Technical Report

Alberta CO 2 Purity Project
Petroleum Technology Alliance Canada

Executive Editor’s Note
Carbon capture and storage (CCS) strategies involve capture, transportation, and storage stages. CO 2 purity can have significant impacts on these stages. The Alberta CO 2 Purity Project (ACCP) led by Petroleum Technology Alliance Canada (PTAC), in partnership with the Integrated CO 2 Network (ICO 2N), examined these impacts and concluded with a technoeconomically balanced model.  This model can be applicable to governments and industry for developing CO 2 purity guidelines. The article is an abstraction of the original ACCP final report. I hope you will find it enjoyable and inspirational to read. Your feedback regarding this session and the technical content of this article are strongly encouraged. Please send your comments to: JCPT@spe.org.

Dr. Jian-Yang (JY) Yuan, BSc, MSc, PhD
JCPT Executive Editor

The ACPP is an example of a PTAC project that demonstrates benefits such as financial and expertise leveraging by industry working together to identify and address current challenges related to CCS. A total of 32 organizations participated in this project, including producers, transporters, service companies, CO 2 emitters, federal and provincial governments, research providers, and academia. The financial and expertise leveraging from this project is simply outstanding; without this project, it would have cost  a single producer 127 times more money, and substantially more time to achieve the same results, not to mention the value of the expertise leveraging achieved. PTAC’s mission is to facilitate innovation, collaborative research and technology development, demonstration, and deployment for a responsible Canadian hydrocarbon energy industry.

Soheil Asgarpour, PhD, P.Eng
PTAC President


Executive Summary 
PTAC, in partnership with ICO 2N, and over 30 industry entities, has completed ACPP; a project intended to develop strong “made in Canada” purity guidelines that will inform commercial-scale demonstration CCS projects. These guidelines will provide a foundation for accelerated CCS deployment in Canada, and develop an integrated picture of CO 2 requirements from source to sink. It will also advise on the optimum purity requirements for a CCS network, thereby addressing critical knowledge gaps for CCS technology deployment. 

The ACPP is a first of its kind project not only in Canada, but worldwide. Purity specifications have never been evaluated across the entire chain, and more importantly across an entire spectrum of impurities in combination as opposed to focusing on single impurities or processes. In determining optimal CO 2 purity, this will lead to lower costs in overall CCS implementation, ensure proper due diligence is complete before undertaking new projects, and ultimately aid in the overall reduction of greenhouse-gases through further knowledge, safety, and practicality of carbon capture (CC) technology.

The project has developed a detailed technoeconomic model populated with derived data that can analyze system scenarios to determine the effects of impurities and optimize purity levels across integrated CCS infrastructure. This work has thus established purity recommendations that can be used by regulators, academia and industry in Alberta, Canada, and jurisdictions across the globe.

CCS has emerged as one of the few technologies available to achieve the dramatic reductions in carbon dioxide (CO 2) emissions that will be necessary to mitigate global climate change. CCS is composed of the following elements (Fig. 1): 
  • Capture of CO2 emissions from large industrial facilities; 
  • Transportation of the CO2 through pipelines; and 
  • Permanent storage of the CO2 in deep underground formations: 
    • Oil reservoirs where CO2 is used for enhanced oil recovery (EOR); 
    • Deep saline aquifers (sequestration). 
However, CO 2 that is captured from industrial sources is not pure and can contain many impurities. The ACPP examined the effect of CO 2 purity and contaminants on the above four elements of CCS systems. A key result of ACPP is a globally unique technoeconomic model that balances technical and economic considerations and derives a purity guideline that is optimal to all components in the CCS value chain. The model can be used by government and industry to develop purity guidelines across the CCS chain. 

Phase 1 

Phase 1 was a scoping exercise designed to canvas literature and industry knowledge, aggregate the suite of contaminants that need to be evaluated, and to screen and rank each contaminant. This was completed to ensure that future technical analysis would be focused on the appropriate contaminants (i.e., those that are present in larger quantities or greatly affect any one component of the value chain). 

