Immiscible CO2 Flooding for Increased Oil Recovery and Reduced Emissions

Abstract

Abstract Carbon dioxide is both the most-recognized greenhouse gas as well as the second most-used injectant in oil fields, after water. This coincidence creates the possibility of injecting previously-vented CO2 to both reduce greenhouse gas emissions and increase oil recovery. Such a project has been evaluated for the Avile reservoir of the Puesto Hernandez field, located in the Neuquen Basin in west-central Argentina. This oil field produces associated gas containing approximately 60 percent CO2, which has previously been vented. The project described below assessed the feasibility of extracting and injecting the CO2 into the field to recover additional oil using an immiscible displacement process. Following an evaluation including core floods, compositional simulation, and facilities evaluation, the process was found both to have technical and economic promise in terms of improved oil recovery, and to result in reduction of both CO2 and methane emissions, the latter being an especially potent greenhouse gas. The success of this type of project would create a unique common ground for those concerned with reducing global warming and those concerned with supplying society's energy needs. Introduction This project evaluated the application of a seldom-used process (immiscible CO2 flooding) in the Avile reservoir of the Puesto Hernandez field, located in the Neuquen Basin in west-central Argentina (see Figure 1), a region with no prior history of CO2 injection. Therefore, all aspects of a gas injection project had to be investigated to arrive at a best estimate of whether the project made technical and economic sense. Described below are the properties of the Avile Reservoir, Puesto Hernandez Field, Argentina; results of the laboratory fluid characterizations and core floods; pilot area compositional simulations and the resulting incremental oil rate projections; the analysis of facility requirements; the impact of this project on greenhouse gas emissions; and the estimated economic viability of the project. Significant tertiary oil recovery potential exists based on laboratory studies of fluids and core materials from the reservoir combined with compositional simulation of the laboratory experiments and a field pilot model. Using a conservative interpretation of the available laboratory core flood data resulted in favorable project economics under base assumptions, with a low likelihood of negative economic returns. The project was estimated to incrementally recover approximately 4.0 percent of the original oil in place, corresponding to 220,000 Sm3 for the pilot area and 670,000 Sm3 for the combined pilot and full project expansion. The potential greenhouse gas emission reductions range from approximately 185,000 carbon equivalent metric tons for the pilot to 714,000 carbon equivalent metric tons for the combined pilot and full project expansion. Discussion Reservoir Characteristics. Comprised dominantly of aeolian sand dune deposits, the Avile Reservoir in the Puesto Hernandez Field can be characterized as a monotonous, massive sandstone. Vertical variations in porosity are often subtle and may have limited lateral continuity (see Figure 2). For the purpose of this study, the Avile was sub-divided into a total of eight layers. These eight flow units reflected the maximum number of vertical divisions that have reasonable lateral correlation. Each layer top was picked at the top of a relatively high porosity bed with the shallower reduced porosity thickness assigned to the layer above. The lower portion of the Avile (layers 5–8 in this study) had more consistent thickness, while the upper Avile (layers 1–4 in this study) was more variable. Reservoir Characteristics. Comprised dominantly of aeolian sand dune deposits, the Avile Reservoir in the Puesto Hernandez Field can be characterized as a monotonous, massive sandstone. Vertical variations in porosity are often subtle and may have limited lateral continuity (see Figure 2). For the purpose of this study, the Avile was sub-divided into a total of eight layers. These eight flow units reflected the maximum number of vertical divisions that have reasonable lateral correlation. Each layer top was picked at the top of a relatively high porosity bed with the shallower reduced porosity thickness assigned to the layer above. The lower portion of the Avile (layers 5–8 in this study) had more consistent thickness, while the upper Avile (layers 1–4 in this study) was more variable.