TECHNICAL OVERVIEW OF CARBON DIOXIDE SEQUESTRATION TECHNOLOGIES

R. Jason Gwaltney, MPR Associates, Inc.320 King Street, Alexandria Virginia, 22314

703-519-0200/703-519-0224, jgwaltney@mpr.com

INTRODUCTION

PurposeThis paper investigates the leading methods for carbon sequestration and evaluates them on the bases of cost, capacity and environmental consequences. Other factors such as geographical constraints and the current state of technology are also considered. This white paper covers the following post-capture aspects of carbon sequestration:

− Compression− Transport− Storage− Monitoring, Mitigation and Verification (MM&V)

A complementary paper has been written that addresses Carbon Capture: Technical Overview of Carbon Dioxide Capture Technologies for Coal-Fired Power Plants [Reference 4].

BackgroundAtmospheric levels of carbon dioxide (CO

2) have increased from a pre-industrial level of 280 parts-per-million

(ppm) [Reference 15] to today’s level of 379 ppm [Reference 2]. The primary source of anthropogenic CO2 is

combustion of fossil fuels. Studies have shown that capture of anthropogenic CO2 and carbon sequestration

could help to stabilize the concentration of atmospheric CO2 [Reference 1].

There are several approaches to sequestering carbon. Some of them are naturally occurring and are already sequester large amounts of carbon (denoted by asterisks):

− Deep Saline Aquifers− Oil and Gas Reservoirs− Unminable Coal Seams− Direct Injection into Oceans− Terrestrial Sequestration*− Natural Enhancement of Oceans*

It is estimated that terrestrial ecosystems sequester approximately 7 GtCO2/year1 and that the oceans sequester

an additional 7 GtCO2/year [Reference 15]. Over the next 1000 years, the ocean is expected to absorb

approximately 85% of today’s anthropogenic carbon [Reference 15]. Although the level of natural sequestration

1 Billion tons CO2 = 109 tons CO2 = Gigaton CO2 = GtCO2

is impressive, it is no match for the global production of CO2. The 2003 global emissions of CO

2 were

approximately 24 GtCO2 of which 6.4 GtCO

2 was emitted by the U.S. [References 2 and 14].

Several of these carbon sequestration methods are currently in use today. However, none of these methods are sequestering a significant amount of carbon compared to the rate of carbon production. The rates of current levels of sequestration are provided only as a means for comparing the “state of technology”. All of the current sequestration methods should be considered pilot scale.

Cost and Capacity EstimatesThis paper provides costs and capacity estimates for each method of carbon sequestration addressed. Capacity numbers are in terms of billion tons of CO

2 (GtCO

2)2. Some sources describe storage capacity in units of

carbon rather than carbon dioxide3 or metric tons instead of U.S. tons4. Therefore caution must be taken when comparing numbers between sources. Cost estimates are based on the cost for capture, compression, transportation and storage of CO

2. Storage costs are in terms of $ per ton of CO

2 avoided. The “CO

2 avoided”

rather than just “CO2” takes into account that the energy required for capture, compression, transportation and

storage actually increases the emissions of CO2. Additional details on these cost estimates are in the section

entitled Capture and Transport of Carbon Dioxide.

SEQUESTRATION IN DEEP SALINE AQUIFERS

DescriptionDeep saline aquifers are porous rock formations filled with saline or brackish water. Sites suitable for injection are typically located at depths greater than 2,000 ft below the Earth’s surface. Locations for sequestration must be separated from potable water by impermeable rock and they must be deep enough such that the injected CO

2

will remain supercritical. CO2 is stored using three distinct mechanisms: hydrodynamic trapping, solubility

trapping and mineral trapping [Reference 6]. Each of these trapping mechanisms is described in Table 1 below. It is expected that initial containment of CO

2 will be due to hydrodynamic trapping; however, over time,

solubility trapping and then mineral trapping are expected to dominate the CO2 containment.

2 Billion tons CO2 = 109 tons CO2 = Gigaton CO2 = GtCO2 3 One ton of CO2 equals approximately 3.67 tons of carbon 4 One metric ton equals approximately 1.1 U.S. ton

Table 1. CO2 Trapping Mechanisms in Deep Saline Aquifers

Experience to DateStatoil Company is currently sequestering CO

2 into a saline formation 1,000 m under the Norwegian North

Sea [Reference 15]. The Utsira formation is porous sandstone with a shale cap rock, capable of storing up to 600 GtCO

2 [Reference 5]. Through March of 2005, over 6 million tons of CO

25 have been injected. Time-lapse

seismic technology is used to monitor the formation and detect CO2 leakage. No leakage has been detected

through March of 2005.

