Life-Cycle Analysis of CO2 EOR on EOR and Geological Storage

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Ind. Eng. Chem. Res. 2006, 45, 2483-2488

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Life-Cycle Analysis of CO2 EOR on EOR and Geological Storage through Economic Optimization and Sensitivity Analysis Using the Weyburn Unit as a Case Study† Jitsopa Suebsiri,*,‡ Malcolm Wilson,§ and Paitoon Tontiwachwuthikul§ EnVironmental System Engineering and International Test Centre for CO2 Capture, UniVersity of Regina, Regina, Saskatchewan, Canada S4S 0A2

At the global, national, and subnational levels, many policies have been created or are in the process of development to deal with greenhouse gas (GHG) emissions, particularly CO2. CO2 enhanced oil recovery (EOR) is an option available to governments and industry to help meet emission reduction levels. In addition to increasing the production of oil, the CO2 can be stored in the oil reservoir for a very long period of time. However, CO2 capture and CO2 EOR operation result in significant costs and energy penalties, for example, CO2 capture from a point source, transportation to the site of use, and recycling produced CO2. This article evaluates the life cycle of CO2 storage from delivery to the oil field through the production, transportation, and refining of the oil and identifies opportunities for optimization. Information from the IEA GHG Weyburn Monitoring and Storage Project is used to provide baseline information for the storage of CO2. The value of this life-cycle study lies in the development of an understanding of the “carbon” economics of the EOR process and the impact on net storage of changes to the value of different components in the chain. These results provide a mechanism whereby environmental consequences can be evaluated within economic decisionmaking. Introduction Greenhouse gases (GHGs), particularly carbon dioxide (CO2), have been extensively studied as a result of concerns about global climate change. In 1997, an agreement among 84 countries, the Kyoto Protocol, was approved with a goal of achieving major greenhouse gas emissions reductions. Now in force, the Kyoto Protocol has legal standing to back its goal of emissions reductions, unlike its predecessor, the United Nations Framework Convention on Climate Change (signed in 1992 and entered into force in 1994), which only provided guidelines for countries’ emissions reductions. CO2 emission reductions can be accomplished through the application of energy efficiency and conservation, fuel switching, renewable energy, and capture and storage. The capture and storage of carbon is one of the approaches for CO2 emission reduction being given serious consideration globally. The CO2 must be captured from large industrial sources as a relatively pure gas before it can be stored. The rationale for this is two-fold. In the first place, certain contaminants can negatively impact the effects of CO2 in enhanced oil recovery. (If this is the chosen storage mechanism, in saline aquifer storage, the purity concerns are less marked.) Second, the costs of compression can rise significantly if the levels of contaminants are high; as an example, the cost of compressing an untreated flue gas for injection into the subsurface would be prohibitively high and would, in any event, waste what might turn out to be limited pore space in the subsurface. CO2 for enhanced oil recovery (EOR) is a relatively mature process that has been commercially applied on an increasingly large scale in several petroleum basins during the past three decades. The advantages are not only using CO2 to enhance oil recovery, but * To whom correspondence should be addressed. E-mail: [email protected]. Tel.: (306) 596-4924. Fax: (306) 337-2301. † This paper is an expanded version of work presented at the 7th International Conference on Greenhouse Gas Control Technologies, Vancouver, Canada, Sep 2004. ‡ Environmental System Engineering. § International Test Centre for CO2 Capture.

also storing CO2 for the long term. Unfortunately, CO2 enhanced oil recovery cannot be effectively applied to all types of reservoirs. Crude oils with a specific gravity less than 0.9218 (greater than 22° API) are best suited to enhanced oil recovery with CO2.1 Additionally, depths should ideally be such that miscible flooding can occur to optimize recovery efficiency. In the case of a facility using fossil fuel, it is possible to remove the CO2 before it is released into the atmosphere. The CO2 would then be stored through EOR or injection into deep saline aquifers. The Weyburn oil field is investigated as an illustrative case in this study because of the public availability of large amounts of data resulting from an extensive four-year research project completed in 2004. This article focuses on applying life-cycle analysis (LCA) of CO2 storage from delivery to the oil field through the production, transportation, and refining of the oil and identifies opportunities for optimization. The Weyburn unit has proven to be an exceptional natural laboratory for the study of CO2 storage, based in part on the extensive historical field production and well data available, combined with the baseline data collected prior to the first CO2 injection, the abundant core material, and the accessibility of the site.2 The Weyburn unit, located 130 km southeast of Regina, Saskatchewan, Canada, as shown in Figure 1, is operated by EnCana Corporation on behalf of a large number of unit holders. The Weyburn reservoir produces crude oil, which has a specific gravity in the range of 0.850-0.9041 (25°-34° API), from the Mississippian Midale Beds of the Charles Formation that occur at a depth of around 1450 m. The original reservoir temperature (near 65 °C) and original pressures (around 14.5 MPa) indicate that CO2 in the pool likely exists as a supercritical fluid. (The temperature and pressure are above the critical point of approximately 31 °C and 7 MPa.) In summary, the geological setting of the Weyburn oil pool is considered highly suitable for CO2based EOR and long-term storage of CO2. The injected CO2 has the potential to remain for a similar time scale as the hydrocarbons in the reservoir, which have been trapped for geological time scales.

