**4. Conclusion**

Despite of over five decades of extensive work in developing and identifying viable gas thickeners for EOR applications such as fluorous and non-fluorous polymers, copolymers, and low molecular weight compounds, so far none of these materials may be considered effective thickeners for field applications [6]. In fact, the design of affordable thickeners for CO2 or HC gases effective at low concentrations (i.e. <1 wt%) is highly challenging due the low solubility of the additives in these solvents.

The main conclusions derived from this review are as follows:


*Direct Gas Thickener DOI: http://dx.doi.org/10.5772/intechopen.88083*

*Enhanced Oil Recovery Processes - New Technologies*

and environmental concerns.

Despite of over five decades of extensive work in developing and identifying viable gas thickeners for EOR applications such as fluorous and non-fluorous polymers, copolymers, and low molecular weight compounds, so far none of these materials may be considered effective thickeners for field applications [6]. In fact, the design of affordable thickeners for CO2 or HC gases effective at low concentrations (i.e. <1 wt%) is highly challenging due the low solubility of the additives in

• At laboratory scale, the best CO2 thickeners are PDMS, P-1-D, polyFAST, and PFOA for CO2 mobility and conformance control. However, the use of these materials for field applications is not sustainable due to their elevated manufacturing costs, the large concentrations required to ensure technical success,

• There are several small-molecule compounds that have been identified as CO2 thickeners including semi-fluorinated trialkyltin fluorides, fluorinated bis-ureas, di-chain perfluorinated sulphosuccinate surfactants, and branched benzene trisurea. In general, these compounds are capable of increasing the CO2 viscosity between 1.5- and 300-fold at lower temperatures (298–313 K). However, most of these materials are fluorinated and can improve the viscosity only at high concentrations (2–10 wt%). In addition, the intermolecular associations displayed by these compounds are effective at low temperatures; therefore, they cannot be used at typical reservoir conditions due to the dimin-

• Effective polymer thickeners for NGL components include DRA polymers, PDMS, and PAO oligomers. These polymers are much more effective for thickening butane and less effective for propane and ethane. DRA polymers are promising thickeners (3–23-fold) at dilute concentrations over temperatures of 298–333 K, while PDMS and PAO show moderate viscosity enhancements (1.2–5-fold) over the same temperatures. In addition, P-1-D seems to be a suit-

• Small-molecule compounds such as TBTF, HAD2EH, and CPE are effective thickeners for pure light alkane components at moderate temperatures (313– 333 K). Nevertheless, phase behaviour and environmental issues (fluorine

The main conclusions derived from this review are as follows:

ishing intermolecular associations at high temperature [2].

able thickener in an AG mixture at temperatures above 373 K.

content) prevent the use of these materials for EOR applications.

**4. Conclusion**

these solvents.

**84**