Phase 1 provided the ACPP with some important interim conclusions. The current industrial experience with CO 2 purity is based on geologic CO 2 supply where contaminants are few and generally well understood. As the world moves to capture and use anthropogenic CO 2, the number of potential contaminants increases, including compounds that are poorly understood from the point of view of their impact on CCS. 

There are a large number of discrete CC technologies, and each technology has a unique CO 2 purity and contaminants profile. In addition, the contaminants profile of each CC technology is affected by the industrial process and feedstock to which it is applied, from steel manufacturing to electricity generation. ACPP assembled a list of 21 contaminants based on all major capture processes by collecting data from 17 energy companies. Subsequently, ACPP identified the contaminants that occur in a significant concentration and that have the greatest effect on each of the four elements of the value chain: capture, transportation, EOR, and sequestration. This analysis was completed using existing literature and knowledge, and culminated in the selection of six impure CO 2 compositions typical of the capture and usage scenarios most likely to take place in a Canadian context (Table 1). These six compositions were the basis for the physical and modelling analyses conducted during Phase 2.

Phase 2 

The purpose of Phase 2 was to fill critical knowledge gaps about the impact of anticipated anthropogenic CO 2 compositions on each element of the CCS value chain. 

CO2 Capture Technologies. Phase 2 focused on understanding water solubility and dewpoint in supercritical CO 2 mixtures because as long as water remains in the supercritical phase, corrosion and hydrate formation are minimized. There is much literature with references to the solubility of water in pure supercritical CO 2 and supercritical CO 2 with CH 4 and H 2S impurities over the critical range of temperatures and pressures. However, there is little knowledge regarding water solubility and dewpoint in CO 2 with the types and quantities of impurities typically found in anthropogenic CO 2. These impurities can have a significant impact on the water-carrying capacity of the supercritical fluid.

The solubility of CO 2 in water is determined by the dewpoint, which is determined by changing temperature and pressure and identifying the point at which free water begins to form or at which corrosion takes place. ACPP and Carbon Management Canada engaged two Canadian research groups to undertake complementary studies: 
  • The microfluidics technology of Dr. David Sinton (University of Toronto) used a novel microfluidics technology which required adaptation and validation for use in supercritical CO2
  • Dr. Weixing Chen (University of Alberta) used more conventional technology to undertake corrosion assessments. 
Microfluidic experiments were conducted for pressures up to 2,500 psi and temperatures between 31 and 50°C. Droplet formation and growth was observed within seconds of pressure reduction below the dewpoint pressure. Images were taken at a fixed location over time to track droplet formation and droplet size evolution. For validation, the method was first applied to the well-studied CO 2-water system. The microfluidic results were shown to correspond closely to both previous experimental and theoretical results. 

The method was then applied to determine the dewpoint conditions of water in industrially relevant CO 2 mixtures. The dewpoint conditions for some industrial mixtures remained similar to that of pure CO 2 and water, while impurities in other mixtures reduced the mixtures’ overall solubility for water, indicating a potential increase in pressure requirements for safe transportation. 

Corrosion assessments were conducted on X-65 pipeline steel in various moisture-containing supercritical CO 2 gas-mixture environments. This corrosion approach to determine the dewpoint is reliable and highly sensitive. 

The microfluidic and corrosion methods yielded similar outcomes on an overall basis: the impure CO 2 composition tested would not result in a separate water phase or corrosion if the temperature is maintained above 35°C and the pressure above 1,250 psi when water concentration is at or below the industrially important value of 500 ppm (weight). 

CO2 Transmission Pipeline Transportation. Key issues related to pipeline transportation of CO 2 are (i) the impact of impurities and (ii) wave speed and crack propagation. The latter concerns the possibility of catastrophic running ductile fractures in CO 2 pipelines caused by the difference in speed between the decompression wave and crack propagation. Steel with increased toughness or crack arresters are used to mitigate this concern and much research has been performed in understanding the phenomena, particularly by TransCanada Corporation and NOVA Chemicals. Thus, the ACPP work program was focused on obtaining a better understanding of the effect of anthropogenic impurities on transportation capacity so that unnecessary overdesign parameters could be reduced in order to optimize design, reduce material, and lower construction and operation costs.

