Assessing the Potential for CO 2 Enhanced Oil Recovery and Storage in Depleted Oil Pools in Southeastern Saskatchewan

Assessing the Potential for CO 2 Enhanced Oil Recovery and Storage in Depleted Oil Pools in Southeastern Saskatchewan Gavin K.S. Jensen 1 Parts of this publication may be quoted if credit is given. It is recommended that reference to this publication be made in the following form: Jensen, G.K.S. (2015): Assessing the potential for CO2 enhanced oil recovery and storage in depleted oil pools in southeastern Saskatchewan; in Summary of Investigations 2015, Volume 1, Saskatchewan Geological Survey, Saskatchewan Ministry of the Economy, Miscellaneous Report 2015-4.1, Paper A-5, 7p. Abstract This study identifies oil pools in Phanerozoic strata in southeastern Saskatchewan that have the potential for CO2 enhanced oil recovery (EOR) and subsequent CO2 storage. The province of Saskatchewan hosts numerous depleted oil pools, many of which have been producing for over 60 years. Most of these pools have undergone vertical and horizontal infill drilling, and water flooding. Tertiary, EOR techniques are required to extract more oil from these depleted pools. The Weyburn and Midale pools are successful examples of CO2 EOR, which has increased oil production from 62 900 m 3 (10 000 barrels) per day pre CO2 injection to 176 120 m 3 (28 000 barrels) per day during CO2 injection. Additionally, 30 million tonnes of injected CO2 has been stored in the Weyburn and Midale pools since CO2 flooding commenced in 2000. Results presented in this study include a list of potential pools in southeastern Saskatchewan that would be best suited for CO2 EOR and storage, based on reservoir properties and production history. Keywords: Saskatchewan oil pools, CO2 storage, CO2 enhanced oil recovery, Weyburn, Midale 1. Introduction Saskatchewan is host to numerous oil and gas pools throughout the Phanerozoic sequences in the Western Canada Sedimentary Basin, with some pools producing since the 1950s. Such pools are ideal candidates for CO 2 enhanced oil recovery, as they have undergone infill drilling, water flooding and possibly horizontal drilling; thus, tertiary recovery techniques are required to extract more oil from these pools. Enhanced oil recovery (EOR) by the injection of a miscible gas into a reservoir (also called miscible flooding) is a process whereby a gas is injected to reduce the interfacial tension between the oil and water in the reservoir, allowing for increased displacement of the oil and to increase pressure in the reservoir. The most common miscible gas used in EOR is carbon dioxide (CO 2). This study set out to investigate the feasibility of CO 2 EOR and subsequent CO 2 storage in depleted oil fields in the southeastern part of Saskatchewan by identifying pools with the greatest potential for increased hydrocarbon production via the EOR process, and storage of the injected CO 2 in the depleted reservoirs. Diverting CO 2 gas that would have been released to the atmosphere into depleted oil reservoirs is an effective means of reducing greenhouse gas emissions (Bachu, 2000). CO 2 flooding is an effective tertiary EOR process that has been successfully applied in southeastern Saskatchewan. There, the Weyburn and Midale pools have been under CO 2 EOR flooding since 2000, using CO 2 that comes partially from a major CO 2 emitter in southeastern Saskatchewan, and partially from an emitter in Beulah, North Dakota. The pools are currently producing 176 120 m 3 (28 000 barrels) of oil per day, of which 113 220 m 3 (18 000 barrels) is incremental production as a result of the CO 2 injection (Wildgust, 2013). About 30 million tonnes of CO 2 that would otherwise have been released to the atmosphere had been stored in the Weyburn and Midale pools as of December 2016. These statistics show that increased use of CO 2 EOR and CO 2 storage in the province can be economically significant, not only by improving recovery from oil pools, but also by reducing the province s CO 2 emissions. 1 Saskatchewan Ministry of the Economy, Saskatchewan Geological Survey, 201 Dewdney Avenue East, Regina, SK S4N 4G3 Although the Saskatchewan Ministry of the Economy has exercised all reasonable care in the compilation, interpretation and production of this product, it is not possible to ensure total accuracy, and all persons who rely on the information contained herein do so at their own risk. The Saskatchewan Ministry of the Economy and the Government of Saskatchewan do not accept liability for any errors, omissions or inaccuracies that may be included in, or derived from, this product. Saskatchewan Geological Survey 1 Summary of Investigations 2015, Volume 1

