Screening, Evaluation, and Ranking of Oil Reservoirs Suitable for CO2-Flood EOR and Carbon Dioxide Sequestration
Authors: Shaw J. , Bachu S. 
Published: March 2010

Abstract
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.