The literature review found that indeed the presence of impurities affect pipeline transportation flow capacity. The general effect is that the higher the level of impurities, the higher the reduction in the flow capacity given the same pipeline inlet pressures and flow temperatures. Furthermore, according to the literature, impurities with much lower molecular weight than CO 2 (e.g., H 2 and CH 4) result in higher reductions in flow capacity. It was determined that a typical impurity level of 5% in anthropogenic CO 2 would result in a reduction in transportation flow capacity by approximately 3 to 6%, and that an impurity level of 11% would cause reductions in flow capacity on the order of 7 to 17.5%. However, the literature review did not discover experimental data to substantiate the theoretical work. In addition, published theoretical results were not directly comparable because of variations in equation of state used, as well as temperature and pressure conditions. 

Validation of the outcomes of the literature review was needed and performed by numerical analysis and actual tests in a small pipeline loop. The Phase 2 investigation intended to obtain experimental data from actual flow-loop testing and was conducted at TransCanada’s Gas Dynamic Test Facility in Didsbury, Alberta. The flow loop is 178 m long, nominal pipe size 2 in size and rated up to 22 MPa operating pressure. It incorporates a special pump suitable for CO 2 application, along with necessary mixing and filling capabilities of any mixture of CO 2, including impurities. 

The results of flow-loop testing on the six impure CO 2 compositions as well as numerical analysis on these mixtures indicated that impurities investigated in this study (namely N 2, O 2, Ar, CO, H 2, and CH 4) impact the flow capacity of a pipeline transporting these mixtures in a negative way. That is, these impurities result in a reduction in pipeline-flow capacity relative to pure CO 2 fluid. The degree of flow-capacity reduction in terms of the relative reduction in mass flow rate is directly proportional to one-half of the relative reduction in the mixture density as compared with pure CO 2 fluid, at the same flow condition of pressure and temperature. For example, if the reduction in density of a CO 2+impurity mixture is 6%, the resulting reduction in flow capacity in terms of mass flow rate is 3% at the same condition. Flow capacity is not directly related to the mixture molecular weight as may have been commonly perceived. Both molecular weight and compressibility factor at the prevailing condition of pressure and temperature affect the mixture density, which in turn affects the flow capacity of a pipeline. Hydrogen as an impurity component has the most negative effect on flow capacity. This is primarily because of its effects on dramatically reducing the mixture density at the same flow condition relative to pure CO 2. Impurities were shown to have little effect on the pressure loss coefficients (e.g., friction factor) by the Reynolds number, and hence on flow capacity of a pipeline under the same conditions. 

CO2 EOR. The EOR work program focused on understanding the effects that impurities in CO 2 have on minimum miscibility pressure (MMP), which is the minimum pressure at which the injected gas and oil combine to form a single, uniform mixture. A miscible flood operating at or above this pressure should maximize oil recovery, while floods operating below this pressure will leave unrecovered oil in the reservoir. Most impurities found in anthropogenic CO 2 have a negative impact on the oil-recovery process by increasing the MMP. Laboratory testing was undertaken to gain a better understanding of the magnitude of these impacts, especially with mixtures involving multiple impurities. MMP was tested on one representative oil sample from the Cardium formation in Alberta using two different types of equipment: rising bubble apparatus (RBA) and slimtube. Using these tests, the MMP and the recovery factor slope were determined for Cardium oil for CO 2 containing key anthropogenic impurities. The experimental results compared favorably with the literature. 

With the experimental results, ACPP was able to estimate the negative oil-recovery impact of impurities by applying a standard workflow of reservoir-engineering calculations. The workflow allowed the estimation of loss reserves and production from the presence of impurities as compared with industry experience in Alberta and in the Permian Basin. These outputs were then translated into economic impact in the technoeconomic model. 