In this study, only large-scale (greater than 500 000 tonnes/year) CO 2 emitters were identified, since it is not currently economically feasible to capture the lower volumes of CO 2 released from smaller-scale emitters. The major CO 2 emitters (greater than 500 000 tonnes/year; Table 1) and oil pools in southeastern Saskatchewan are displayed in Figure 1. Table 1 Large-scale (greater than 500 000 tonnes/year) CO2 emitters in southeastern Saskatchewan. (Data from Environment Canada, from 2014, using a minimum of 500 000 tonnes; http://www.ec.gc.ca/ges-ghg.) Facility Name Plant Type City Greenhouse Gas (tonnes CO2) Boundary Dam Power Station Electricity Generating Estevan 4 994 430 Poplar River Power Station Electricity Generating Coronach 4 641 652 Shand Power Station Electricity Generating Estevan 2 080 808 Co-op Refinery-Upgrader Complex Petroleum Refining Regina 1 618 693 Mosaic Potash Mine Belle Plaine Chemical Production Belle Plaine 679 598 Yara Mine Belle Plaine Inc. Chemical Production Belle Plaine 643 971 Figure 1 Distribution of oil pools and large-scale CO2 emitters in southeastern Saskatchewan. (CDN = Canada, MB = Manitoba, SK = Saskatchewan.) Saskatchewan Geological Survey 2 Summary of Investigations 2015, Volume 1

2. Oil Pool Screening Criteria The Saskatchewan Ministry of the Economy s 2013 Oil Reserves Summary (Saskatchewan Ministry of the Economy, 2013) is the source of reservoir data used in this study. Note that pools classified as Miscellaneous by the Ministry of the Economy, due to a limited quantity of wells within each pool, were excluded from this study. Following the methods of Shaw and Bachu (2002) and Taber et al. (1997), this study employed a filtering method for determining which oil pools would be the best candidates for CO 2 EOR and CO 2 storage, using parameters that would likely be used by oil companies. The author also added a screening criterion of greater than five million cubic metres of original oil-in-place (OOIP). This was done to remove pools that do not have an adequate volume of oil to warrant a large-scale CO 2 EOR and storage project. This study used the framework from other studies (Taber et al., 1997; Bachu, 2004) and made modifications to their screening criteria because some parameters that were used in these previous studies could not be used for this project. For example, reservoir pressure could not be used due to the absence of accurate and reliable data, as the Government of Saskatchewan does not require reservoir pressures to be reported. It was necessary, therefore, to assume there was enough pressure remaining in the reservoir to maintain a miscible CO 2 flood. This assumption is based on the fact that all the pools in southeastern Saskatchewan have been produced under a water flood, which limits the amount of pressure depletion that occurs while the well is on production. Additionally, to determine the remaining or current oil saturation, pressure data is required. As pressure data is not available, the following assumptions were made: It was assumed that reservoir conditions were kept above the oil bubble-point pressure during production history, meaning all gas produced at surface was in solution in either the oil or brine at reservoir conditions. For mass balance purposes, it was also assumed the volume of oil and water being produced from the reservoir was replaced by brine via water flooding or migration of brine into the productive portion of the reservoir (a voidage replacement ratio equal to 1). Screening parameters used include original oil in place; oil density; production depth; current recovery factor; and current oil saturation. All of these parameters were also used by Bachu (2004) and Taber et al. (1997), except for OOIP. Oil density is an important factor in determining good candidates for CO 2 EOR, as it influences oil s mobility and subsequent production volume. An oil density of less than 900 kg/m 3 (API greater than 26 degrees) was used as a cut-off to further narrow down ideal pools (Bachu, 2004), where pools with the heavier oils were eliminated. Next, pools with a production depth of greater than 1000 m were used to determine if CO 2 would be miscible (miscibility refers to whether two fluids can be mixed together to form a single phase). CO 2 storage can be performed in either miscible or immiscible conditions; however, miscible conditions have much greater storage potential than immiscible conditions. For CO 2 to be miscible, the reservoir temperature and pressure have to be greater than 31.1 C and 7.36 mpa, respectively, as shown by the supercritical region on the phase diagram for CO 2 (Figure 2). Typically, the reservoir depth in southeastern Saskatchewan required for miscible flooding is approximately 1000 m, since it s at this depth the reservoir would meet the necessary temperature Figure 2 CO2 phase diagram (modified from Bachu, 2004). The supercritical field marks the temperature and pressure within a reservoir where CO2 becomes miscible. (mpa = millipascals.) and pressure for the CO 2 to be in the supercritical phase (Bachu, 2004). Saskatchewan Geological Survey 3 Summary of Investigations 2015, Volume 1

