Polymer flooding is the most commonly applied chemical enhanced-oil-recovery technique. This paper provides an update on the status of polymer-flooding technology, focusing more on field applications than on theoretical and laboratory research. It covers the following topics: • Mechanisms of polymer flooding • Polymers used • Polymer-solution stability • Technical screening criteria • Laboratory and simulation work • Performance-monitoring technique • Summary of pilots and large-scale applications • Experience and learning from field projects • Polymer flooding in heavy-oil reservoirs • Polymer viscoelastic properties • Problems associated with polymer flooding and their solutions • Future developments The data and analysis presented in this paper will give readers updated information describing polymer flooding, as well as a guide to the relevant research. Survey data will also provide operators with reference data for project design and optimization.

Surfactant enhanced oil recovery (EOR) includes surfactant flooding and surfactant stimulation. The main functions of surfactants are to reduce interfacial tension and wettability alteration. This paper is to review the EOR technology related to surfactant injection. The reviewed topics include the following:• Surfactant EOR mechanisms• Factors affecting interfacial tension• Trapping number• Screening criteria• Laboratory work• Numerical simulation work• Summary of pilot and large-scale applications• Surfactants used• Salinity gradient• Surfactant EOR in carbonate reservoirs• Surfactant EOR in shale reservoir

An article by Hart (2011) quoted one of EOG resources recent reports that recovery factor for the Eagle Ford shale play during primary drive reservoir depletion will be roughly 5%. The vast oil remaining stimulates our efforts to investigate the application of enhanced oil recovery methods in shale oil reservoirs. Recent numerical studies have indicated that cyclic gas injection could be an effective method to increase the oil recovery of shale oil reservoirs. Cyclic gas injection could be an effective technique because it is a single-well process; well-to-well connectivity is not required. The hydraulic fracturing provides a large contact area for the injected gas to penetrate and diffuse into the low-permeability matrix. The payback period of the cyclic gas injection process is rather short compared with that of the field- scale flooding process. This makes the single-well cyclic injection process a low-risk process. This paper presents our experimental verification and quantification of the potential of using cyclic CO₂ injection in shale oil reservoirs. This work is the first experimental work to investigate the performance of CO₂ huff-n-puff on shale cores. Core plugs of Mancos and Eagle Ford shales were used. A special lab set up was built to conduct this study. The effects of cyclic time (Soaking Period) and injection pressure on oil recovery, among other parameters, were investigated. Our experimental results showed that cyclic CO₂ injection could increase the recovery factor from 30% to 70% depending on the shale core type. It also shows the effect of the pores connectivity and heterogeneity on the performance of CO₂ huff-n-puff. This study shows that one of the important mechanisms of cyclic gas injection is the pressure effect that causes a large pressure drawdown during the production phase.