CO2 Sequestration in Deep Saline Aquifers. The sequestration work program was mostly concerned with the performance of the storage formation and was focused on better understanding the effect that impurities have on a sequestration scheme’s containment, pore space use efficiency and capacity, plume extent, trapping capability, and injection-scheme performance. 

A parametric study was conducted on impact of impurities on plume dynamics and rate and extent of trapping mechanisms in saline aquifers. The task was mostly a desktop numerical study performed with synthetic simplified cases and generalized models of actual reservoirs. An important observation controlling all study results was that viscosity and density of the mixtures considered were lower than those of pure CO 2 at the same temperatures and pressures. It follows that a plume of CO 2 with impurities, moving updip with no barrier, will therefore migrate farther from the point of injection but will be trapped through residual saturation sooner than will a plume of pure CO 2 and possibly enhance dissolution, primarily because it is exposed to more rock/brine volume. A larger plume, however, means that a larger area must be defined and monitored for leakage pathways (e.g., faults and wells), but the faster trapping translates into a shorter monitoring period. 

Equally important is that contrasts of viscosity and density between pure CO 2 and a CO 2 mixture decrease with depth, suggesting that differences in flow behaviour and storage capacity are reduced proportionally with depth. Experimental rock-fluid interaction studies, including modelling and autoclave experiments, were also performed using samples from siliciclastic and carbonate rocks. Batch experiments were conducted in high-pressure, high-temperature autoclaves with rock samples immersed in synthetic brine and exposed to supercritical CO 2 with and without admixed O 2. Tests of three siliciclastic rocks show that O 2 is likely to alter the geochemistry of subsurface systems in methods that the pure CO 2 case does not, in particular when ferrous-iron bearing minerals are present. One carbonate rock (not containing ferrous minerals) was also tested and it was observed that carbonate grains dissolved unevenly. In all of the autoclave experiments runs, mineral precipitation remained minor because the precursor minerals that supply component ions are not abundant. This suggests that as long as a precursor reactive mineral fraction is a small portion of the rock, O 2 will not have a large geochemical effect on mineral precipitation and therefore on rock stability or fluid flow. 

Phase 3 

The technoeconomic model was developed to tie technical parameters to economic costs in order to quantify impact. Technical data collected in Phase 2 of the study were linked to economic implications that quantified (as a dollar amount) the effects of impurities on an integrated CCS system. For transportation, the data collected helped to define the design parameters that directly affect cost. For EOR, the data collected on the effect that impurities have on MMP were used to determine potential changes in oil recovery, and thus, changes in revenue that results from injecting impure CO 2. For sequestration, the behaviour of impure CO 2 in a geologic formation determined the design of the injection scheme (e.g., number of wells and failures) as well as the measurement, monitoring, and verification requirements and the required pore space, all of which have cost implications. 

The technoeconomic model allows the user to input system parameters (e.g., capture process, pipeline length, and EOR/sequestration allocation) to understand the effect of these inputs throughout the system. The tool’s scenario structure ensures that it is relevant to many diverse users and applications. The user defines input parameters, including capture technologies or combinations of technologies, pipeline length, and end market choice (EOR or sequestration). The model derives a combined CO 2 stream and purity, which are linked to cost factors for each value chain component. These factors are used to calculate cost impacts to each value chain component and to the CCS system in its entirety. The model compares directly the impure CO 2 scenario to a 100% pure CO 2 scenario and determines how the total system and individual components are affected by the presence of impurities. For example, the user is able to input lower purity capture streams, and observe the trade-off of these lower capture costs against resulting higher pipeline costs. 

The model was designed to be flexible for multiple users with varying interests and objectives. It was designed to clearly illustrate the trade-offs between scenarios. This will allow any user to define their own assumptions and run scenarios to see the impacts they are most concerned with. 

