CO2 Foam Pilot in Salt Creek Field, Natrona County, WY: Phase II: Diagnostic Testing and Initial Results

In a previous paper we described the laboratory work, reservoir simulation, and initial design of a CO₂ Foam Pilot in the Salt Creek Field, Natrona County, WY. In this paper, we review the diagnostic testing and initial results from the pilot including: injection rate profile, production data analysis, injection and production logging, chemical tracers, streamline analysis, and reservoir simulation.

Although the CO₂ flood has been very successful at Salt Creek, it is recognized that certain isolated patterns have exhibited high CO₂ production and inefficient CO₂ utilization, most likely due to the channeling of fluids through high permeability, low volume zones (fractures, thief zones, etc.) and the gravity over-ride of the injected fluids. Accordingly, a foam pilot was initiated to test the ability of CO₂ to remediate these conditions.

A change in the injection well rate (at constant surface injection pressure) was the first indicator to be observed; the injection rate decreased by approximately 40%, indicating a strong mobility reduction of the CO₂ in the reservoir. Production and injection profile logs were run before and after surfactant injection, and a change in profile was observed in one producer. Chemical tracers were injected in both the gas and water phases before and after surfactant injection; results indicate that CO₂ was diverted from high permeability, low volume conduits, such as fractures. An analysis of the production data for the four offset producers show a definite increase in liquid production and a corresponding decrease in GLR (gas-liquid-ratio.) Streamline analysis suggest areal diversion of CO₂ over time. Finally, reservoir simulation prediction cases are given and discussed.

CO₂ flooding has become a standard EOR technique for many water-flooded fields. Methods for increasing the efficiency of these floods, such as the use of CO₂ foam, can add great value.