The goal of this project is to develop a new carbon dioxide injection enhanced oil recovery (CO2-EOR) process using engineered nanoparticles with optimized surface coatings that has better volumetric sweep efficiency and a wider application range than conventional CO2-EOR processes. The objectives are to (1) identify the characteristics of the optimal nanoparticles that generate extremely stable CO2 foams in situ in reservoir regions without oil; (2) develop a novel method of mobility control using “self-guiding” foams with smart nanoparticles; and (3) extend the applicability of the new method to reservoirs having a wide range of salinity, temperatures, and heterogeneity.
The University of Texas at Austin, Austin, Texas 78712-0228
Although EOR with CO2 is practiced domestically on large scale, the potential for expansion is enormous. The single greatest obstacle to fully realizing that potential is the inherently poor volumetric sweep efficiency of the process. The very low viscosity of CO2 and its relatively low density lead to severe channeling and segregation by gravity override. Most of the CO2 EOR projects in the U.S. are in carbonate reservoirs, which tend to have high-permeability layers or networks of very high permeability fractures. High CO2 mobility within these portions of the reservoirs results in very low sweep efficiencies.
While the water-alternating-gas (WAG) process is commonly used to provide modest conformance control, the ongoing search for better solutions has motivated extensive research on the use of surfactant-stabilized CO2 foams. The formation of CO2-in-water foams lowers the CO2 mobility resulting in improved sweep efficiency.
While ongoing research on surfactants is likely to lead to improved foam performance, alternative solutions are also valuable for large numbers of fields where current technology has not provided economical sweep efficiencies. The solution to be pursued in this project is to continue to use foam—it is clearly effective for increasing CO2 sweep efficiency—and to stabilize it by a different mechanism. Nanoparticles are currently of great interest for their ability to form emulsions and foams because of their robust chemical stability (even in harsh reservoir conditions) and extremely strong and selective adsorption at targeted fluid/fluid interfaces. Their surface coating can be tailored to favor CO2/water foam without forming oil/water emulsions. The foams are formed in high permeability zones where the shear rate reaches a threshold to generate foam. These properties raise the possibility of creating "self-guiding" fluids that selectively reduce CO2 mobility by generating foam only in regions where CO2 is flowing rapidly, such as fractures and gravity override regions that contain little oil. The same foam breaks in the presence of resident oil to enable high recovery by contact with the now mobile CO2.
Engineered nanoparticle-stabilized foam has "game-changing" potential to remedy several difficulties with current technologies for improving volumetric sweep efficiency of CO2 floods, thus increasing domestic oil production. One impact may be the expanded application of CO2-EOR processes to oil reservoirs previously considered uneconomic or not suitable for CO2 flooding. Furthermore, the low cost of engineered nanoparticles and their potential to provide improvement in sweep efficiency for a wide range of reservoirs can lead to greatly improved economics for CO2-EOR.
The successful use of nanoparticles for advanced CO2-EOR processes also has the potential to lead to additional new generation EOR processes because the nanoparticles can carry additional functionalities such as paramagnetism, catalysis, or reaction capabilities.
Silica-based nanoparticles have been used to form CO2 foams that have apparent viscosities suitable for EOR. Foam generation by co-injection of CO2 and polyethylene glycol (PEG)-treated commercial silica nanoparticles was observed in beadpacks. Normalized apparent viscosities up to 16 cP were observed for low concentration (3.00 wt. percent) nanoparticle dispersions and were at a maximum when CO2 density was highest.
Commercially-produced Wacker fumed silica particles with 50 percent dichlorodimethylsilane surface modification were designed to stabilize CO2 foams and showed high stability, with less than 10 percent foam resolution (by height) in 24 hours. The foams were composed of bubbles smaller than 100 micrometer (μm) as a result of high adsorption energy, which contributed to the high stability.
Researchers discovered that fly ash contains a component that is remarkably effective at stabilizing emulsions and foams. The capability to test foam generation in rough-walled fractures has been developed.
A “platform particle” synthesis strategy was developed to streamline the testing of nanoparticle efficacy for foam stabilization. The combinatorial materials chemistry approach (platform particles) in which polymers are adsorbed on “standard” nanoparticle cores to control their surface properties enables simultaneous testing of multiple polymers on the same nanoparticles of optimal size. This high-throughput approach is applied to find particle coatings with optimal activity at the CO2-water interface.
Researchers demonstrated the stability of nanoparticles coated with PEG (which are very effective at generating foam) in high salinity (100,000 ppm) aqueous brine solutions at up to 60° C.
Very high foam viscosities (~60 cP) with surface-modified nanoparticles using inexpensive fumed silica as the core were achieved.
Foam was generated by co-injecting liquid CO2 (ambient temperature, 1800 psia) and an aqueous dispersion of PEG-coated silica nanoparticles from 3M through a fractured sandstone core. The effective fracture aperture was 40 microns. The viscosity of the mixture of foam, CO2 , and brine ranged from two to five times greaterlarger than the viscosity of the fluids without nanoparticles, depending on the proportions of CO2 and brine. This is the first demonstration that foam can be generated by co-injection in a key geometry relevant to field operations, namely, within a fracture.
The project has been completed and the final report is available below under "Additional Information".
Final Project Report [PDF-5.42MB]
CO2 EOR: Nanotechnology for Mobility Control Studied [PDF-1.65MB] - News Release July, 2012