ABSTRACT

The CO₂ tertiary oil recovery project is designed to recover additional reserves and evaluate the efficiency of the recovery process. The project consists of ten miscible CO₂ floods using both the push-pull and single well huff-puff processes. Geological reservoir characterization and modeling were performed to aid in design of the floods and to quantify the reservoir risk.

Various techniques were used to evaluate the floods including deterministic modeling, geostatistical methods, seismic attribute analysis and inversion derived porosity analysis. The final work flow incorporated structural interpretation from a recently shot 3-D seismic survey and well data modeled with Landmark Stratamodel software used to build the geocellular reservoir model. The resulting geocellular model was input as the framework in the compositional fluid flow simulation model. The models were used for final project design, risk analysis, forecasted performance, and comparison to actual performance.

One of the problems encountered was a lack of uniqueness in results from the production and geologic modeling in determining reservoir continuity and, therefore, the ability to insure connectivity of all of the injectors and producers. The example geologic reservoir modeling highlighted two areas of concern: 1) The potential for a non-sealing fault between two segments, and 2) The possibility that one end of the reservoir could be partially stratigraphically separated thereby reducing the CO₂ sweep efficiency. The economics of this type of CO₂ flood is significantly affected by the amount of residual oil contacted by the CO₂. As a result, the flood was redesigned to reduce the risk of drilling or reworking unneeded wells and to enhance the economic viability of the flood.