The Department of Energy is funding a project in Frio, Texas to inject CO2 into a saline aquifer. In 2004,

approximately 1,900 tons of CO2

6 were injected approximately 1,500 meters underground [Reference 1]. The goal of the project is to demonstrate the technology and prove that the underground storage of CO

2 is safe for

both people and the environment.

Looking AheadDeep saline aquifers are located throughout the continental United States as shown in Figure 1. The storage capacity is estimated to be up to 500 GtCO

27; orders of magnitude greater than other forms of geologic storage

[Reference 9]. More research is needed to understand the hydrodynamic, solubility and mineral trapping. Additional research is needed regarding the caprock strength, to evaluate it before injecting CO

2 and to maintain

its strength during injection. There is also a question of whether there is induced seismicity associated with CO2

injection.Courtesy of Oak Ridge Natl. Lab./ US Dept. Of Energy

Courtesy ORNL/DOE and USGS

5 6 million tons CO2 = 0.006 GtCO26 1,900 tons of CO2 = 0.0000019 GtCO27 500 GtCO2 is equivalent to approximately 80 years of the current U.S. anthropogenic carbon emissions

Figure 1. Saline Aquifers in the United States [Reference 15]

There is a need for more studies on specific locations that are candidates for injection. Some aquifers are too deep, while others are too shallow. Models need to be developed to understand how the CO

2 will behave in the

candidate sites.

The cost of deep saline injection is higher than other forms of sequestration. It does not contain any of the added economic benefits associated with other methods of sequestration (e.g. Oil and Gas Reservoirs). The approximate cost for the capture, transportation and storage of CO

2 into saline aquifers is $21 per ton CO

2

avoided [Reference 8].

SEQUESTRATION IN OIL AND GAS RESERVOIRS

DescriptionThere are two basic methods for sequestering CO

2 in oil and gas reservoirs: injection into depleted reserves

and enhanced oil recovery. Injection into depleted reserves is just that; the injection of CO2 into oil and gas

reservoirs that have been exhausted. This method of sequestration is very similar to deep saline aquifers with regard to risk and cost. The second method for sequestration in oil and gas reservoirs is enhanced oil recovery (EOR). Standard extraction methods for oil and gas reservoirs only recover the first 20-40% of the oil and gas [Reference 11]. Any additional extraction of oil requires the use of EOR. There are several methods to perform EOR, only one of which uses CO

2:

− Chemical Flooding− CO

2 Injection

− Hydrocarbon Injection− Thermal Recovery

CO2 injection is a recovery method in which CO

2 is injected into the reservoir at a supercritical state. There are

actually two different mechanisms by which CO2 injection aids in the extraction of oil: miscible and immiscible

extraction. Miscible extraction is when the CO2 mixes thoroughly with the oil and lowers its viscosity.

Immiscible extraction is when the oil and CO2 remain separate; however the CO

2 causes the oil to swell and

improves mobility. All large scale EOR projects in the U.S. use miscible extraction [Reference 11].

Experience to DateBy far, industry has the most experience with carbon sequestration through the use of EOR. This method accounts for over 80% of the commercial CO

2 use in the U.S. [Reference 15]. In 1998, there were 74 active

EOR sites in the U.S. using CO2 to aid in extraction. These sites accounted for approximately 3% of U.S.

production of oil. This effectively sequesters 3.3 million tons of CO28 per year [Reference 11]. However, most

of these facilities are using naturally occurring carbon dioxide from underground deposits, and therefore are not helping to reduce anthropogenic carbon emissions. Even if anthropogenic carbon emissions were used for EOR instead of naturally occurring CO

2, the impact on overall carbon sequestration would be minimal.

There is a project in the Weyburn oil field in Saskatchewan, Canada to sequester anthropogenic carbon via EOR. The Dakota Gasification Co. which operates the Great Plains Synfuels Plant in Beulah, North Dakota constructed a 325 km pipeline between Beulah and Weyburn. CO

2 is transported to Weyburn where it is used

to increase oil recovery. Over the life of the project an estimated 20 million tons of CO2

9 will be sequestered [Reference 5].

Looking AheadIn comparison to other methods, the technology for EOR and injection into depleted reservoirs is very advanced. The long-term storage integrity of the reservoir is high as long as it is not over-pressurized. This method of sequestration also has economic benefits; the estimated cost is $4 per ton of CO

2 avoided when used

for EOR [Reference 8]. When injected into depleted oil and gas reservoirs, the cost is approximately $22-23 per ton of CO

2 avoided, which is nearly the same as injection into saline aquifers [Reference 8]. Figure 2 shows

the locations of gas-producing areas in the U.S.

