Petroleum Generation, Extraction and Migration and Abiogenic Synthesis in Hydrothermal Systems

Abstract

Hydrothermal systems are associated with tectonic spreading centers and the organic matter alterations and secondary processes occurring there are rapid and efficient. In marine hydrothermal systems at water depths >1.5 km, the conditions driving chemical reactions are high temperatures (~60 to >400 °C), confining pressures (>150 bar), and other parameters such as pH, Eh and mineralogy in an aqueous open flow medium. Continental hydrothermal systems are also of interest as for example in active, failed or dormant rifts and in regions around piercement volcanoes and calderas. Organic matter alteration by reductive reactions to petroleum hydrocarbons proceeds generally from immature organic matter (also from entrained viable biota) instantaneously or over a brief geological time span (decades to millenia). The products are rapidly moved in fluids or as bulk phase from the regions at higher temperatures to areas at lower temperatures, where the higher molecular weight material accumulates. These conditions are conducive to organic chemistry which yields concurrent products primarily from reduction (due to mineral buffering), to a lesser extent from oxidation (high thermal stress) and traces from synthesis reactions. The behavior of organic matter (inclusive of methane to high molecular weight compounds >C40 and macromolecular organic matter, i.e. kerogen) in warm to supercritical water continues to be reported in new geographic locales, providing data for this novel geological phenomenon. Hydrothermal systems have also been proposed as possible sites for the origin of life on Earth. Because no modern-day terrestrial hydrothermal system is free from the influence of organic compounds derived from biologic processes, laboratory experiments provide the best opportunity for confirmation of the potential for organic synthesis in hydrothermal systems. Lipid compounds form easily by thermocatalytic synthesis from aqueous solutions of formic acid or oxalic acid which thermally disproportionate to H2, CO2, CO and H2O. Optimum synthesis occurs in stainless steel vessels by heating at 175–250 °C for 2 days and produces lipids ranging from C2 to >C35 which consist mainly of n-alkanols, n-alkanoic acids, n-alkyl formates, methyl alkanoates, n-alkanones, n-alkanes, n-alkenes and n-alkanals. Both reagent solutions yield the same lipid classes with essentially the same ranges of compounds.