Potential and Challenges of Foam-Assisted CO2 Sequestration

Abstract

Foam is a promising means to assist in the permanent, safe subsurface sequestration of CO2, whether in aquifers or as part of an enhanced-oil-recovery (EOR) process. Here we review the advantages demonstrated for foam that would assist CO2 sequestration, in particular sweep efficiency and residual trapping, and the challenges yet to be overcome. CO2 is trapped in porous geological layers by an impermeable overburden layer and residual trapping, dissolution into resident brine, and conversion to minerals in the pore space. Over-filling of geological traps and gravity segregation of injected CO2 can lead to excessive stress and cracking of the overburden. Maximizing storage while minimizing overburden stress in the near term depends on residual trapping in the swept zone. Therefore, we review the research and field-trial literature on CO2 foam sweep efficiency and capillary gas trapping in foam. We also review issues involved in surfactant selection for CO2 foam applications. Foam increases both sweep efficiency and residual gas saturation in the region swept. Both properties reduce gravity segregation of CO2. Among gases injected in EOR, CO2 has advantages of easier foam generation, better injectivity, and better prospects for long-distance foam propagation at low pressure gradient. In CO2 injection into aquifers, there is not the issue of destabilization of foam by contact with oil, as in EOR. In all reservoirs, surfactant-alternating-gas foam injection maximizes sweep efficiency while reducing injection pressure compared to direct foam injection. In heterogeneous formations, foam helps equalize injection over various layers. In addition, spontaneous foam generation at layer boundaries reduces gravity segregation of CO2. Challenges to foam-assisted CO2 sequestration include the following: 1) verifying the advantages indicated by laboratory research at the field scale 2) optimizing surfactant performance, while further reducing cost and adsorption if possible 3) long-term chemical stability of surfactant, and dilution of surfactant in the foam bank by flow of water. Residual gas must reside in place for decades, even if surfactant degrades or is diluted. 4) verifying whether foam can block upward flow of CO2 through overburden, either through pore pathways or microfractures. 5) optimizing injectivity and sweep efficiency in the field-design strategy. We review foam field trials for EOR and the state of the art from laboratory and modeling research on CO2 foam properties to present the prospects and challenges for foam-assisted CO2 sequestration.

Lab on a chip for a low-carbon future

“…CO 2 foams are being applied for enhanced oil recovery and there is significant interest in using foams to assist with improved subsurface sequestration. 68,69 The use of CO 2 as foam in the subsurface can control the mobility of the gas and limit the extent of fingering and gravity override. 29 Indeed, foams in microfluidic porous media have been shown to increase the volume of gas trapped in the swept zone and reduce the amount of gas entering thief zones.…”

Improved oil recovery techniques and their role in energy efficiency and reducing CO2 footprint of oil production

“…Foam can be used to improve the utilization factor of gas in EOR processes. For example, improving the utilization factor from 2 bbl/tCO 2 to 4 bbl/tCO 2 can reduce the CO 2 intensity of the produced oil from 120 kgCO 2 /bbl to 80 kgCO 2 /bbl (33% reduction) (Rossen et al, 2022).…”

CO2-Soluble Nonionic Surfactants for Enhanced CO2 Storage via In Situ Foam Generation

“…29 Rossen et al addressed challenges associated with foam-assisted CO 2 storage where the surfactant is added to the aqueous phase. 28 To the best of our knowledge, this work represents the first laboratory assessment of CO 2 -soluble surfactants to improve CO 2 storage. While previous work has demonstrated the ability of surfactants to improve CO 2 sweep efficiency, all of these studies have employed surfactants that are only soluble in the aqueous phase.…”

“…Yu examined the foaming properties of water-soluble ionic surfactants added to the brine phase in core flooding experiments at reservoir conditions to improve CO 2 storage in porous media. , Zhou et al evaluated amphoteric surfactants to enhance the stability of CO 2 -foams at reservoir conditions . Rossen et al addressed challenges associated with foam-assisted CO 2 storage where the surfactant is added to the aqueous phase …”

“…The presence of surfactants dissolved in water has been shown to improve CO 2 sweep efficiency in the context of GCS. ,− For example, Kim et al reported that a water-soluble nonionic surfactant comprised of CO 2 -philic polypropylene groups and a hydrophilic polyethylene group increased the contact angle (θ) of CO 2 on a silica surface from 20° to 70° and decreased CO 2 –water IFT . Improved sweep efficiency was demonstrated by saturating an etched glass microfluidic chip with a surfactant solution and injecting it with CO 2 .…”