Insights into hydrocarbon reservoirs

Oil and natural gas are the dominant physical resources for modern society, having rapidly outstripped coal in the world’s economy.  Yet using them poses the threat of global climatic changes.  They are essentially a bank of solar energy, mediated by past photosynthesis into hydrocarbons; very long passed indeed.  Their burial tens and hundreds of million years ago helped modulate solar warming and drove up the level of oxygen in the atmosphere.  Using them reverses those aspects of the carbon cycle.  As the wars in Sudan, Afghanistan and Iraq demonstrate, developed economies will go to any lengths to retain access to known reserves.  Being so “hooked” on hydrocarbons, those economies have continually to find more.  However, the days of “trip-over” oilfields, such as those of Persian Gulf, are gone forever.  Exploration ventures into more and more difficult conditions, particularly offshore, where drilling is now going on in sea floor as deep as 2.5 km beneath the water surface.  Every aspect of the hydrocarbon industry poses increasing challenges; it seems to be at a crux.  For this reason, the 20 November 2003 issue of Nature includes a 56-page Insight supplement on a wide range of topics.  It starts with a review of the place of the petroleum industry in human history (Hall, C. et al. 2003.  Hydrocarbons and the evolution of human culture.  Nature, v. 426, p. 318-322).  Robert Berner of Yale University gives an up to date summary of the effects of fossil fuel use, in the context of the carbon cycle over geological time (Berner, R. 2003.  The long-term carbon cycle, fossil fuels and atmospheric composition. Nature, v. 426, p. 322-326).  The question, “How does petroleum form?” is addressed by Jeffrey Seewald of the Woods Hole Oceanographic Institute (Seewald, J.S. 2003.  Organic-inorganic interactions in petroleum-producing sedimentary basins. Nature, v. 426, p. 327-333).  The shift of exploration to ever deeper offshore areas brings it closer to the lines where continents split and drifted apart in the past.  So it isn’t surprising that Nature Insight includes a review by Cambridge University and BP geoscientists of how those margins evolved (White, N., Thompson, M. & Barwise, T. 2003.  Understanding the thermal evolution of deep-water continental margins. Nature, v. 426, p. 334-343).  Organisms other than humans exploit the energy locked in oil, and geochemists from the University of Newcastle upon Tyne address their role in actually degrading petroleum, so that many of the largest onshore petroleum reserves (oil sands in particular) pose great difficulties for exploitation (Head, I.M., Jones, D.M. & Larter, S.L. 2003.  Biological activity in the deep subsurface and the origin of heavy oil. Nature, v. 426, p. 344-352).  Methane generated by anaerobic bacteria in sea-floor sediments and in bogs can combine with water in the form of an ice-like substance called methane hydrate, if the pressure is high enough and temperature is close to 0ºC.  There is a lot of it about.  On the one hand it has huge economic potential, but on the other it poses awesome threats to the climate.  Several times in geological history vast amounts of methane have belched from the sea floor to drive up global temperature; it is a highly efficient “greenhouse” gas.  Dendy Sloane of the Colorado School of Mines addresses issues related to methane hydrates (Sloane, E.D. 2003.  Fundamental principles and applications of natural gas hydrates. Nature, v. 426, p. 353-359).  All these articles are deeply informative and well written.  They are “must-reads” for all geoscientists.  The sequence ends with a word from “management” (Shell International), in the form of a look ahead to how oil companies might clean up their act and become “friends of the Earth” (Stankiewicz, B.A. 2003.  Integration of geoscience and engineering in the oil industry – just a dream? Nature, v. 426, p. 360-363)

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