A current minimum recovery factor of 25% was used to further define the oil pool suitability. A high recovery factor typically indicates favourable reservoir conditions for oil production. Pools with high recovery factors are typically excellent candidates for miscible flooding. Low recovery factors in pools could be due to factors such as high reservoir heterogeneity, thinner beds, and low sweep efficiency (the fraction of the area from which reservoir fluid is displaced by the injected fluid, affected by API density and pressure within the reservoir). These factors will decrease the total recovery of the oil and in turn decrease the volume of CO 2 that could potentially be stored in the reservoir. A current minimum oil saturation of 20% was used to further define pool desirability. This would ensure there is enough oil remaining in the reservoir to merit a CO 2 EOR project. To determine current oil saturation, the reservoir pore volume was calculated using data from the 2013 Oil Reserves Summary (Saskatchewan Ministry of the Economy, 2013). The initial water and oil volumes were determined using the initial water saturation value from the reserves summary (ibid). The oil production volume was subtracted from the initial oil volume, resulting in the current oil volume in the reservoir. It is worth noting that the formation volume factor of oil in this calculation (included with the initial reserves data) is assumed to be a constant value. The screening processes used in this study, along with the number of pools meeting the criteria, are summarized in Figure 3. Figure 3 Oil-pool screening criteria used in this study and number of wells meeting the criteria at each stage of the screening process. (OOIP = oil in place.) 3. Results When the results of the screening process were evaluated, a list of 20 oil pools was identified as being the most viable candidates for CO 2 EOR and storage (Table 2). This list only includes pools suitable for miscible flooding; as discussed previously, miscible conditions result in the greatest potential volume of CO 2 that could be injected while maximizing the amount of oil displaced and therefore the amount of storage space for CO 2. The list of 20 pools is topped by the currently CO 2 flooded Weyburn and Midale pools, which have the greatest volume of initial oil in place of all the pools that met the screening criteria and therefore the greatest potential for additional oil recovery and amount of CO 2 storage space available. This result demonstrates the validity of the screening criteria used in this study. Saskatchewan Geological Survey 4 Summary of Investigations 2015, Volume 1

Table 2 Oil pools in southeastern Saskatchewan that are the top candidates for viable CO2 EOR and storage, as determined by the screening criteria used in this study. The order in which the pools are listed is based on initial oil in place (IOIP), with pools having the greatest volume of IOIP at the top of the list, and the remainder listed in descending order of IOIP volume. Original Oil in Estimated Current Oil Place Oil Density Prod. Depth Recovery Saturation Pool Horizon (1 000 000 m 3 ) (kg/m 3 ) (m) (%) (%) Weyburn Midale (unit) 176.2 880 1399 50 34 Midale Central Midale (unit) 81.7 877 1402 33 40 Queensdale Frobisher-Alida (non-unit) 29.4 850 1173 35 63 East Steelman Midale (unit vi) 25.3 843 1399 40 65 Alida West Frobisher-Alida 19.9 836 1143 25 67 Innes Frobisher 14.3 891 1333 31 47 Nottingham Alida (North Alida Beds unit) 12.8 839 1066 33 47 Alida East Frobisher-Alida (unit) 11.2 824 1122 46 67 Lost Horse Hill Frobisher-Alida (voluntary unit 9.6 848 1174 30 22 no. 1) Rosebank Alida (voluntary unit no. 1) 9.6 828 1067 46 20 Star Valley Frobisher-Alida 9.2 862 1162 43 37 Flat Lake Ratcliffe (voluntary unit no. 1) 8.2 865 1956 28 35 Ingoldsby Frobisher-Alida (voluntary unit) 6.2 865 1089 58 69 Skinner Lake Ratcliffe 5.8 893 1723 34 45 Kenosee Tilston (voluntary unit) 5.5 848 1196 46 36 Ingoldsby Frobisher-Alida 5.4 876 1089 35 63 White Bear Tilston 5.4 862 1060 33 40 Kisbey Frobisher-Alida (voluntary unit 5.3 840 1195 27 57 no. 2) Sherwood Frobisher 5.1 880 1240 42 38 Elmore Frobisher (voluntary unit) 5.0 871 1219 46 31 4. Discussion The oil pools that meet the screening criteria, and the major CO 2 emitters (>500 000 tonnes) are displayed in Figure 4. Figure 4 illustrates the close proximity of some sources (emitters) to potential sinks (oil and gas pools). As is evident, a number of large-scale CO 2 emitters mainly coal-fired power plants are located in the southeastern part of the province. Fortunately, these emitters are in close proximity to some of the top candidates for miscible CO 2 EOR. This proximity reduces the cost of infrastructure needed to facilitate transportation of CO 2 from the major emitters to the storage pools. Additional research could be conducted to further refine and characterize the reservoirs of the top candidate pools. This would include investigating possible reservoir heterogeneity, in terms of variation in net pay, porosity and permeability within the reservoir. Saskatchewan Geological Survey 5 Summary of Investigations 2015, Volume 1

