CLIMATE CHANGE AND SEQUESTRATION OF CO2 INGEOLOGICAL MEDIA: A VIABLE OPTION FOR THEENERGY INDUSTRY

摘要

Atmospheric concentrations ofCO2, a major greenhouse gas, have risenprimarily as a consequence of fossil fuelcombustion for energy production. Thedeveloped world has committed to reduceby 2012 the release into the atmosphere ofanthropogenic CO2 at levels on averagelower by 5.2% than those of 1990.Mitigation of human-induced climatechange involves basically threeapproaches. The first approach is toincrease the efficiency of primary energyconversion and end use. The secondapproach is to substitute lower-carbon orcarbon-free energy sources for the currentsources. The third approach is carbonsequestration. Any viable system forsequestering carbon must be safe,environmentally benign, effective,economical and acceptable to the public.Sequestration of CO2 in geological mediais likely to provide the first large-scaleopportunity for concentrated sequestrationof CO2, being immediately applicable as aresult of the experience already gained inoil and gas production, and storage ofnatural gas.Given their inherent advantages,such as availability, competitive cost, andease of transport and storage, fossil fuelswill remain a major component of world’senergy supply in the foreseeable future.Fossil fuels are serendipitously linked withsedimentary basins in which CO2 can besequestered1. CO2 can be sequestered instructural or stratigraphic traps, similarlyto hydrocarbons trapped in naturalreservoirs. Depleted gas reservoirs areprimary candidates as geological traps forCO2. Carbon dioxide can be trapped bydissolution in oil or in deep brines.Solubility trapping in oil still requires ageological trap (the oil reservoir). The technology is commercially proven andapplied in enhanced oil recoveryoperations. Up to 30 % of CO2 injected indeep saline aquifers dissolves over time inthe formation water2. Injection anddissolution of CO2 in regional-scale flowsystems leads to hydrodynamic trappingbeneath competent, regional-scale sealingaquitards3. A considerable increase inpermanently sequestered CO2 by injectionin deep aquifers would be achievedthrough mineral trapping3. Preferentialadsorption of gaseous CO2 into the coalmatrix and methane release leads toadsorption trapping in coal beds4. Injectionof CO2 into deep uneconomic coal bedshas the added advantage that it releasesmethane that can be produced in enhancedcoalbed methane recovery4. Cavitytrapping refers to CO2 injection in minedcaverns in salt beds and domes, similarlyto the storage of natural gas. Although saltcaverns theoretically have a large storagecapacity, the associated costs are too highand the environmental problems related tobrine disposal are significant.The selection of the method, strataand site for CO2 sequestration ingeological media depends on a number ofspecific criteria being met. These criteriaare scale dependent, some applying at thebasin scale, other being site specific. Thebasin-scale criteria5 relate to: 1) tectonicsetting, b) hydrodynamic and geothermalregimes, c) hydrocarbon potential andbasin maturity; d) surface infrastructure;and e) socio-political conditions in thejurisdiction covering the basin. The sitespecificcriteria fall into several categories:1) surface; 2) in-situ conditions; 3) storagecapacity; 4) injectivity and flow dynamics;and 5) sequestration efficiency(confinement safety). The surfaceinfrastructure for CO2 separation, capture,transport and injection into the ground,