Phase 4 

The purpose of Phase 4 is knowledge mobilization and it is now taking place with the publication of ACPP’s Final Report, the distribution of the technoeconomic model to ACPP participants, and presentations at selected industry and academic gatherings. In particular, the technoeconomic model will allow individual companies and government jurisdictions to apply proprietary or regional data in reaching conclusions relevant to their situation.

Conclusion 

The ACPP examined the technical and cost impact of impurities on each of the four elements of the CCS value chain: 
  • Capture of CO2 emissions from large industrial facilities; 
  • Transportation of the CO2 through pipelines; and 
  • Permanent storage of the CO2 in deep underground formations: 
    • Oil reservoirs where CO2 is used for EOR; 
    • Deep saline aquifers (sequestration). 
As the world moves to capture and use anthropogenic CO 2, current industrial experience with geologic CO 2 is not sufficient. With anthropogenic CO 2, the number of potential contaminants increases, including compounds that are poorly understood from the point of view of their impact on CCS. The amount and properties of these impurities will impact the elements of the CCS value chain differently and the purity specification that would optimize performance and cost throughout the CCS value chain is not obvious. 

During Phase 1, ACPP conducted a number of literature searches and consultations with industry and academics in order to understand the current state of knowledge. This led to the identification of knowledge gaps in each of the four CCS value chain elements with respect to the impact of impure CO 2 compositions that are mostly likely to become industrially relevant in Canada.

It also led to the realisation that it is unlikely that there would be a single “made in Alberta” purity specification, and ACPP decided to develop a technoeconomic model that could be used to find the optimum purity for any particular project. 
Phase 2 was composed of a number of laboratory and numerical modelling work packages intended to fill specific knowledge gaps: 
  • The impact of anthropogenic impurities was investigated on the dewpoint of supercritical CO2. Results indicate that if water content is at or below the industrially important concentration of 500 ppm, the presence of typical anthropogenic impurity compositions is not likely to result in the dewpoint occurring within typical industrial pressure and temperature conditions. 
  • The presence of anthropogenic impurities, particularly low molecular weight compounds such as H2, was found to reduce pipeline-flow transportation capacity. The extent of such reduction will depend of the nature and the amount of the impurities. 
  • The impact of natural and anthropogenic impurities of the performance of EOR was quantified in laboratory experiments. All anthropogenic impurities are expected to negatively impact EOR performance. 
  • Impurities were also found to reduce the viscosity and density of CO2 stored in deep saline aquifers, resulting in a larger aerial extent of the stored CO2 plume. The impacts are to increase the scale of regional monitoring infrastructure but to reduce the time of such monitoring. The presence of oxygen could alter the geochemistry of the host rock, in particular when ferrous-iron bearing minerals are present. 
The information analysed in Phase 1 and generated in Phase 2 was integrated into the ACPP technoeconomic model during Phase 3. The ACPP model allows the user to specify the characteristics of the CCS value chain under study and inquire as to the cost impact of various impurity compositions, as compared with industrially pure CO 2. The flexibility of the model will allow individual companies and government jurisdiction to model the impact of CO 2 purification decisions in order to arrive at the optimum design for each situation.

The overarching purpose of ACPP was to bring industry experts and stakeholders together in advance of the critical design milestones leading to 2015. ACPP has evaluated the effects of CO 2 purity and numerous contaminants on the various component parts of CCS, including capture, pipelines, EOR, and sequestration. ACPP also has assisted in the understanding of safety implications of CO 2 purity from an industry perspective, and will provide technical and economic information, based on the collective findings of the project, to regulators governments, and stakeholders to enhance their understanding of the purity issue. Ultimately, the ACPP will define a “made for Alberta purity specification.” 

Acknowledgements
The ACPP Final Report was prepared by PTAC, with major contributions from ICO 2N, Carbon Management Canada, Chevron Corporation, ConocoPhillips Canada, and TransCanada Corporation.

The full report can be found at www.ptac.org.