32. Will topsoil be affected by CO2 storage?

Nearly all soil contains naturally occurring CO2, created by what are called "biogenic" processes – this means that the decaying of plant and animal matter leaves CO2 in the soil. At the beginning of the WMP in 2000, soil gas samples were taken at various locations above the oilfield where the CO2 was going to be injected. These readings showed a wide range of CO2 in the soil (from 2% to 11%). The readings were then used as a baseline to compare with soil gas samples that continued to be taken at those same locations in the next 10 years.

Figure 22. Soil gas samples are taken in a field above the Weyburn oil reservoir. (Photograph courtesy of the PTRC)

A comparison of soil before and after injection showed that there has been no increase in CO2 in the soil attributable to the storage of CO2 in the Weyburn oilfield after 12 years of measurements; small fluctuations are part of seasonal cycles or variations in moisture.