Geochemical monitoring of fluid-rock interaction and carbon dioxide storage at the Weyburn carbon dioxide injection enhanced oil recovery site, Saskatchewan.

摘要

The Weyburn Oil Field, Saskatchewan, Canada, is the site of a large CO 2 injection enhanced oil recovery project. After ten years of primary production, and thirty-six years of waterflooding, PanCanadian (now EnCana) began CO2 injection into the Midale formation in October 2000. The multidisciplinary International Energy Agency (IEA) led Weybum CO 2-Enhanced Oil Recovery Monitoring program took this opportunity to study the potential for the geologic storage of CO2 of which geochemical monitoring and modeling plays an important role.; In this thesis, pre-injection (Baseline) and post-injection (Monitor-1) samples of produced fluids were sampled and chemically analyzed to establish the geochemical and isotopic processes existing prior to and as a result of CO2 injection. The dominant processes controlling the Baseline fluid distribution include bacterial sulfate reduction and the mixing of low salinity water from the northwest of the study area and high salinity water from the southeast. After CO2 injection, the general spatial distributions of the fluid chemistry were similar, but the pH dropped and HCO3, Ca, Mg and delta13C of CO2 values increased, suggesting carbonate dissolution.; Addition of CO2 causes dissolution of carbonate minerals and production of HCO3 until equilibrium with the carbonate minerals is obtained. CO2 can be trapped on a geologic time scale in the form of bicarbonate or carbonate minerals if silicate minerals are present which are capable of buffering the pH. Modeling of water rock reaction suggests that reservoir fluids may be reacting with trace amounts of silicate minerals capable of buffering pH, and thus trapping CO2.