10.1021/ie050909w CCC: $33.50 © 2006 American Chemical Society Published on Web 12/09/2005

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Figure 1. Location of the Weyburn unit.

Figure 2. Basic elements of the fossil-energy chain.

Life-Cycle Analysis of CO2 EOR Life-cycle analysis is a tool to assist in understanding the total impact and cost that a product has on the environment. This means assessing the total life cycle of a product, process, or activity from the mining of raw materials used in its

production and distribution through use, ultimate reuse or recycling, and eventual disposal. In this study, the focus is on the life-cycle analysis of CO2 EOR at the Weyburn unit based on a predicted project lifetime of approximately 25 years. The study includes the identification and quantification of energy requirements and related CO2 emissions, as well as CO2 storage. The basic cycle of CO2 in EOR contains the primary elements of the fossil-energy chain, which includes the source of the CO2, the oil field, the oil consumers, and the atmosphere. Figure 2 illustrates the cycle of CO2 in EOR. The cycle of CO2 EOR starts at a CO2 source in which CO2 is captured from fossilfuel combustion rather than being released into the atmosphere. The Dakota Gasification Company (DGC) serves as the CO2 source. The CO2 from an exhaust stream is captured and compressed to increase the pressure to greater than 15 MPa. DGC will deliver approximately 20 million tonnes of CO2 over a 15year period via a 325-km pipeline to the Weyburn unit. This CO2, approximately 96% pure, is assumed to be the total CO2 supply at the oil field. (There is some suggestion that the volumes purchased might be greater in the future, but such changes are not used in this study.) Because the boundaries were set as the Canadian boundary, the data on CO2 emissions in North Dakota are not included in this article. However, the energy uses for compressions would be approximately 413 kJ/kg of CO2.3 In the oil field, the compressed CO2 is injected generally in alternating slugs with water, termed water-alternating-gas (WAG), to drive incremental oil to the production wells. The CO2 reduces the oil viscosity and causes significant swelling of the oil when injected as a supercritical fluid. At the surface, the produced oil is then separated from the CO2 and water and placed in a pipeline for delivery to a refinery. At the refinery, crude oil is processed to produce a slate of hydrocarbon products (gasoline, diesel, etc.). The processes of oil production, transportation, and utilization themselves, as shown in Figure 3, bring

Figure 3. Schematic of the CO2 stream from the oilfield through the oil consumer.

