Carbon Sequestration

With financially compelled environmental reform underway, companies are looking for ways to reduce their green house gas (GHG) emissions. Underground carbon sequestration is one of those ways. This post will outline the basic concept, sans lots of technical science, of how carbon is sequestered.

Currently, carbon can be sequestered either geologically or terrestrially.

Terrestrial sequestration is how carbon is stored naturally, through photosenthysis. According to coloradotrees.org, “A single mature tree can absorb carbon dioxide at a rate of 48 lbs./year and release enough oxygen back into the atmosphere to support 2 human beings.” Mother nature provides this, most likely to offset the CO2 emitted through respiration – which is explored in another one of my posts Tax on Breathing. Additionally, the DOE estimates that “The global biosphere absorbs roughly 2 billion tons of carbon annually, an amount equal to roughly one third of all global carbon emissions from human activity. Significant amounts of this carbon remains stored in the roots of certain plants and in the soil. In fact, the inventory of carbon stored in the global ecosystem equals rougly 1,000 years worth of annual absorption, or 2 trillion tons of carbon.”

2 billion tons of carbon seems like a good start, however, human activity emits an estimated 28,432 million metric tons of CO2 – way more than mother nature can keep up with. So, we explore for alternative means of storage.

Geologic carbon sequestration is the process of capturing CO2, pressurizing it, and injecting it back into the earth. Diminished oil fields are the ideal candidates for geologic carbon sequestering, as the CO2 loosens residual oil from porous rock formations and pushes it back upwards. This is commonly done through a process called enhanced oil recovery. The effects of carbon sequestered in this way are well understood and considered safe, so long as the original pressure of the well is not exceeded. When all the oil that can be reasonably recovered has been, the wells are plugged with cement and the CO2 remains underground. Sequestering carbon in depleted oil fields kills two bird with one stone, increased domestic oil production and reduced GHG emissions. Unmineable coal seams and underground saline formations are also potential options for storing CO2 underground.

According to the DOE, “the United States is the world leader in enhanced oil recovery technology, using about 32 million tons of CO2 per year for this purpose. From the perspective of the sequestration program, enhanced oil recovery represents an opportunity to sequester carbon at low net cost, due to the revenues from recovered oil/gas.” In comparison, it would take 1,904,761.9 million acres of trees (700 trees/acre & 48lbs of CO2/tree/year), which is a little more than 2.5 Rhode Islands, to sequester the same amount of CO2 that the United States currently sequesters via enhanced oil recovery.

DOE Diagram of Carbon Sequestration Methods

Coal beds are another geologic option for carbon sequestration. Here, CO2 is injected into coal beds in an effort to displace methane trapped in the formation. According to the DOE, “tests have shown the absoprtion rate for CO2 to be approximately twice that of methane, giving it the potential to effectively displace methane and remain sequestered in the bed. CO2 recovery of coal bed methane has been demonstrated in limited field tests, but much more work is necessary to understand and optimize the process.”

By utilizing CO2 to enhance recovery of methane, sequestering carbon in methane-rich coal beds shares many of the same benefits that enhanced oil recovery sequestration does. Both applications create a low net cost option to reduce GHG emissions into the atmosphere. CO2 can also be injected into unmineable coal seams, close to coal fired power plants, which reduces the transportation costs in disposing of the CO2. Integrating enhanced coal bed methane recovery with a coal-fired electricity generating system allows for additional, low-emissions power generation, as the CO2 emitted can be both stored and used to recover additional fuel.

Saline formations are yet another viable geologic formation, in which, carbon can be stored. While there are no value-added by-products involved with storing carbon in saline formations, there are other advantages. Saline formations provide an almost unlimited storage capacity, estimated at 500 billion tonnes of CO2. Saline formations are also much more common than coal beds, or oil wells, which reduces transport costs and makes it easier to inject CO2 underground, closer to its source. Click here to see a map of saline formations suitable for CO2 storage. However, more research is needed to determine whether or not saline formations will in fact permanently trap the CO2. Ensuring the sequestered CO2 does not leak into water tables is critical.

According to the DOE, US based oil companies routinely inject brines into saline reservoirs – a practice approved by the EPA. Additionally, the EPA has permitted the injection of certain hazardous wastes into saline formations. In Norway, Statoil, a Norwegian oil company, currently injects upwards of 1 million tonnes of CO2 per year into the Utsira Sand, an under sea saline formation. 1 million tonnes of CO2 is equivalent to the emissions from a 150-megawatt coal-fired power plant.

Related posts:

1. Tax on Breathing Assuming global CO2 emissions of 28,432 million metric tons, humans...
2. Oil Companies Sued for Katrina Over the last decade, global warming has become a hot...

Tags: Energy, Finance, Global Warming

This entry was posted on Monday, November 30th, 2009 at 6:12 pm and is filed under Energy, Legal Issues. You can follow any responses to this entry through the RSS 2.0 feed.