Geological sequestration of CO2 in the subsurface: lessons from CO2 injection enhanced oil recovery projects in oilfields
Richard H. Worden, Leta K. Smith, 2004. "Geological sequestration of CO2 in the subsurface: lessons from CO2 injection enhanced oil recovery projects in oilfields", Geological Storage of Carbon Dioxide, Shelagh J. Baines, Richard H. Worden
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In this paper production geochemical data from oil fields where CO2 has been injected to enhance oil recovery (CO2-EOR) and experimental simulations of this process are reviewed. These data show that over the timescale of days to many years, CO2 injected into the subsurface typically results in the bulk dissolution of carbonate minerals. There is little evidence for the sequestration of the injected greenhouse gas as a solid phase carbonate mineral on the timescale of the CO2-EOR projects or experiments. There is extensive aqueous geochemical, petrographic and core analysis evidence that supports the conclusion that CO2, injected into oil fields to enhance secondary recovery, leads to the bulk dissolution of calcite, dolomite and siderite. Although carbonate dissolution leads to enhanced porosity, the expected commensurate increase in permeability may be offset by the migration of clays, liberated by the action of the acidic water on the rock, with consequent blocking of pore throats. Additionally, injection of CO2 into oil fields can result in asphaltene deposition on mineral surfaces. Such a bitumen coat could ultimately isolate the mineral matrix from injected fluids and insulate the rock to the injected greenhouse gas. Localized precipitation of calcite scale has been reported in the topside facilities of CO2-EOR projects and in the low-pressure region of experimental simulations.
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Carbon dioxide (CO2) is the main compound identified as affecting the stability of the Earth’s climate. A significant reduction in the volume of greenhouse gas emissions to the atmosphere is a key mechanism for mitigating climate change. Geological storage of CO2, or the injection and long-term stabilization of large volumes of CO2 in the subsurface in saline aquifers, in existing hydrocarbon reservoirs or in unmineable coal seams, is one of the more technologically advanced options available. A number of studies have been carried out and are reported here. They are aimed at understanding the safety, physical and chemical behaviour and long-term fate of CO2 when stored in geological formations. Until efficient, alternative energy options can be developed, geological storage of CO2, the subject of this volume, provides a mechanism to reduce carbon emissions significantly whilst continuing to meet the global demand for energy.