Foam assisted CO 2 enhanced oil recovery has attracted increasing attention of oil companies (operators and service companies) and research institutions mainly due to the potentially high benefit of foam on CO 2 -EOR. Miscible and immiscible CO 2 flooding projects are respectively proven and potential EOR methods. Both methods have suffered from limited efficiency due to gravity segregation, gas override, viscous fingering and channeling through high permeability streaks. Numerous theoretical and experimental studies as well as field applications have indicated that foaming of CO 2 reduces its mobility, thereby helping to control the above negative effects. However, there are still various conceptual and operational challenges, which may compromise the success and application of foam assisted CO 2 -EOR. This paper presents a critical survey of the foam assisted CO 2 -EOR process to reveal its strengths, highlight knowledge gaps and suggest ways. The oil recovery mechanisms involved in CO 2 foam flood, the effect of gaseous and soluble CO 2 on the process, synergic effect of foaming agent and ultra-low IFT surfactants, logistic and operational concerns, etc. were identified as among the main challenges for this process. Moreover, the complex flow behaviour of CO 2 , oil, micro-emulsion and brine system dictates a detailed study of the physical-chemical aspects of CO 2 foam flow for a successful design. Unavailability of reliable predictive tools due to the less understood concepts and phenomena adds more challenges to the process results and application justifications. The study highlights the recent achievements and analysis about foam application and different parameters, which cannot be avoided for a successful foam assisted CO 2 flood design and implementation. Accordingly, the study also addresses prospects and suggests necessary guidelines to be considered for the success of CO 2 foam projects. SPE 165280sweep efficiency in CO 2 -floods can be high, and the displacement efficiency of a miscible CO 2 flood often exceeds 90%. However, the sweep efficiency of CO 2 processes is often poor. Limitations of the current CO 2 -EORCO 2 would be much more widely used if it were abundantly available (Orr Jr., 2003). Natural sources, by-product of gas treatment units, and combustion processes could be supply sources of CO 2 . However, the present technologies of CO 2 capture and pressurization require energy which would result in a decreased overall energy efficiency and added cost. To recover additional oil in a CO 2 -EOR process, CO 2 is generally injected into the reservoir as a supercritical fluid (Sc-CO 2 ). Sc-CO 2 viscosity is lower than water and most crude oils, which can lead to a number of conformance and mobility issues, and instability in the displacement front, as shown in Fig. 1. Due to the adverse mobility ratio, fingers of CO 2 grow from the displacement front, and cause premature breakthrough, and inefficient CO 2 utilization. Furthermore, the tendency of lower density CO 2 to migrate toward the upper p...
Foam is used in CO2-enhanced oil recovery due to its potential high benefits in mitigating all three causes of CO2 poor sweep efficiency, as it provides a means to lower the effect of permeability heterogeneity, overcome viscous instability, and minimize the occurrence of gravity override. The conventional foaming surfactants are not suitable in contact with oil due to premature lamellae rupture, need for copious amounts of water to generate foam, surfactant loss due to adsorption on the rock or partitioning between water and oil, and less tolerance against salinity, pressure, and temperature. The surfactant blending and addition of CO2-philic functionalities in surfactant structure are suggested to mitigate the above problems, enhance foam stability, improve mobility control, and accelerate foam propagation. However, there is a lack of general guidelines on the evaluation of CO2-philic surfactant properties and applications and the surfactant structure–performance analysis. In the present work, tailor-made laboratory tests and simulation analysis were conducted on CO2-philic surfactants with different structures and chain lengths in conditions close to a Malaysian reservoir case and in the presence of oil. The results from experiments combined with analytical analysis of foam flow parameters are used to provide a comprehensive simulation model of a CO2-philic surfactant alternating gas process. A meaningful correlation between the CO2-philic surfactant structure and the sensitivity of foam model to different parameters was observed. On the basis of sensitivity analysis results, optimization of CO2-philic surfactant activity at gas–water and oil–water interfaces can improve the system recovery through macroscopic and microscopic displacement.
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