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about CO2 emissions to the atmosphere. Nevertheless, with CO2 enhanced oil recovery, the process can act as a CO2 sink as well. This study confines the CO2 stream to the source, oil field, transportation, and refinery (assuming that all of the input carbon to the refinery is ultimately combusted). After CO2 is injected into the reservoir, some CO2 and water are carried along with the oil. CO2 and water are separated at the surface from the oil and re-injected separately into the reservoir. The re-injected CO2, which includes other produced gases, is assumed to be 90% pure (there is currently no attempt to capture the hydrocarbon gases recovered with the oil; the entire gas stream is re-injected). There is a hidden CO2 emission in the process of recycling CO2 from compressor electricity usage and the process of crude oil transportation from electrically driven pumps. SaskPower, the Saskatchewan electrical utility, which has a CO2 emission rate of about 790 kg/MWh, based on the generation mix for SaskPower (2003),4,5 provides the electricity. CO2 emitted from the CO2 recycle process is 0.06 tonne per 1 tonne of CO2 recycled. For the 25-year period considered, there will approximately be 1.40 million tonnes of CO2 emitted from the recycling of 23 million tonnes of CO2 over the entire lifetime of the EOR project, based on EnCana’s original estimation.6 The overall process is closed-loop with all produced CO2 captured and re-injected. Essentially all of the CO2 purchased from DGC is, therefore, assumed to remain in the reservoir and is deemed to be stored. Therefore, the net storage is 18.60 million tonnes of CO2 because of the CO2 emitted during the compression process based on the assumption of 23 million tonnes of recycled CO2. The CO2 stream assigned to the oil consumer is CO2 emitted from refinery processes and CO2 from oil product combustion. The Canadian Industrial Energy End-use Data and Analysis Centre provides a range of values for the CO2 intensity of Canada’s downstream petroleum industry. In 2002, the average CO2 intensity published by the Centre7 was 160 tonnes per 1000 m3 production. Based on the estimate of total incremental oil production noted above, there will be 3.3 million tonnes of CO2 production from the refining of 130 million barrels of crude oil. The CO2 emission from the oil-products usage of the 130 million barrels of crude oil is 61 million tonnes. This calculation is based on Natural Resources Canada (NRCan) standard emission numbers. The CO2 emission conversion factor of medium oil, the average of light oil and heavy oil, is 2.96 tonnes per kiloliter of liquid fuel.8 This calculation is based on the conversion of the carbon in different fuels or the crude oil to carbon dioxide and assuming complete oxidation of all the carbon. There might be some double-counting built into these assumptions because some of the oil might be used for process heat in the refinery process itself rather than becoming part ofthe product slate. The numbers used in this study will, therefore, be conservative estimations of the CO2 released. Economic Optimization As with the basic goal for any commercial project, the objective for undertaking economic optimization on a CO2 enhanced oil recovery project is to maximize the benefit to the project operator. This study presents an alternative objective for a CO2 EOR and storage project. Because of a potential emissions trading approach to controlling greenhouse gas emissions, it would be advantageous to consider storing CO2 in the depleted oil reservoir, which could, in turn, provide an extra source of revenue from selling the credit from CO2

Table 1. Fundamental Values of GLP Factors factor

definition

A1 A2

cost of purchasing CO2 cost of CO2 recycle

A3 A4 B1 B2

revenue of CO2 storage revenue of oil purity of CO2 recycle CO2 requirement to recover incremental oil CO2 emission rate from recycle process CO2 supply limit CO2 recycle limit expected oil recovery

B3 C1 C2 C3

value $20 U.S. per tonnes of CO2 $2.52-2.83 U.S. per tonne of recycled CO2 $0.0001 U.S. per tonne of CO2 $41.50 U.S. per barrel 1 0.3308 tonne per barrel 0.0576-0.0645 tonne per tonne recycled 20 million tones 23 998 750-26 882 250 tonnes 130 million barrels

emission reductions. Therefore, the objective of this study on economic optimization for CO2 EOR and storage is to maximize the CO2 storage while either maximizing the incremental oil or maintaining it at least equal to that of traditional CO2 EOR. In this article, a gray linear programming (GLP) model is applied to solve the objective function. This model allows the inclusion of uncertainty in coefficients and constants. The advantages of gray linear programming include direct incorporation of uncertainty, flexibility of results interpretation, generation of decision alternatives, reasonable computational requirements, and applicability to practical problems. The algorithm of GLP is as follows

objective function: max f( ) A(X( constraints: B(X( g C( where A(, B(, and C( are interval numbers. The factors have the fundamental values reported in Table 1. The objective function and constraints can then be formulated as follows

objective function: max f( ) A1( X1( + A2( X2( + A3( X3( + A4( X4( subject to: X1( + B1(X2( - B2(X4( g 0 X1( - B3(X2( - X3( g 0 X1( e C1 X2( e C2 X3( > 0 X4( e C3 X1(, X2(, X4( g 0 In this study, limits are placed on the components of the inputs into the program. The components in the objective function consist of CO2 delivered, CO2 recycled, CO2 stored, and incremental oil. Moreover, because of the limitation of physical resources, such as CO2, oil, etc., the constraints play an important role in making a decision in a project. This study focuses on the following constraints of the model: injection rate constraint, net storage constraint, CO2 supply constraint, CO2 recycle constraint, and oil expectation constraint. Sensitivity Analysis Because a goal of any project is to operate it economically, the purpose of undertaking sensitivity analysis is to identify the

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Table 2. CO2 Streams at the Weyburn Oilfield stream CO2 purchased CO2 recycled CO2 injection CO2 emitted from recycle process CO2 net storage

