Experiments on the role of water in petroleum formation

https://doi.org/10.1016/S0016-7037(97)00176-2Get rights and content

Abstract

Pyrolysis experiments were conducted on immature petroleum source rocks under various conditions to evaluate the role of water in petroleum formation. At temperatures less than 330°C for 72 h, the thermal decomposition of kerogen to bitumen was not significantly affected by the presence or absence of liquid water in contact with heated gravel-sized source rock. However, at 330 and 350°C for 72 h, the thermal decomposition of generated bitumen was significantly affected by the presence or absence of liquid water. Carbon-carbon bond cross linking resulting in the formation of an insoluble bitumen (i.e., pyrobitumen) is the dominant reaction pathway in the absence of liquid water. Conversely, thermal cracking of carbon-carbon bonds resulting in the generation of saturate-enriched oil, which is similar to natural crude oils, is the dominant reaction pathway in the presence of liquid water. This difference in reaction pathways is explained by the availability of an exogenous source of hydrogen, which reduces the rate of thermal decomposition, promotes thermal cracking, and inhibits carbon-carbon bond cross linking. The distribution of generated n-alkanes is characteristic of a free radical mechanism, with a broad carbon-number distribution (i.e., C5 to C35) and only minor branched alkanes from known biological precursors (i.e., pristane and phytane). The generation of excess oxygen in the form of CO2 in hydrous experiments and the high degree of hydrocarbon deuteration in a D2O experiment indicate that water dissolved in the bitumen is an exogenous source of hydrogen. The lack of an effect on product composition and yield with an increase in H+ activity by five orders of magnitude in a hydrous experiment indicates that an ionic mechanism for water interactions with thermally decomposing bitumen is not likely. Several mechanistically simple and thermodynamically favorable reactions that are consistent with the available experimental data are envisaged for the generation of exogenous hydrogen and excess oxygen as CO2. One reaction series involves water oxidizing existing carbonyl groups to form hydrogen and car☐yl groups, with the latter forming CO2 by decar☐ylation with increasing thermal stress. Another reaction series involves either hydrogen or oxygen in dissolved water molecules directly interacting with unpaired electrons to form a hydrogen-terminated free-radical site or an oxygenated functional group, respectively. The latter is expected to be susceptible to oxidation by other dissolved water molecules to generate additional hydrogen and CO2. In addition to water acting as an exogenous source of hydrogen, it is also essential to the generation of an expelled saturate-enriched oil that is similar to natural crude oil. This role of water is demonstrated by the lack of an expelled oil in an experiment where a liquid Gasingle bondIn alloy is substituted for liquid water. Experiments conducted with high salinity water and high water/rock ratios indicate that selective aqueous solubility of hydrocarbons is not responsible for the expelled oil generated in hydrous pyrolysis experiments. Similarly, a hydrous pyrolysis experiment conducted with isolated kerogen indicates that expelled oil in hydrous pyrolysis is not the result of preferential sorption of polar organic components by the mineral matrix of a source rock. It is envisaged that dissolved water in the bitumen network of a source rock causes an immiscible saturate-enriched oil to become immiscible with the thermally decomposing polar-enriched bitumen. The overall geochemical implication of these results is that it is essential to consider the role of water in experimental studies designed to understand natural rates of petroleum generation, expulsion mechanisms of primary migration, thermal stability of crude oil, reaction kinetics of biomarker transformations, and thermal maturity indicators in sedimentary basins.

References (163)

  • EspitalieJ. et al.

    Role of mineral matrix during kerogen pyrolysis

    Org. Geochem.

    (1984)
  • HelgesonH.C. et al.

    Petroleum, oil field waters, and authigenic mineral assemblages: Are they in metastable equilibrium in hydrocarbon reservoirs?

    Geochim. Cosmochim. Acta

    (1993)
  • HersheyJ.P. et al.

    The pK*, for the dissociation of H2S in various ionic media

    Geochim. Cosmochim. Acta

    (1988)
  • HoeringT.C.

    Thermal reactions of kerogen with added water, heavy water and pure organic substances

    Org. Geochem.

    (1984)
  • HorsfieldB. et al.

    The influence of minerals on the pyrolysis of kerogens

    Geochim. Cosmochim. Acta

    (1980)
  • HuizingaB.J. et al.

    The role of minerals in the thermal alteration of organic matter—III. Generation of bitumen in laboratory experiments

    Org. Geochem.

    (1987)
  • JandacekR.J. et al.

    Effect of an aqueous phase on the solubility of cholesterol in an oil phase

    J. Lipid Res.

    (1977)
  • KuangzongQ. et al.

    Chemical structure and hydrocarbon formation of the Huanxian brown coal, China

    Org. Geochem.

    (1994)
  • KuoLung-Chuan et al.

