No abstract

The economics of a steamflood project are largely dependent upon the rates at which steam is injected and oil is recovered. One of the dominant features of the steam drive process is the tendency of steam to override the reservoir and break through in the producing wells. To accommodate this situation, engineers are challenged to achieve the balance between production of heated oil and by-passed steam. A significant effort is being made to overcome this difficulty with the aid of a by-product gas tracer, carbon dioxide. The isotopic signatures of this non-condensable gas can be used to predict the changes in reservoir dynamics resulting from the reaction of reservoir rock and fluids with injected steam. Steam-enhanced oil recovery often produces large quantities of CO2. Two primary sources are oil derived CO2 and CO2 associated with injected steam. These two distinct sources can be differentiated by the carbon isotopic composition of the CO2. The CO2 generated from oil tends to be depleted in the heavy isotope of carbon, 13C, while water-derived CO2 is enriched in 13C. Results of isotope analyses of CO2 from the Cymric field steamflood show that CO2 in good flood response wells is primarily derived from oil and CO2 in steam breakthrough wells is mainly water/mineral derived. These results suggest that carbon isotopes of CO2 are useful natural tracers for its origin and may be used as a diagnostic and possibly predictive reservoir management tool for monitoring steamflood performance.