Geochemical monitoring of fluid-rock interaction and CO 2 storage at the Weyburn CO 2-injection enhanced oil recovery site, Saskatchewan, Canada

Abstract

The Weyburn Oil Field, Saskatchewan is the site of a large (5000 tonnes/day of CO 2) CO 2-EOR injection project By EnCana Corporation. Pre- and post-injection samples (Baseline and Monitor-1, respectively) of produced fluids from approximately 45 vertical wells were taken and chemically analyzed to determine changes in the fluid chemistry and isotope composition between August 2000 and March 2001. After 6 months of CO 2 injection, geochemical parameters including pH, [HCO 3], [Ca], [Mg], and δ 13CO 2(g) point to areas in which injected CO 2 dissolution and reservoir carbonate mineral dissolution have occurred. Pre-injection fluid compositions suggest that the reservoir brine in the injection area may be capable of storing as much as 100 million tonnes of dissolved CO 2. Modeling of water-rock reactions show that clay minerals and feldspar, although volumetrically insignificant, may be capable of acting as pH buffers, allowing injected CO 2 to be stored as bicarbonate in the formation water or as newly precipitated carbonate minerals, given favorable reaction kinetics.