Two separate investigations have found no evidence to suggest that CO2 is leaking from the Weyburn-Midale CO2-EOR field in Saskatchewan, Canada. In January of last year the Kerr family, who owns property near the Weyburn field, feared that their groundwater and soil had been contaminated by CO2 leaking from the EOR project. Cenovus, the company that operates the Weyburn field, and the International Performance Assessment Centre for Geologic Storage of CO2 (IPAC-CO2) both initiated studies to investigate this complaint.
Equally significant as the conclusion itself are the decisions made by these organizations to take these allegations seriously and investigate vigorously. When this issue arose last year, my colleague George Peridas called for a prompt and thorough independent investigation of the claims. NRDC views geologic sequestration of CO2 as an important tool in the effort to halt climate change. As George wrote, public acceptance and confidence are vital to the continued use and expansion of geologic sequestration. We are pleased that a thorough scientific investigation was undertaken and with the results.
The conclusion reached by both studies that CO2 is not leaking from Weyburn was based on multiple lines of evidence:
- Soil gas and groundwater samples from both studies showed the CO2 on the Kerr property to be biogenic in origin, in other words, to have originated from natural biologic processes in the soil and not leaked from the EOR project. Multiple geochemical parameters were investigated to reach this conclusion including CO2 concentration, stable and radioactive carbon isotopes, noble gases, and fixed gas relationships*.
- A review and testing of pipeline infrastructure and well construction and mechanical integrity found no leaks or potential migration pathways for CO2 and indicated that all infrastructure is sound and operating properly.
- Sediment, surface water, and groundwater sampling showed no or only trace amounts of hydrocarbons, which may have originated from multiple minor sources such as surface spills or from natural biologic processes. All samples met drinking water quality standards.
- A sheen or film present in surface ponds, a well, and wetlands was sampled and found to be bacterial in origin – not consisting of hydrocarbons.
The Cenovus/Trium study was peer reviewed by the Petroleum Technology Research Center and the IPAC-CO2 study was peer reviewed by a panel of subject-matter experts. The peer reviewers found that the designs, methodologies, execution, results, interpretation, and conclusions of both studies were appropriate and reasonable.
This incident is a lesson for future project developers. It reinforces the importance of site characterization, collection of baseline data, robust monitoring, and having in place a plan to address possible leakage. As was done at Weyburn, the right way to address concerns about the performance of geologic sequestration projects is to face them head on with thorough scientific investigation and analysis and we commend these organizations for undertaking this effort.
*For more details on these methods, please see below:
- Carbon Isotopes: The carbon atom has three isotopes: 14C, 13C, and 12C. 14C is radioactive, meaning that it decays over time into a different atom (nitrogen). Because of this, old sources of carbon, such as coal, are depleted in 14C. New sources of carbon are enriched in 14C. The CO2 injected into the Weyburn field is captured from a coal fired power plant, meaning that the carbon in that CO2 is derived from the coal and is therefore depleted in 14C. If the CO2 in the soil samples from the Kerr property originated from the Weyburn field, scientists would expect the CO2 to have this 14C signature. On the contrary, what researchers found was that the CO2 in the soil was enriched in 14C, meaning that it was derived from a modern source – principally natural soil respiration. 13C and 12C are stable isotopes of carbon. By comparing the ratio of 13C to 12C in a sample versus a standard – a ratio abbreviated as δ13C – these isotopes can serve as a “fingerprint” for the source of the carbon. In the case of Weyburn, the δ13C values of natural CO2 sources – such as plants, soils, and groundwater – overlap those of the injected and produced CO2. This means that δ13C alone cannot be used to distinguish natural from injected CO2. However, by comparing δ13C to CO2 concentration, investigators determined that samples from the Kerr property are representative of a mix of atmospheric δ13C CO2 values and the δ13C CO2 values produced by biologic respiration of plants. This indicates that CO2 at the Kerr property is the result of natural biologic processes and not leakage from Weyburn.
- Noble Gases: If you remember back to Chem 101, noble gases are those elements located on the far right side of the periodic table. They are very stable and occur in very small amounts in both natural and anthropogenic CO2. The ratios and isotopic compositions of noble gases are characteristic of their source: they are derived either from the earth’s crust, the mantle (the layer of rock below the crust), or the atmosphere. As such, they can be used as a very effective tracer of CO2 source. Samples from the Kerr property had noble gas concentrations and ratios indicative of an atmospheric source, not a crust or mantle source, indicating that there was no sign of CO2 or fluids having migrated from the Weyburn project.
- CO2 concentration and fixed gas relationships: The amount of CO2 in soil and water was measured to determine whether concentrations fell within those expected due to natural biologic processes or indicated some outside input. Concentrations at the Kerr property were consistent with natural biologic processes and seasonal variations. Investigators also measured concentrations of oxygen (O2), nitrogen (N2) and argon (Ar) gases in soil. Comparing the concentrations of these gases to CO2 concentration can also indicate whether there is input from an outside source. Examining the concentration of CO2 versus O2, CO2 versus N2, and CO2 versus N2/O2 all indicated that gas relationships are those that would be expected from normal biologic processes and do not indicate any leakage of gases from Weyburn.