Table 4. Results of Economic Optimization Model

capacity (million tonnes) 20 (15 years) 23 (25 years) 43 1.40 18.60

Table 3. CO2 Emission Comparison of CO2 EOR and Tar-Sands process

relative CO2 emissions (%)

CO2 EOR conventional oil tar-sands

70 100 130

possibility of producing more benefit from the project. A sensitivity analysis is the process of varying model input parameters over a reasonable range and observing the relative change in model response. The methodology of the sensitivity analysis demonstrates the sensitivity of the model simulations to uncertainty in the coefficients of the objective function within the optimization model. These are the cost of purchasing CO2, revenue from CO2 storage, and revenue from oil. The CO2 recycle parameter is not involved in the sensitivity analysis because the major cost for recycling the CO2 is from the energy consumption, which is assumed to be a fixed cost, as the project is designed not to release CO2 to the atmosphere. In addition, with a higher oil price, the oil field lifetime is likely to be longer. CO2 recycle will be practical for enhanced oil recovery with an extended lifetime of the field. (It is assumed that, under the original scenario, oil production would cease when the value of production equaled the cost of production and CO2 and water recycling.) Results and Discussions The gross CO2 storage has the same value as the delivered CO2. The actual amount of CO2 that will be stored at the Weyburn unit is currently estimated at 20 million tonnes. However, there is the hidden CO2 emission from the recycle process. This calculation of CO2 emitted is from the standard values for energy required and CO2 emissions from this energy consumption for Saskatchewan, Canada. Therefore, the CO2 net storage for the life-cycle analysis of CO2 at the oil field is calculated when emitted CO2 is considered. Exclusive of the CO2 emission from the CO2 source (the compression of CO2 at the source for injection into the pipeline), the CO2 storage in this enhanced oil recovery project has the capacity to store approximately one-third of the amount of CO2 emitted from the EOR process through the refinery and oilproduct usage. Table 2 lists the streams of CO2, together with their quantities at the Weyburn oilfield. It should be noted that the amount of the CO2 stored reflected in this study is not the total reservoir volume available to store CO2, but just the volume of CO2 stored as a result of the economically optimum use of CO2 for oil production. In other words, in a project designed for CO2 storage, the volume that could be injected into the reservoir would be considerably higher than that in a project designed to extract oil in the most economic fashion. CO2 EOR and storage is, however, a very desirable process for achieving CO2 emissions reductions. From Table 3, it is shown that the CO2 EOR and storage process has the capability of reducing CO2 emissions by at least 30%, as compared to tar-sands operations, which increase CO2 emissions by approximately 30%, compared to a conventional oil operation.9,10 In other words, according to a full life-cycle analysis, the

variable CO2 purchased CO2 recycled CO2 stored incremental oil

capacity 20 million tonnes 23-26.88 million tonnes 18.27-18.62 million tonnes 133.00-141.72 million barrels

emissions of CO2 from oil produced from a CO2-based EOR operation are only two-thirds of the life-cycle emissions of conventional oil production. Tar-sands (and other heavy oil) operations emit additional CO2 because they require upgrading to a marketable crude oil before they can be used in refineries to produce gasoline and other fuels. The objective function of economic optimization with the assumption of producing at least 130 million barrels of oil is determined from the results of the variables shown in Table 4. The maximum incremental oil is estimated to be 141.72 million barrels. This model considers four main elements, which include both expenses and revenues. CO2 purchased and CO2 recycled definitely bring some of the major costs to the project, but CO2 storage can provide an advantage to the project from selling the CO2 credits in the event that emissions trading is implemented. This revenue calculation excludes capital costs, taxes, and other operating costs. Incremental oil is the most important income driving the project. The other case evaluates the maximum net storage in the event that CO2 credits can bring about a revenue stream sufficient to make storage a primary outcome of the project. As a result of this revenue stream, the net benefit to the project owner can be increased, even though, for economic purposes, CO2 storage is established from the amount of CO2 injected excluding the amount of CO2 recycled, and there is a physical limit on the maximum storage capacity of the reservoir of about 90 billion cubic meters. This amount of gross storage is based on the assumption that the miscibility of CO2 is 30% in residual oil, 30% gas saturation, and 40% water saturation for 1 m3 of pore volume at 15 MPa. This calculation uses an area of 180 km2 and a thickness of 20 m with 20% porosity as average values for calculating the maximum storage capacity in the short term (in other words, there is limited dissolution of CO2 in the water in the reservoir in the early stages). In summary, the Weyburn project is economical, as demonstrated by the economic optimization models. The CO2 injection cost is verified at about $3.35 U.S. per barrel of oil production. This cost is reflected as one of the major costs, which also include the cost of purchased CO2 ($20 U.S. per tonne of CO2) and the cost of CO2 recycling ($2-3 U.S. per tonne of CO2) based on 141.72 million barrel of incremental oil production. It should be noted, however, that the CO2 costs are heavily loaded at the front end of the project: in the early stages, the project must buy CO2 with little recycled CO2 to lower the net cost. Later in the project, the CO2 is entirely recycled, leading to lower operating costs. This study includes sensitivity to the cost of purchasing CO2, potential revenue from CO2 storage or CO2 emissions reduction credits, and oil revenue. Each circumstance is based on the Weyburn unit oil production, particularly the forecast of incremental oil affected by CO2 injection. The purchased CO2 is one of the major costs for the Weyburn project. The net revenue is decreased when the cost of CO2 rises. If emissions trading is implemented, it is possible for the Weyburn project to earn more revenue from either selling the CO2 emissions reduction credits or receiving a carbon tax return in the event that CO2 is valued by means of a tax. Once again, without the CO2 emissions reduction credit, the project tends to purchase less new CO2 because it is more expensive than the cost of

