By John Kemp
LONDON, May 3 (Reuters) - North America has enough underground capacity in depleted oil and gas fields, uneconomic coal seams, and saline aquifers to store all its carbon dioxide emissions for the next 600 years. That is according to the first comprehensive survey published by the U.S. Department of Energy, Natural Resources Canada and Mexico's Energy Ministry.
For policymakers in all three countries, underground storage is essential if North America is to continue to burn its abundant fossil fuel reserves, especially coal, to meet energy demand without worsening climate change.
The optimistic message of the new "North American Carbon Storage Atlas," published on May 1, is that the total carbon dioxide (CO2) storage capacity of the United States is 1.8-20.4 trillion tonnes, compared with annual emissions of just 3 billion tonnes, enough to last for hundreds if not thousands of years ().
The atlas puts Canada's potential storage at 48-320 billion tonnes, compared with annual emissions of 219 million, while Mexico's resource is at least 100 billion tonnes compared with yearly emissions of 205 million, which is more than ample.
Sedimentary basins containing oil, gas and coal are also the most suitable for injecting CO2 underground in the form of a liquid or supercritical fluid (which behaves like a combination of a gas and a liquid).
The most likely areas for implementing carbon capture and storage (CCS) projects therefore overlap with states and provinces that are home to the coal mining and petroleum industries, which should ease political opposition.
Large-scale CO2 injection is already underway at locations across the United States and Canada as part of the oil industry.
Pumping CO2 into depleted fields to maintain pressure and help oil flow through rock formations to the base of wells as part of enhanced oil recovery (CO2-EOR) programmes is a well-established process that already accounts for 5 percent of all U.S. oil production, according to the Department of Energy.
In a flagship project spanning the U.S.-Canadian border, nearly 3 million tonnes of CO2 are captured each year from a coal gasification plant in North Dakota and transported by pipeline to Weyburn in Saskatchewan where they are injected to boost oil production.
More than 21 million tonnes of CO2 have been injected since the project at the Weyburn field operated by Cenovus Energy and a neighbouring one at Midale operated by Apache Canada started operating in 2000 and 2005 respectively.
Underground storage is therefore feasible. But the atlas highlights some of the technical challenges that will need to be overcome to turn it from a niche business into one that captures and stores millions or even billions of tonnes every year, on a scale big enough to make a significant difference to regional emissions.
According to the atlas, there are 1,811 large stationary sources emitting over 100,000 tonnes of CO2 per year in the United States, and another 219 in Canada.
Power plants account for by far the largest share of emissions from stationary sources (80 percent in the United States, 45 percent in Canada) but other big emitters include the oil and gas industry, refiners, ethanol distilleries, cement and fertiliser manufacturers, and other heavy industries such as iron and steel.
Chemical plants, ethanol distillers and refiners produce relatively concentrated CO2 which is easier and more economical to capture, transport and inject. In contrast, the stream of CO2 from a conventional coal-fired power plant is much more diluted, making it harder and more expensive to capture, purify and transport.
Policymakers are therefore starting to focus on the potential for capturing CO2 from industries outside the power sector. As part of this effort, the U.S. Energy Department is using stimulus funds to help support three projects expected to capture a total of 6.5 million tonnes of CO2 per year.
In Texas, Air Products and Chemicals Inc is building a project that will capture 1 million tonnes of CO2 per year, starting in November 2012, at its existing steam-methane reformers at Port Arthur, transporting it via pipeline to oil and gas fields in the eastern part of the state to support CO2-EOR programmes.
In Illinois, Archer Daniels Midland is building a project that will capture 1 million tonnes from an existing ethanol distillery, beginning in August 2012, and sequester it in a nearby saline aquifer.
And in the most ambitious project, in Louisiana, Leucadia Energy plans to capture 4.5 million tonnes of CO2 per year from a new methanol plant, to be delivered via a 12 mile pipeline and injected into the West Hastings oil field from April 2014 as part of an EOR programme.
North of the border, Canada's federal government and provincial governments "have committed more than $3 billion to CCS initiatives through a number of federal and provincial programmes," according to the atlas.
Capturing, transporting and injecting CO2 is expensive, so policymakers are talking up the commercial value of CO2 and its usefulness as an input into other industries. The new emphasis is on carbon capture utilisation and storage (CCUS).
The U.S. Energy Department is focusing research and development efforts, and subsidies, on "the economic utilization of captured CO2 for commercial purposes .. By putting the captured CO2 to use, CCUS provides an additional business and market case for companies or organizations to pursue the environmental benefits of CCS" according to an announcement on its website.
The biggest near-term opportunity is an expansion of CO2-EOR programmes. The Energy Department estimates EOR has the potential to add an extra 60 billion barrels to recoverable U.S. oil resources, tripling proven reserves.
In the longer term, researchers are examining CO2 injection to boost the production of coal-bed methane (CBM). CO2 is preferentially adsorbed onto the surface of coal, displacing methane. CO2 injections could therefore boost natural gas production from coal seams in a technology dubbed "enhanced coal bed methane" (ECBM).
The biggest uncertainties, however, surround the size of suitable underground formations for storage. CO2 is toxic in fairly low concentrations (8-15 percent) so no one wants it to escape. Fugitive emissions would also negate the climate change benefits of CCS. Formations therefore need to be picked carefully.
Fortunately, injecting CO2 into depleted oil and gas fields is relatively well understood, though no one has tried to do it on anything like the required scale. Hydrocarbons were safely locked away in these fields for millions of years so the CO2 should be sequestered securely.
But depleted oil and gas fields account for only a small share of the total storage capacity identified in North America. In the United States, for example, depleted fields account for 124 billion tonnes of CO2 storage capacity (7 percent of the total). Unmineable coal seams could sequester another 60-118 billion tonnes (3-7 percent).
The big prize is sequestering CO2 in saline aquifers. The United States could potentially trap 1.6-20.1 trillion tonnes of CO2 in aquifers buried at least 800 metres below ground level, safely below the drinking water table. Saline aquifers account for more than 85 percent of the country's carbon sequestration capacity according to the atlas.
However, there is much more uncertainty about trapping CO2 in brine. Because they have been less important economically, saline formations are not as well mapped. Less is known about how CO2 might flow through them. It would be essential that any aquifer is overlain by a regionally extensive cap rock with no fractures.
Despite the caveats, the atlas does a useful job showing just how much CO2 could be locked up underground, potentially extending North America's oil and gas resources by decades and limiting the impact on the greenhouse effect. But it will only work if technology for separating CO2 from power plant exhausts can be perfected and the right financial incentives are put in place.