31. Will drinking water be affected by CO2 storage?

Figure 20. A standard oilfield wellbore, with a pump jack attached. This image is not to scale, and the wellbore stretches down at least 1000 metres into the ground. In a CCS well, the casings and tubing will also typically extend across all of this depth.

The WMP has shown that CO2 can be safely stored in rock formations without affecting drinking water. Between the years 2000 and 2012, the WMP took water samples from drinking-water wells in the area above where CO2 has been injected. The readings in the year 2000 acted as a "baseline" – this means that the readings from these wells showed us what the quality of the water was before injection of CO2 began. These baseline readings were then compared with results that were taken at various points, years after the CO2 injection began. The comparisons between water wells before, during and after injection have shown that no changes have occurred in water quality caused by CO2 injected into the oilfield, and recorded minor changes in well water are likely from natural, seasonal or other causes. Well water in the area continues to meet provincial regulatory standards.

If leakage from a CO2 storage project were to happen into groundwater, it would most likely occur through the wellbores. Wellbores are the holes drilled deep into rock formations like oil and gas reservoirs to both inject substances like CO2 and bring to the surface materials like oil. Wells are cased in metal and cement, especially nearer to the surface, in order to protect drinking water. See Figure 20.

All operating wells are topped with a "wellhead" (see Figure 21) which remains in place during the production or injection life of the well until it is permanently closed (shut in). When a well is no longer in use, the well is "capped" and injected with high volumes of cement to fully seal it.

Figure 21. This CO2 injection well has a wellhead that can be turned off, stopping injection. Wellbores that are not currently producing oil or being used for injection will have a wellhead such as this on the surface. Wells that are no longer in use will have their wellhead removed and will be cemented down the full length of the wellbore to ensure they do not allow for the upward movement of liquids and gases. All surface lines and equipment will be removed and the well will be permanently capped. (Photograph courtesy of Cenovus Energy)

Governments and industry have strict regulations about maintaining the integrity of oil and gas wells.