Figure 4 Large-scale CO2 emitters, and the oil pools in southeastern Saskatchewan that meet the screening criteria. (CDN = Canada, MB = Manitoba, SK = Saskatchewan.) 5. Conclusions The province of Saskatchewan has great potential for more widespread use of CO 2 EOR and storage as there is an abundance of oil pools in the southeastern portion of the province that are excellent candidates for miscible CO 2 EOR. Additionally, there are large-volume CO 2 emitters in relatively close proximity to the depleted hydrocarbon pools that are top candidates for CO 2 storage. This source sink matching greatly decreases the infrastructure required to implement large-scale oil recovery and CO 2 storage projects. More widespread use by industry of CO 2 EOR and storage would be a great benefit for the province in terms of producing more hydrocarbons from reservoirs not conducive to production using conventional techniques, and reducing the province s greenhouse gas emissions by CO 2 storage in the eventually depleted reservoirs. The success of the CO 2 EOR in the Weyburn and Midale pools should act as a catalyst for other companies to invest in CO 2 EOR in Saskatchewan. Saskatchewan Geological Survey 6 Summary of Investigations 2015, Volume 1

This report showcases the potential for CO 2 EOR and CO 2 storage in the province and is a good first step in the aim of assisting oil companies in determining which pools are the best candidates for CO 2 EOR and storage within southeastern Saskatchewan. 6. Acknowledgments The author would like to acknowledge Michael Nelson for his insight and knowledge of reservoir engineering and for his assistance in developing the principles that helped to base the assumptions made in this study. 7. References Bachu, S. (2000): Sequestration of CO2 in geological media: criteria and approach for site selection in response to climate change; Energy Conversion and Management, v.41, p.953-970. Bachu, S. (2004): Evaluation of CO2 Sequestration Capacity in Oil and Gas Reservoirs in the Western Canada Sedimentary Basin; Alberta Energy and Utilities Board, 77p. Saskatchewan Ministry of the Economy (2013): 2013 Oil Reserve Summary Report; Saskatchewan Ministry of the Economy, Resource Management Branch. http://publications.gov.sk.ca/details.cfm?p=4705 Shaw, J.C. and Bachu, S. (2002): Screening, evaluation, and ranking of oil reservoirs suitable for CO2-flood EOR and carbon dioxide sequestration; Journal of Canadian Petroleum Technology, v.41, no.9, p.51-61. Taber, J.J., Martin, F.D. and Seright, R.S. (1997): EOR screening criteria revisited Part 1: Introduction to screening criteria and enhanced recovery field projects; SPE Reservoir Engineering, v.12, no.3, p.189-198. Wildgust, N., Gilboy, C. and Tontiwachwuthikul, P. (2013): Introduction to a decade of research by the Weyburn Midale CO2 Monitoring and Storage Project; International Journal of Greenhouse Gas Control, v.16, Supplement 1, p.1-4. Saskatchewan Geological Survey 7 Summary of Investigations 2015, Volume 1