DE-FE0005979

Goal
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.

Performer
New Mexico Institute of Mining and Technology/Petroleum Recovery Research Center, Socorro, NM 87801-4681

Background
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 not only to 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 by Advanced Resources International for DOE 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, the need for mobility control during CO₂ flooding is highly desired.

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. Even though some high-cost, specialty surfactants are available, 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 for 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.

Impact
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.

Accomplishments
Stable CO₂ foams were generated at reservoir conditions for nanoparticle concentration in the 4,000 ppm–6,000 ppm range. The effects of different factors such as particle concentration, brine salinity, pressure, and temperature on CO₂ foam generation were investigated. Adding a small amount (30-50 ppm) of surfactant to nanoparticle solution significantly improved CO₂ foam generation and foam stability. CO₂ foam generated as supercritical CO₂ and nanosilica mixture were flowed through sandstone and limestone cores, an industry first.. The apparent viscosity of the mixture with nanoparticles in the dispersion was 1.5 to 6.1 times higher than that without nanoparticles in the dispersion.

Current Status (December 2011)
CO₂ foam generation at dynamic conditions and nanosilica particle-stabilized CO₂ foam transportation across porous media is being investigated. Foam texture will be identified from a sapphire observation cell as the CO₂ and silica nanoparticle mixture flow through a porous media. The mobility of the foam is being estimated by the pressure drop across the porous media. Particle concentration, phase ratio between CO₂ and nanoparticle solution, and flow rate effects on CO₂ foam generation and foam mobility in the porous media are being investigated. Oil-free coreflooding experiments to investigate nanoparticle transportation in sandstone, limestone, and dolomite are also being performed. Particle retention in the core samples is being estimated.

Further research will investigate nanoparticle-stabilized CO₂ foam transport in core samples. Foam mobility will be estimated as the CO₂ and nanoparticle mixture flows through the core sample. Retention of the nanoparticles in the core sample will be calculated. In addition, CO₂ coreflooding experiments using nanoparticles as foam stabilizers for residual oil recovery will be initiated under reservoir conditions.

Project Start: October 1, 2010
Project End: January 31, 2014

DOE Contribution: $772,934
Performer Contribution: $385,888

Contact Information:
NETL – Sinisha (Jay) Jikich (sinisha.jikich@netl.doe.gov or 304-285-4320)
NMIMT/PRRC - Ning Liu (ningliu@prrc.nmt.edu or 5750835-5739)
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