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Evidence for Hydrocarbon Generation from NSOs: Implication for Modeling of Oil and Gas Generation in Basins

Patrick G. Hatcher¹, Françoise Behar², Albert Kamga¹, and Elodie Salmon¹
¹Old Dominion University, Norfolk, Virginia
²TOTAL, Paris, La Defense, France

Understanding the occurrence and generation of gaseous and liquid hydrocarbons in sedimentary basins is often predicated on knowing the processes involved in cracking and expulsion of these hydrocarbons from the kerogen matrix. There are several theories on how cracking of the kerogen occurs to yield hydrocarbons; however, there is little definitive evidence for any of these that is based on a full molecular-level understanding of the proposed pathways. A major theory considers that oil and gas is generated directly by cracking of the kerogen in a series of parallel reactions. Another suggests that successive reactions acting on the main kerogen polymer involve the generation of hydrocarbons by cracking of both the kerogen and the intermediate sub-products. In the successive reaction kinetic scheme presumably, compounds of intermediate molecular weight (NSOs) are formed first from the kerogen and then become the main source of petroleum. Resolving which of these transformation pathways is most important is crucial to our ability to model and predict petroleum formation in sedimentary basins.

To evaluate the feasibility of each of these pathways the present study presents some new molecular-level correlations among NSO fractions and extracted oils from immature kerogen subjected to artificial maturation in sealed gold tubes. A Type I kerogen from the Green River formation was pyrolyzed in a closed system at various temperature/time conditions. The NSO compounds generated during the artificial maturation were collected by successive n-pentane and dichloromethane (DCM) extractions and analyzed using a new ultrahigh resolution mass spectrometric technique involving electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICR-MS) to identify dominant series of compounds. This approach allows us to examine the individual elemental components of polar NSOs by providing ultra-resolution mass spectra whose precise mass assignments provide the requisite information from which elemental compositions are determined.

AAPG Search and Discovery Article #120098©2013 AAPG Hedberg Conference Petroleum Systems: Modeling the Past, Planning the Future, Nice, France, October 1-5, 2012