EOR Screening Criteria Revisited—Part 2: Applications and Impact of Oil Prices
- J.J. Taber (New Mexico Petroleum Recovery Research Center) | F.D. Martin (New Mexico Petroleum Recovery Research Center) | R.S. Seright (New Mexico Petroleum Recovery Research Center)
- Document ID
- Society of Petroleum Engineers
- SPE Reservoir Engineering
- Publication Date
- August 1997
- Document Type
- Journal Paper
- 199 - 206
- 1997. Society of Petroleum Engineers
- 5.4.2 Gas Injection Methods, 5.4.10 Microbial Methods, 5.7.2 Recovery Factors, 6.5.3 Waste Management, 6.5.1 Air Emissions, 5.4.9 Miscible Methods, 5.5 Reservoir Simulation, 5.2.1 Phase Behavior and PVT Measurements, 4.2.3 Materials and Corrosion, 5.2 Reservoir Fluid Dynamics, 4.6 Natural Gas, 5.8.7 Carbonate Reservoir, 5.4.6 Thermal Methods, 2.5.2 Fracturing Materials (Fluids, Proppant), 4.2 Pipelines, Flowlines and Risers, 5.1 Reservoir Characterisation, 6.5.7 Climate Change, 5.4.7 Chemical Flooding Methods (e.g., Polymer, Solvent, Nitrogen, Immiscible CO2, Surfactant, Vapex), 4.1.2 Separation and Treating, 5.3.2 Multiphase Flow, 5.4.1 Waterflooding, 5.7.5 Economic Evaluations, 5.4 Enhanced Recovery, 2.4.3 Sand/Solids Control, 4.1.5 Processing Equipment
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Screening criteria are useful for cursory examination of many candidate reservoirs before expensive reservoir descriptions and economic evaluations are done. We have used our CO2 screening criteria to estimate the total quantity of CO2 that might be needed for the oil reservoirs of the world. If only depth and oil gravity are considered, it appears that about 80% of the world's reservoirs could qualify for some type of CO2 injection.
Because the decisions on future EOR projects are based more on economics than on screening criteria, future oil prices are important. Therefore, we examined the impact of oil prices on EOR activities by comparing the actual EOR oil production to that predicted by earlier NatI. Petroleum Council (NPC) reports. Although the lower prices since 1986 have reduced the number of EOR projects, the actual incremental production has been very close to that predicted for U.S. $20/bbl in the 1984 NPC report. Incremental oil production from CO2 flooding continues to increase, and now actually exceeds the predictions made for U.S. $20 oil in the NPC report, even though oil prices have been at approximately that level for some time.
Utilization of Screening Guides
With the reservoir management practices of today, engineers consider the various IOR/EOR options much earlier in the productive life of a field. For many fields, the decision is not whether, but when, to inject something. Obviously, economics always play the major role in "go/no-go" decisions for expensive injection projects, but a cursory examination with the technical criteria (Tables 1 through 7) is helpful to rule out the less-likely candidates. The criteria are also useful for surveys of a large number of fields to determine whether specific gases or liquids could be used for oil recovery if an injectant was available at a low cost. This application of the CO2 screening criteria is described in the next section.
Estimation of the Worldwide Quantity of CO2 That Could Be Used for Oil Recovery.
The miscible and immiscible screening criteria for CO2 flooding in Table 3 of this paper and in Table 3 of Ref. 1 were used to make a rough estimate of the total quantity of CO2 that would be needed to recover oil from qualified oil reservoirs throughout the world. The estimate was made for the IEA Greenhouse Gas R&D Program as part of their ongoing search for ways to store or dispose of very large amounts of CO2 in case that becomes necessary to avert global warming. The potential for either miscible or immiscible CO2 flooding for almost 1,000 oil fields was estimated by use of depth and oil-gravity data published in a recent survey.2 The percent of the fields in each country that met the criteria in Table 3 for either miscible or immiscible CO2 flooding was determined and combined with that country's oil reserves to estimate the incremental oil recovery and CO2 requirements. Assuming that one-half of the potential new miscible projects would be carried out as more-efficient enhanced secondary operations, an average recovery factor of 22% original oil in place (OOIP) was used, and 10% recovery was assumed for the immiscible projects. A CO2 utilization factor of 6 Mcf/incremental bbl was assumed for all estimates. This estimated oil recovery for each country was then totaled by region, and all the regions were totaled in Table 8 to provide the world totals.3 The basis for the assumed incremental oil recovery percentage and CO2 utilization factors and other details are given in Ref. 3.
Economics was not a part of this initial hypothetical estimate. Although pure CO2 can be obtained from power-plant flue gases (which contain only 9 to 12% CO2), the costs of separation and compression are much higher than the cost of CO2 in the Permian Basin of the U.S.3-5 For this study, we assumed that pure, supercritical CO2 was available (presumably by pipeline from power plants) for each of the fields and/or regions of the world. Table 8 shows that about 67 billion tons of CO2 would be required to produce 206 billion bbl of additional oil. The country-by-country results and other details (including separate sections on the costs of CO2 flooding) are given in Ref. 3. Although not much better than an educated guess with many qualifying numbers, our estimate agrees well with other estimates of the quantity of CO2 that could be stored (or disposed of) in oil reservoirs.3
Although this is a very large amount of CO2, when the CO2 demand is spread over the several decades that would be required for the hypothetical CO2 flooding projects, it would reduce worldwide power-plant CO2 emissions into the atmosphere by only a few percent per year. Therefore, more open-ended CO2 disposal methods (such as the more-costly deep-ocean disposal) will probably be needed if the complex general circulation models of the atmosphere ever prove conclusively that global warming from excess CO2 is under way.6,7 However, from the viewpoint of overall net cost, one of the most efficient CO2 disposal/storage systems would be the combined injection of CO2 into oil reservoirs and into any aquifers in the same or nearby fields.3,8 By including aquifers, this potential for underground CO2 storage would be increased significantly, and the quantity sequestered could have a significant impact on reducing the atmospheric CO2 emissions from the world's power plants.
Impact of Oil Prices on EOR
Major new EOR projects will be started only if they appear profitable. This depends on the perception of future oil price. Therefore, the relationship between future oil prices and EOR was a major thrust of the two NPC reports.9,10 These extensive studies used as much laboratory and field information as possible to predict the EOR production in the future for different ranges of oil prices. Now, it is possible to compare the NPC predictions with actual oil production to date. These comparisons were made recently to see how oil prices might affect oil recovery from future CO2 projects.3 We have extended these graphical comparisons and reproduced them here as Figs. 1 through 3. In general, the figures confirm that EOR production increases when prices increase and EOR production declines when prices fall, but not to the extent predicted. There is a time lag before the effect is noted. Figs. 1 and 2 show that total EOR production did increase in the early 1980's when oil prices were high. This was in response to an increase in the number of projects during this period when prices of up to U.S. $50/bbl or more were predicted. Although the rate of increase slowed in 1986 when oil prices dropped precipitously, EOR production did not decline until 1994, after several years of low oil prices (i.e., less than U.S. $20/bbl).11
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