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Figure 4. Economic cutoff points.

recycling CO2. At some point, the value of CO2 would cause the project to become driven by the amount of CO2 it could store, which would change injection strategies to put water in a shallower horizon and use continuous CO2 injection. It is also worth noting that any credits would apply during the period of CO2 purchase, not during the period of CO2 recycling, with benefits significantly affecting the early costs (and net present value) of the project. Additionally, the conversion of a project to being dominantly storage-related could shorten the overall lifetime of the project, leaving more oil in the ground because the recycle phase has no value from a storage perspective. For the purposes of this study, the price of CO2 can be considered as a proxy for the value of CO2. As the value of CO2 increases, based on a credit for CO2, the price seen by the oil company effectively decreases. As the value of CO2 surpasses the cost of CO2, the cost becomes negative, and CO2 has an incremental value for the producer. This produces a potential anomaly. If the cost of CO2 drops below the cost of recycling, then it would make sense for an oil company to release CO2, produced back with the oil, to the atmosphere. This, of course, would not happen. The only reason that CO2 could have a cost less than the recycle price of CO2 is by means of credits or taxes giving CO2 a value. As such, any CO2 released would result in a cost for the oil producer and so would not happen. In addition, the oil price is the most important factor for the Weyburn Project economics because it is the main revenue source for the project. The oil price during the end period of the lifetime of the project is of particular interest to the net storage aspect of the project. If the oil price rises, the Weyburn Project lifetime might be extended by continuing to produce oil by recycling the CO2. The limitation to this production is based on the cost of operations escalating at 2% per year. At the point at which the value of production equals the cost of producing the oil, it is assumed that the operation will be ended and the field shut down. The end of the year 2025 is currently predicted to be the economic cutoff point for the project, but this is based on much lower oil price forecasts than exist today. Figure 4 demonstrates the economic cutoff points. It can be interpreted that the lifetime of the project can be extended for almost 1 year if the oil price increases to $50 U.S. per barrel. If the oil price is as high as $60 U.S. per barrel, the project lifetime can be extended for almost 2 years based on the economic cutoff point. The strategies in this paper; therefore, effectively show an alternative approach to dealing with CO2 storage projects, especially with EOR. However, there are existing disparities between oil prices and CO2 value. An increasing oil price will

