Geological sequestration of CO2 in EOR operations has been recognized as one of the more viable means of reducing emissions of anthropogenic CO2 into the atmosphere in response to global climate change. This option, which lowers the cost of CO2 sequestration by recovering incremental oil, is particularly attractive in mature sedimentary basins, such as the Western Canada Sedimentary Basin where many oil pools are near depletion, and where most of the needed infrastructure is already in place. A method was developed for the rapid screening and ranking of oil reservoirs suited for CO2-flood EOR, which is particularly fit for a very large number of reservoirs as listed in eserves databases, and which does not require detailed reservoir engineering analysis. Oil reservoirs are screened on the basis of oil gravity, reservoir temperature and pressure, minimum miscibility pressure and remaining oil saturation, to determine their suitability for CO2 flooding, and an analytical method is used to calculate the incremental oil recovery at breakthrough and for any hydrocarbon pore volume (HCPV) fraction of injected CO2. In addition, the reservoir capacity for CO2 sequestration is calculated. eservoirs are ranked according to a set of criteria with corresponding assigned weights to identify and select the best-suited reservoirs for CO2 flooding and sequestration. The method was applied to 8,637 oil reservoirs listed in the 2000 Alberta reserves database. Of these, 4,470 passed the screening criteria and were ranked based on technical and performance characteristics. Preliminary calculations predict that 150 × 106, 422 × 106, or 558 × 106 m3, of additional oil could be produced from Alberta's reservoirs at breakthrough, and at 50% and 100% HCPVof injected CO2, respectively; meanwhile sequestering 127, 591 and 1,118 Mt CO2, respectively. Thus, geological sequestration of CO2 in Alberta oil reservoirs suitable for CO2 flooding could provide a means for significantly reducing anthropogenic CO2 emissions from major point sources while, at the same time, realizing an economic benefit. Introduction As a result of anthropogenic CO2 emissions, atmospheric concentrations of CO2 have risen significantly from pre-industrial levels, primarily as a consequence of fossil-fuel combustion for energy production. Circumstantial evidence suggests that the increase in greenhouse-gas concentrations in the atmosphere leads to climate warming and weather changes(1). In response to the need to avoid irreversible climate changes and the associated risks resulting from greenhouse effects, most of the developed world, including Canada, has committed to reduce by 2012 the release into the atmosphere of anthropogenic CO2 to levels below those of 1990. However, although the intensity of CO2 emissions has markedly decreased, Canada's emissions have increased steadily since 1990 as a result of economic development. Given the inherent advantages, such as large resources, availability, ease of transport and storage, and competitive cost, fossil fuels, which currently provide about 75% of the world's energy, will likely remain as a major component of the world's energy supply for at least this century(1, 2). In light of this, producing regions, such as Western Canada, need to find ways to both increase oil production and reduce CO2 emissions.

A complete understanding of the various rock properties is essential in determining the rockfluid interactions that take place during coreflood experiments. Although Berea sandstone, Baker dolomite and Indiana limestone have been used by the petroleum industry as reference materials, very few data have been reported in the literature regarding their basic rock properties. This paper contains petrographic and petrophysical data for these rock types. Twelve representative samples were selected to study the variability and the relationship of several rock properties, including mineral content, grain and pore size, porosity, permeability, specific surface area, mercury capillary pressure, and electrokinetic properties. The results indicate: 1) the Upper Berea sandstone samples studied exhibit correlations between porosity, permeability, specific surface area, and various parameters obtained from the mercury capillary pressure analyses that may be used to predict certain rock properties, 2) Baker dolomite and Indiana limestone contain a small amount of clays and organic matter, 3) These carbonates show a bimodal pore throat size distribution based on mercury capillary pressure analyses, and 4) The surface charges of these rocks are very dependent on the brine composition and pH. The specific surface area and surface charge data can be used to determine the amount of chemical retention during corefloods using these or similar reservoir rocks. This information is necessary to optimize chemical processes used in the oilfield.

