The goal of this project is to develop and evaluate, through coreflood tests at reservoir conditions, a nanoparticle-stabilized carbon dioxide (CO2) foam system that can improve CO2 sweep efficiency in CO2 enhanced oil recovery (EOR) and minimize particle retention in the reservoir.
New Mexico Institute of Mining and Technology/Petroleum Recovery Research Center, Socorro, NM 87801-4681
Improving oil production is becoming more crucial as worldwide oil demand rapidly increases, and the development of new technology is needed to fulfill this demand. In particular, EOR with CO2 is regarded as a promising technology to not only improve oil production, but also to mitigate carbon emissions through their capture and storage in deep geologic formations. A revised national resource assessment for CO2-EOR (July 2011) prepared for DOE by Advanced Resources International indicated that “Next Generation” CO2-EOR can provide 137 billion barrels of additional technically recoverable domestic oil, with about half (67 billion barrels) economically recoverable at an oil price of $85 per barrel. However, CO2 flooding processes frequently experience poor sweep efficiency despite the favorable characteristics CO2 has for achieving dynamic miscibility with oil under most reservoir conditions. Because the mobility of CO2 is high compared to that of oil, channeling that initially results from reservoir heterogeneity can be further increased, thus strengthening the need for mobility control during CO2 flooding.
Research results have demonstrated that surfactant-induced CO2 foam is an effective method for mobility control in CO2 foam flooding. However, surfactant-stabilized CO2 foams have some potential weaknesses. Because the foam is by nature ultimately unstable, its long-term stability during a field application is difficult to maintain. This is especially true when the foam contacts the resident oil. Under high-temperature reservoir conditions, surfactants generally tend to degrade before they fulfill their long-term function. In addition, surfactant loss in a reservoir due to adsorption in porous media results in a large consumption of chemicals and is a major factor governing the economic viability of CO2 foam flooding.
New nano-science technologies may provide an alternative for the generation of stable CO2 foam. It is known that small solid particles can adsorb at fluid/fluid interfaces to stabilize drops in emulsions and bubbles in foams. The solid-stabilized dispersions may stay stable for years upon storage. The use of nanoparticles instead of surfactant to stabilize CO2 foam may overcome the long-term instability and surfactant adsorption loss issues that affect surfactant-based CO2-EOR processes. The high adhesion energy of the particles enables adsorption and is essentially irreversible, thus solid nanoparticles strongly and preferentially adsorb to either the water or gas phase at the water/CO2 interface and create a protective barrier around each dispersed bubble of gas (if the nanoparticle is hydrophilic) or drop of water (if the nanoparticle is hydrophobic) to produce highly stable and durable foam. These properties imply that long-term stabilization of nanoparticle-stabilized CO2 foam may be obtained.
Successful results of the planned experiments, together with the development of the nanoparticle-stabilized CO2 foam and an evaluation of its potential for field testing, will benefit the oil industry in its enhanced recovery efforts. Nanoparticles are solid and can withstand harsh environments and high temperatures; thus, a successful project will extend the benefits of CO2 flooding to those high-temperature reservoirs in which surfactant-stabilized CO2 foam cannot survive. A successful project will provide an alternative CO2-EOR technology that may drastically reduce the costs of a CO2-EOR operation and, in addition, provide promising economic benefits from further oil recovery.
Silica nanoparticles easily passed through the sandstone core without changing its permeability. Little adsorption was observed as nanosilica particles flooded the limestone core and core permeability remained unchanged. Core plugging did occur and core permeability was changed with injection of nanoparticles into a dolomite core.
Very stable and uniform CO2 foam was generated when liquid CO2 and nanosilica dispersion flowed through a sandstone core sample. CO2 foam could be generated at a nanosilica concentration as low as 500 ppm. Increasing nanosilica concentration reduced foam mobility and increased the foam resistance factor. The CO2 foam mobility remained almost constant as the foam quality increased from 20 to 60 percent; however, an additional increase in foam quality from 60 to 90 percent increased CO2 foam mobility. CO2 foam mobility decreased with an increase in total flow rate and increased with an increase in core permeability.
The research also demonstrated that the addition of a small amount (30–50 ppm) of surfactant to a nanoparticle solution significantly improved CO2 foam generation and foam stability.
Nanoparticle-stabilized CO2 foam was observed to improve the residual oil recovery in sandstone, limestone, and dolomite cores. The residual oil saturation decreased from 39.2 percent (after water flooding) to 9.95 percent after 5 pore volumes of nanosilica and CO2 were injected in the sandstone core. For limestone and dolomite cores, the CO2/nanosilica dispersion recovered 33.2 and 26.5 percent of residual oil, respectively.
A long-term coreflooding test of nanoparticle-stabilized CO2 foam for residual oil recovery indicated that after 20 PV of CO2/nanosilica dispersion were injected into the core, total nanoparticle recovery during CO2/nanosilica dispersion flooding was ~95.3 percent. No significant core permeability change was observed, indicating no particle plugging occurred during the long-term coreflooding. Small volume (1 PV) CO2/nanosilica dispersion coreflooding tests showed that ~32 percent of residual oil was recovered as 1 PV CO2/nanosilica dispersion was flooded into the core.
The project has been completed and the final report is available below under "Additional Information".
Final Project Report [PDF-41.7MB]
CO2 EOR: Nanotechnology for Mobility Control Studied [PDF-1.65MB] - News Release July, 2012