Shivana R. Samuel, SPE, Ergun Kuru, SPE, Japan J Trivedi, SPE, University of
SPE Improved Oil Recovery Symposium,
14-18 April 2012,
Tulsa, Oklahoma, USA
|6.4 Primary and Enhanced Recovery Processes
6.4.6 Chemical Flooding Methods Methods (e.g., Polymer, Solvent, Nitrogen, Immiscible CO2, Surfactant, Vapex)
6.4.2 Gas-Injection Methods
6.3.1 Flow in Porous Media
6.3.3 Conformance Improvement
The problems associated with current chemical flooding technologies are based
around inadequate sweep efficiencies and unfavorable mobility ratios which
leave much of the recoverable oil left untouched in the pores of the reservoir.
In order to address the low sweep efficiency and unfavorable mobility ratio
issues, numerous formulations of polymer and surfactant base fluids have been
used for enhanced oil recovery (EOR) applications with varying degree of
success. The use of Colloidal Gas Aphrons (CGA) as an alternative chemical EOR
technique is investigated in this study. Colloidal Gas Aphrons (CGA) are
described as micro-bubbles which are 10 to 100 microns in size with a gas
containing inner core encapsulated by a thin surfactant film. Aqueous CGA
fluids are comprised of water, polymer and surfactant solutions.
An experimental study was conducted to determine the optimum surfactant and
polymer concentrations which would yield stable micro-bubbles. The formulations
of stable micro-bubbles were analyzed in terms of rheology, bubble size
distribution and time stability.
In order to determine the displacement efficiency of CGA fluid in the EOR
process, flooding experiments were conducted using a 2D linear model and 3D
radial model, both packed with glass beads and saturated with mineral oil.
Flooding experiments were performed using a) water, b) aqueous polymer
solution, c) aqueous polymer and surfactant solution mixed at low shear rate,
d) CGA fluid, e) water followed by CGA fluid, and f) water followed by polymer
Efficiency of oil recovery using the CGA fluid was compared to that of other
fluids. All experiments were repeated to ensure consistent results. Less than 3
% variation in results was observed in all cases.
Pressure drop, ultimate recovery and injected fluid retention time data were
measured during the flooding experiments. In addition, time-lapse images taken
at regular intervals were analyzed to study frontal displacement patterns
observed in 2-D experiments.
The results indicated that the CGA fluids showed more stable frontal
displacement as compared to water flooding. The cumulative oil recovery
performance of CGA fluids was comparable but slightly less than that of aqueous
polymer solutions. CGA fluids, however, required significantly lower injection
pressure as compared to aqueous polymer solutions. The breakthrough time of CGA
fluids was longer than that of any of the other fluids tested indicating that
CGAs have longer retention time.
Results from preliminary experiments encourage the further investigation of
colloidal gas aphrons as an alternative EOR technique. The results will also be
useful in designing an EOR process as an alternate to polymer,
surfactant-polymer or WAG flood with particular importance to carbon
sequestration as CO2 / flue gas can also be used in micro-bubble generation in
place of air.
Aphrons were first described by Sebba (1987) who later introduced the term
Colloidal Gas Aphron (CGA). Colloidal gas aphrons are micron sized bubbles
composed of a gaseous inner core encapsulated by an inner and outer surfactant
layer. Between these surfactant layers there is viscous water layer which is
important to aphron stability. Figure 1 shows the structure of an aqueous
colloidal gas aphron. CGA are termed aqueous when they are dispersed in an
aqueous surfactant solution.