    A multicomponent oil-cracking kinetics model for modeling preservation and composition of reservoir oils

    Org. Geochem.

    (1994)
  • LewanM.D.

    Effects of thermal maturation on stable organic carbon isotopes as determined by hydrous pyrolysis of Woodford Shale

    Geochim. Cosmochim. Acta

    (1983)
  • LewanM.D.

    Stable carbon isotopes of amorphous kerogens from Phanerozoic sedimentary rocks

    Geochim. Cosmochim. Acta

    (1986)
  • LewanM.D. et al.

    Irradiation of organic matter by uranium decay in the Alum Shale, Sweden

    Geochim. Cosmochim. Acta

    (1989)
  • LewanM.D. et al.

    Effects of thermal maturation on steroid hydrocarbons as determined by hydrous pyrolysis of phosphoria retort shale

    Geochim. Cosmochim. Acta

    (1986)
  • LewanM.D. et al.

    Gamma60Co-irrediation of organic matter in the Phosphoria Retort Shale

    Geochim. Cosmochim. Acta

    (1991)
  • LundegardP.D. et al.

    Hydrous pyrolysis: A tool for the study of organic acid synthesis

    Appl. Geochem.

    (1987)
  • ArcaM. et al.

    Thermal stability of poly(pyrrole)

    J. Mater. Sci. Lett.

    (1987)
  • BarthT. et al.

    Volatile organic acids produced during kerogen maturation-amounts, composition and role in migration of oil

    Org. Geochem.

    (1987)
  • BaskinD.K. et al.

    Early generation characteristics of a sulfur-rich Monterey kerogen

    Amer. Assoc. Petrol. Geol. Bull.

    (1992)
  • BensonS.W.

    Thermochemical Kinetics

    (1976)
  • BockrathB.C. et al.

    Solvent swelling of liquefaction residues

    Energy & Fuels

    (1987)
  • BolesJ.R. et al.

    Diagenetic carbonate in Miocene sandstone reservoir, San Joaquin Basin, California

    AAPG Bull.

    (1987)
  • BradyC.J. et al.

    Water-hydrocarbon liquid-liquid-vapor equilibrium measurements to 500°F

    Gas Processors Association Res. Rept. 62

    (1982)
  • BraunR.L. et al.

    Pyrolysis kinetics for lacustrine and marine source rocks by programmed micropyrolysis

    Energy & Fuels

    (1991)
  • de la BretequeP.

    Gallium and gallium compounds

  • BrooksB.T.

    Evidence of catalytic action in petroleum formation

    Indust. Eng. Chem.

    (1952)
  • BuchardtB. et al.

    Reflectance of vitrinite-like macerals as a thermal maturity index for Cambrian-Ordovician Alum Shale, southern Scandinavia

    Amer. Assoc. Petrol. Geol. Bull.

    (1990)
  • ButlerJ.N.

    Carbon Dioxide Equilibria and their Applications

    (1982)
  • CampbellJ.H. et al.

    Oil shale retorting: Effects of partical size and heating rate on oil evolution and intrapartical oil degradation

    In Situ

    (1978)
  • CarrollJ.J. et al.

    Phase equilibrium in the system water-hydrogen sulfide: Modelling the phase behavior with an equation of state

    Canadian J. Chem. Eng.

    (1989)
  • ChapiroA.

    Radiation Chemistry of Polymeric Systems

    (1962)
  • CharlesbyA.

    The cross-linking and degradation of paraffin chains by high-energy radiation

  • CharlesbyA.

    Atomic Radiation and Polymers

    (1960)
  • CliffordC.W.

    The solubility of water in gasoline and in certain other organic liquids, determined by the calcium chloride method

    J. Ind. Eng. Chem.

    (1921)
  • CoburnT.T. et al.

    Water generation during pyrolysis of oil shales. 1. Sources

    Energy & Fuels

    (1989)
  • CombazA. et al.

    Organic sedimentation and genesis of petroleum in Mahakam delta, Borneo

    Amer. Assoc. Petrol. Geol. Bull.

    (1978)
  • ComleyE.A. et al.

    Catalytic processes for hydrogen manufacturing

    Sixth World Petrol. Congr.

    (1963)
  • ConnanJ.

    Time-temperature relation in oil genesis

    Amer. Assoc. Petrol. Geol. Bull.

    (1974)
  • CoolesG.P. et al.

    Calculation of petroleum masses generated and expelled from source rocks

    Org. Geochem.

    (1986)
  • CoolesG.P. et al.

    Non-hydrocarbons of significance in petroleum exploration: Volatile fatty acids and non-hydrocarbon gases

    Mineral. Mag.

    (1987)
  • CumminsJ.J. et al.

    Thermal degradation of Green River kerogen at 150° to 350°C

    U.S. Bureau of Mines, Investigation Report 7620

    (1972)
  • Cited by (0)

    View full text