Improvement of sweep efficiency and mobility control in gas flooding

The application of carbon dioxide or other gases to extract crude oil from depleted reservoirs has been shown to be a technically successful process. However, optimized recoveries are often compromised by poor sweep efficiencies because of low gas viscosities and densities. A new process was investigated that potentially could improve sweep efficiencies by enhancing extractability properties of the injected gas with entrainers. Use of a capillary viscometer to evaluate enhanced viscosities appeared to be the best procedure for evaluating candidate compounds. A mathematical treatment was proposed based on predicting entrainer solubilities and minimum miscibility pressure alterations for carbon dioxide. However, use of many assumptions and approximations limited the effectiveness of this approach to qualitative evaluations. Some 87 compounds were evaluated using this mathematical treatment, and certain monoaromatic compounds were identified for further laboratory testing. 33 refs., 8 figs., 3 tabs.