Relative Permeability Characteristics for Supercritical CO2 Displacing Water in a Variety of Potential Sequestration Zones

Abstract

Abstract Sequestration in deep underground formations of large amounts of CO2, captured from large stationary sources, such as power plants, oil upgraders and refineries, is one method that is under consideration for reducing greenhouse gas emissions to the atmosphere in both Canada and United States. In hydrocarbon-producing regions, such as Texas in the United States and Alberta in Canada, CO2 geological sequestration is likely to first occur in depleted or abandoned oil and gas reservoirs. However, in many regions, including oil and gas producing areas, this is insufficient because either the sequestration capacity of oil and gas reservoirs is lower than the amount of CO2 emissions from large stationary sources, or because this capacity is not available until the reservoirs are depleted. Deep saline aquifers provide a very large capacity for CO2 sequestration that is immediately accessible, and they are found in all sedimentary basins in the North American mid-continent. Proper understanding of the relative-permeability character of such systems is essential in ascertaining CO2 injectivity and migration, and in assessing the suitability and safety of prospective CO2 sequestration sites. This paper reviews the experimental protocol and presents detailed water-CO2 relative permeability data for three sandstone and three carbonate formations in the Wabamun Lake area southwest of Edmonton in Alberta, western Canada, where four major coal-fired power plants which produce large volumes of CO2 are located. These formations are in general representative of the in-situ temperature, pressure, salinity, porosity and intercrystalline permeability characteristics of deep saline aquifers in on-shore North American sedimentary basins. The data will allow detailed numerical simulations of CO2 injection and sequestration processes both at this specific location, and for similar operations planned elsewhere and around the world. Introduction Human activity since the industrial revolution has had the effect of increasing atmospheric concentrations of greenhouse gases such as carbon dioxide (CO2) and methane (CH4)[1]. The high use of fossil fuels (more than 80% of the world's current energy consumption), is foreseen to continue well into this century[2,3], and is the major contributor to increased anthropogenic emissions of CO2. Thus, a major challenge in mitigating climate change effects is the reduction of CO2 emissions to the atmosphere. To meet mid- to long-term targets in reducing either CO2 emissions or their intensity, various mitigation approaches need to be considered, foremost among them being CO2 capture and sequestration (CCS), which will play an important role at least in the first half of this century if reduction targets are to be met3. In this context, CCS is the removal of CO2 directly from large anthropogenic sources and its injection and retention in geological media or in oceans for significant periods of time (centuries to millennia). Although the oceans represent possibly the largest potential CO2 sink, ocean sequestration involves issues of poorly understood physical and chemical processes, sequestration efficiency, cost, technical feasibility and environmental impact. In addition, ocean circulation and processes may bring to the fore legal, political and international limitations to this technology. Thus, CO2 sequestration in geological media appears to currently be the best available option for the long-term sequestration of CO2, and indeed this option is being actively pursued particularly in the United States[4], but also in Canada, northern Europe and Australia. Furthermore, for landlocked regions that are major energy and power producers, such as the Ohio Valley in the United States and Alberta in Canada, sequestration in geological media is the best and likely only option currently available for increasing CO2 sinks. By making possible the continued use of coal as a fuel for power generation, CCS is a technology that contributes to the stability and security of energy systems in North America and elsewhere, and provides a bridge from the current fossil-fuel based energy systems to a hydrogen-based economy envisaged for late this century[4].