mean more oil produced, but less CO2 stored because of the longer lifetime of the project and the greater amount of CO2 penalty due to CO2 recycling process. In addition, at some point, the CO2 value will change the economics in favor of incremental storage and potentially lower oil recovery, including a complex set of parameters based on water removal to different geological horizons to provide more void space in the reservoir for CO2 storage as well. If the CO2 cost were $0 (or less than the recycle cost), the CO2 would, in theory, not be recycled unless there were some imperative to capturing the CO2. In reality, there would be a cost to releasing the CO2 back to the atmosphere under these circumstances, rather in the manner of the Statoil project in the North Sea where taxes provide the incentive to store the CO2 geologically as opposed to releasing it to the atmosphere. Conclusions CO2 EOR and storage is an option for reducing CO2 emissions to the atmosphere. Life-cycle analysis can be applied to understand CO2 storage as part of CO2 EOR. The International Energy Agency (IEA) Greenhouse Gas R&D Programme Weyburn CO2 Monitoring and Storage Project is a study of CO2based enhanced oil recovery at the Weyburn unit in southern Saskatchewan, Canada. The cycle of CO2 is explained by the basic elements of the fossil-energy chain. Defining CO2 storage as CO2 net storage is one method of assessing the impact of CO2 storage as opposed to relying on CO2 gross storage, because a CO2 EOR project is a closed loop, so there is an energy penalty associated with direct oil-field operations. The results show that this enhanced oil recovery project has the capacity to store approximately one-third of the total CO2 emissions from the EOR process through the refinery and oil production usage. In effect, this measures the CO2 avoided as opposed to the gross CO2 storage volume. This methodology can be applied to any other storage projects, including deep saline aquifer storage, depleted gas reservoir storage, and oceanic storage, etc., where there are penalties for compression or other handling of the CO2, such as transportation by ship to the storage location in an oceanbased storage system. This study has demonstrated the opportunities for economic optimization by gray linear programming (GLP). In summary, the economic optimization models, a simple decision-making tool to launch a CO2 EOR and storage project, have demonstrated that the project is economical, but that the economics could be improved under a number of different price and operating scenarios. Moreover, the optimization is a result of

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economic and engineering interplay of what is feasible. This work has generally only been taken to the point of basic optimization by the oil company. Aside from the CO2 EOR and storage project, there is a potential to develop the model for any other project if the parameters are available. The economics of CO2 storage with EOR is presented to the level of understanding the key parameters for optimization, examining net storage benefits, and creating a template for understanding how the sensitivities affect storage and economics. Moreover, the sensitivity analysis has not only confirmed that the Weyburn project is economical, but also suggested potential approaches to improve the profitability of the project. One of these methods is assessing the impacts of a lower CO2 cost (considered a proxy for CO2 having a value on the market) with some qualifications as described in the previous section. When emissions trading takes place, CO2 EOR and storage will be more valuable. In addition, the sensitivity analysis has shown that the lifetime of the project extensively depends on the price of oil. As a result, if the oil price increases higher than 60 U.S., the project lifetime can be extended by over 2 years. Literature Cited (1) Taber, J. J.; Martin, F. D.; Seright, R. S. EOR Screening Criteria ReVisitedsPart 2: Applications and Impact of Oil Prices; SPE Petroleum Reservoir Engineering: Richardson, TX, 1997. (2) Wilson, M.; Monea, M. IEA GHG Weyburn CO2 Monitoring & Storage Project Summary Report 2000-2004. Presented at the 7th Interna-

tional Conference on Greenhouse Gas Control Technologies, Vancouver, Canada, September 5-9, 2004. (3) Carbon Dioxide Storage Potential and Costs; Ecofys in cooperation with TNO Global: Utrecht, The Netherlands, 2004. (4) Climate Change Action Plan Progress Report; SaskPower: Saskatchewan, Canada, 2001. (5) EnVironment Report; SaskPower: Saskatchewan, Canada, 2004. (6) PanCanadian Petroleum Limited. Weyburn Unit CO2 Miscible Flood EOR Application; Submission to Saskatchewan Energy and Mines, Saskatchewan, Canada, Nov 1997. (7) Canadian Industry Energy End-use Data and Analysis Centre. A ReView of Energy Consumption in Canadian Oil Refineries 1990, 1994 to 2002; Prepared for Canadian Petroleum Products Institute and Canadian Industry Program for Energy Conservation, Simon Fraser University: Vancouver, Canada, Jan 2004. (8) Analysis and Modeling Group National Climate Change Process. Canada’s Emission Outlook: An Update; Natural Resources Canada, Ottawa, Ontario, Canada, 1999. (9) An Action Plan for Reducing Greenhouse Gas Emissions: Action Plan and 2003 Progress Report for the Syncrude Project submitted to VCR Inc.; Syncrude: Fort McMurray, Alberta, Canada, Jul 2004. (10) Canada’s Climate Change Voluntary Challenge and Registry Program: Ninth Annual Progress Report; Suncor Energy: Calgary, Alberta, Canada, Oct 2003.

ReceiVed for reView August 4, 2005 ReVised manuscript receiVed October 29, 2005 Accepted November 7, 2005 IE050909W