We have used a sintered glass bead core to simulate the spaces and surfaces of reservoir rock in studies of the bacterial plugging phenomenon that affects waterflood oil recovery operations. The passage of pure or mixed natural populations of bacteria through this solid matrix was initially seen to promote the formation of adherent bacterial microcolonies on available surfaces. Bacteria within these microcolonies produced huge amounts of exopolysaccharides and coalesced to form a confluent plugging bioffim that eventually caused a >99% decrease in core permeability. Aerobic bacteria developed a plugging biofilm on the inlet face of the core, facultative anaerobes plugged throughout the core, and dead bacteria did not effectively plug the narrow (33-,um) spaces of this solid matrix because they neither adhered extensively to surfaces nor produced the extensive exopolysaccharides characteristic of living cells. The presence of particles in the water used in these experiments rapidly decreased the core permeability because they became trapped in the developing biofilm and accelerated the plugging of pore spaces. Once established, cells within the bacterial biofilm could be killed by treatment with a biocide (isothiazalone), but their essentially inert carbohydrate biofilm matrix persisted and continued to plug the pore spaces, whereas treatment with 5% sodium hypochlorite killed the bacteria, dissolved the exopolysaccharide biofilm matrix, and restored permeability to these plugged glass bead cores. * Corresponding author. were both replicable and approximately equal to those of an "open" sandstone. Thus, especially in our early studies in which pure cultures of aquatic bacteria were used, any changes in permeability that occurred in the model cores could be attributed fully to microbiological factors.

Geological sequestration of CO2 is an immediately available means of reducing CO2 emissions into the atmosphere from major point sources, such as thermal power plants and the petrochemical industry, and is particularly suited to landlocked Alberta. Trapping CO2 in depleted hydrocarbon reservoirs and through enhanced oil recovery (EOR) will likely be implemented first because the geological conditions are already well known and the infrastructure is partially in place. Assuming that the volume occupied by the produced oil and gas can be backfilled with CO2, the ultimate theoretical CO2 sequestration capacity in Alberta's gas reservoirs not associated with oil pools is estimated to be 11.35 Gt. The sequestration capacity in the gas cap of oil reservoirs is 865 Mt of CO2, but this additional capacity will become available sometime in the more distant future after both the oil and gas have been produced from these reservoirs. The theoretical ultimate sequestration capacity at depletion in oil pools in single drive and primary production is only 615 Mt of CO2. Depending on the strength of the underlying aquifer, water invasion has the effect of reducing the theoretical CO2 sequestration capacity of depleted reservoirs by 60% on average for oil pools and 28% on average for gas pools, if the reservoir is only allowed to be repressurized back to its initial pressure. Weak aquifers have no effect on reservoir CO2 sequestration capacity. If other factors are taken into account, such as reservoir heterogeneity and CO2 mobility and buoyancy, then the effective ultimate CO2 sequestration capacity at depletion in hydrocarbon reservoirs in Alberta is estimated to be 9,860 Mt for nonassociated gas pools and 242 Mt for oil reservoirs currently in single drive and primary production. However, most reservoirs have a relatively small CO2 sequestration capacity, rendering them largely uneconomic. In addition, shallow reservoirs are inefficient because of low CO2 density, while very deep reservoirs may be too costly because of the high cost of CO2 compression, and also inefficient in terms of the net CO2 sequestered. If only the largest reservoirs in the depth range of approximately 900 m to 3,500 m are considered, each with an ndividual capacity greater than 1 Mt CO2, then the number of reservoirs in Alberta suitable for CO2 sequestration in the shortto- medium term drops to 565 non-associated gas reservoirs and 22 oil reservoirs in single drive or primary production, with a practical CO2 sequestration capacity of 2,660 and 115 Mt of CO2, respectively. This practical capacity of Alberta's oil and gas reservoirs for CO2 sequestration may provide a sink for CO2 captured from major point sources that is estimated to last for a few decades. Introduction As a result of anthropogenic CO2 emissions, atmospheric concentrations of CO2, a greenhouse gas, have risen from pre-industrial levels of 280 ppm to the current level of more than 360 ppm, primarily as a consequence of fossil-fuel combustion for energy production. This has led to climate warming and weather changes.

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractAtmospheric concentrations of CO 2 have risen since the beginning of the industrial revolution, primarily as a consequence of fossil fuel combustion for energy production and other industrial activities. Recognizing the challenge imposed by the potential for climate change, recent initiatives by various governments and by energy producers target a significant reduction in the intensity of CO 2 emissions into the atmosphere. A major mitigation strategy for reducing the intensity and amount of CO 2 emissions into the atmosphere is CO 2 capture and sequestration, of which geological sequestration is a major component. Although enhanced oil recovery operations have the lowest capacity of all options for geological CO 2 sequestration, they are most likely to be implemented first because of the additional economic benefit that will help offset the cost of CO 2 sequestration.Assuming that the pore space previously occupied by the produced oil can be backfilled with CO 2 , a methodology has been developed for the identification and screening of oil reservoirs that are suitable for CO 2 flooding and for estimating their CO 2 sequestration capacity at depletion, as well as under enhanced oil recovery.