Carbon capture, utilization and storage

By Scott M. Smouse

Fossil fuels will remain the predominant source of global energy through for at least the next two decades and possibly beyond. However, their usage will continue to produce carbon dioxide (CO2). Many studies evaluating mitigation options argue that carbon capture is an essential technology that should be applied to any carbon-based fuel, including coal, natural gas, and biomass.

For years, organizations around the world, such as the U.S. Department of Energy’s National Energy Technology Laboratory, have been researching and developing technologies to lessen the impacts of fossil fuel utilization. Among the portfolio of options being explored, beneficial reuse and consumption of CO2 has lately been receiving increased emphasis. These applications consist of processes, technologies, or applications that generate valuable chemicals, fuels, raw materials, or have considerable environmental or economic advantages over the status quo.

Although long viewed as an attractive concept, most assessments have not found adequate beneficial uses for CO2 on the scale of their anthropogenic emissions, which has resulted in a focus on large-scale capture and geologic storage. However, according to the International Energy Agency (IEA), utilization has the potential to reduce CO2 emissions by at least 3.7 gigatons per year, or about 10 percent of the world’s current annual emissions. Finding beneficial uses has received increased attention as a tool for achieving reductions of anthropogenic CO2 and as a means to initiate deployment of this technology absent specific regulatory mandates.

Some utilization technologies, such as CO2-enhanced oil recovery (CO2–EOR), are already proven and viable. For example, there are about 114 active commercial CO2 injection projects in the United States, the world leader in CO2–EOR, that together inject over 2 billion cubic feet of CO2, mostly from natural reservoirs, to produce over 280,000 barrels of oil per day (Oil and Gas Journal, April 19, 2010). Other specific applications for CO2-enhanced hydrocarbon recovery include enhanced coal bed methane production (ECBM), enhanced gas recovery (EGR), enhanced gas hydrate recovery (EGHR), hydrocarbon recovery from oil shale, and the fracturing of reservoirs to increase oil/gas recovery. The common characteristics of CO2-enhanced hydrocarbon recovery processes include:

· Recovery of conventional and unconventional hydrocarbon resources (oil, conventional gas, shale gas, coal bed methane, oil shale, and tar sands),
· Recycling, or once-through use of CO2 in conjunction with hydrocarbon recovery,
· The need for high-pressure CO2 and/or appropriate surface infrastructure, such as wells, compressors, and pipelines. CO2 purity required for each application may vary depending on the specific application.

Other utilization technologies are at various stages of development, but show promise, including production of chemical feedstocks and conversion to fuels, plastics, minerals, and cement. The use of CO2 in various applications may have economic and/or environmental benefits by providing a value to the end-user, which creates a market for CO2 producers. Historically, the market for CO2 has been relatively small compared to anthropogenic emissions. However, there is an impetus to explore additional uses to mitigate CO2 emissions. Using CO2 for beneficial purposes can be perceived as being more valuable (e.g., hydrocarbon resource recovery) or having a lower risk (e.g., applications where CO2 is consumed) compared to geologic storage. These views may lead to the development of extensive CO2 pipeline networks, which, in turn, will enhance longer-term prospects for geologic CCS. For example, additional CO2 available to a CO2–EOR project may be injected into a saline formation near the oil reservoir, thereby reducing the need for additional infrastructure (such as wells and pipelines) for larger-scale, long-term injection.

It is essential to apply sound analytic methodologies to assess both the potential represented by any beneficial use concept and to estimate the full range of benefits, in terms of the net CO2 emissions, the duration of such storage (if it is not consumed), the potential market value of a use, and finally, the net energetic impact. Some considerations in establishing these metrics include:

· Total amount of CO2 permanently sequestered
· Unit value (benefit) or cost of application
· Energy consumed by the application (or net-CO2 savings from the technology)
· Market potential of primary CO2 use and any by-products

The beneficial uses of CO2 are worthy of continued research, development, and demonstration. No single process will mitigate all anthropogenic CO2; however, with the continued R&D, the number of applications is increasing. The U.S. Department of Energy’s R&D program is researching novel techniques that could significantly improve the economic performance and expand the applicability of CO2 injection to a broader group of oil reservoirs. With the proper incentives, these technologies could lead to large-scale commercial applications, which would jump-start development of the infrastructure needed to manage large amounts of captured CO2 and to lessen the total social costs. Some approaches for geologic storage and utilization may be synergistic, which could lead to significant benefits.