of laboratory results to natural environments, which is important not only for the assessment and management of our national reserves but is also key in predicting and minimizing the environmental impacts of resource development. Finally, the role of water as a solute within the bitumen itself will be investigated through a second series of experiments also utilizing the New Albany Shale. It has been hypothesized that water dissolved within bitumen serves to make oil immiscible within the bitumen, so that it can ultimately be expelled. The results from such experiments will help refine models of petroleum generation and accumulation that are key to assessing future resources and the discovery of new reserves.
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