8 3.3 million tons of CO2 per year = 0.0033 GtCO2 per year9 20 million tons of CO2 = 0.02 GtCO2

Courtesy ORNL/DOE and USGS

Figure 2. Gas-Producing Areas in the United States [Reference 15]

Although EOR using CO2 is presently occurring in the U.S., it is not sequestering anthropogenic CO

2. Oil

companies use the cheapest source of CO2 available: naturally occurring CO

2 from underground deposits.

Without an economic benefit to carbon sequestration, EOR using anthropogenic carbon is unlikely to occur in the short-term. The amount of CO

2 capable of being sequestered through EOR is a small fraction of the total

estimated CO2 sequestration capacity of 40-50 GtCO

2 in oil reservoirs and 80-100 GtCO

2 in gas reservoirs

[Reference 9].

SEQUESTRATION IN UNMINEABLE COAL SEAMS

DescriptionCoal beds contain methane that has been adsorbed onto the pore surfaces of the coal. Unmineable coal seams contain coal bed methane, but are either too deep or too narrow to be mined for the coal. By drilling down and tapping into the beds, this coal bed methane can be extracted and used as a fuel. The extraction process can be augmented through the use of CO

2. The coal preferentially desorbs the methane and adsorbs the CO

2. In this

manner, the CO2 is sequestering CO

2 and facilitating the extraction of methane. For every molecule of methane

desorbed by the coal, 2-3 molecules of CO2 will be adsorbed [Reference 2]. Producing methane will result in

the burning of methane and an increase in CO2 emissions; however, for simplicity it is assumed that methane

production via coal bed methane will offset other existing forms of production. Furthermore, it is important that the released methane be trapped as effectively as possible. Methane is over 20 times more effective than CO

2 as

a greenhouse gas.

It should be noted that CO2 is not the only gas that can be used to extract the coal bed methane. In fact, nitrogen

is more effective at releasing the coal bed methane than CO2. There has been consideration for using a direct

flue gas mixture; however, this substantially reduces the sequestration capacity. Figure 3 shows a notional graph of the effect of CO

2:N

2 ratio on the methane removal effectiveness and carbon sequestration effectiveness.

Mixtures of 100 % CO2 provide moderate levels of gas extraction while maximizing the sequestration potential.

Figure 3. Notional Effects of CO2:N

2 Ratio on Methane Removal and

Carbon Sequestration Effectiveness [Based on Data from Reference 1]

Experience to DateThere are three test platforms in North America for the sequestration of CO

2 into unmineable coal beds: the

San Juan Basin in New Mexico, Alberta Canada and the Central Appalachian Basin in Virginia. The current plan for the San Juan Basin is to inject 280,000 tons of CO

2 over a six-year period [Reference 2]. The Alberta

study began in July 1999 and is headed by the Alberta Research Council, Inc. (ARC). There are several phases to the project, including preliminary modeling to determine feasibility, small-scale pilot testing and full-scale pilot testing. The ARC is also evaluating the steps required to prepare the gas for injection, including flue gas treatment and compression. Consol Energy plans to inject 26,000 tons of CO

210 over 1 year into an unmineable

coal seam in the Central Appalachian Basin starting in 2005 [Reference 2].

There are countless other studies that attempt to model gas recovery from coal bed methane. For example, the Dutch performed a program called the Feasibility of Carbon Dioxide Disposal and Coal Bed Methane Production in the Netherlands [Reference 10]. The study indicates that theoretically, there is sufficient coal

10 26,000 tons of CO2 = 0.000026 GtCO2

bed methane in the Netherlands to meet the national energy demand for 20 years. Furthermore, the theorized storage capacity for CO

2 in unmineable coal beds is sufficient to store all of the Netherlands’ CO

2 emissions for

the next 40 years.

Looking AheadThe storage capacity for unmineable coal seams is estimated at 100 GtCO

211; however, nearly 50% of this

capacity is located in Alaska [Reference 2]. One major hurdle to enhanced coal bed methane recovery is the phenomena of coal swelling. When CO

2 is injected into the coal it has a tendency to swell and reduce

permeability. This reduces both the flow of CO2 into the coal seam and the outlet flow of methane. Nitrogen

does not cause coal swelling, and given its superior ability to remove methane, its use is preferred over CO2.

There will probably need to be economic benefit to sequestering CO2 for CO

2 injection to be selected over

nitrogen.

The cost of CO2 sequestration via unmineable coal seams is strongly dependent upon natural gas prices.

Sequestration costs decrease by approximately $1/ton for each $1/MMBTU increase in the natural gas price [Reference 1]. At today’s price for natural gas (approximately $7/MMBTU), the cost of sequestration is approximately $6-8 per ton CO

2 avoided [References 1 and 8].

OCEAN SEQUESTRATION VIA DIRECT INJECTION

DescriptionAt first glance, this process is as simple as the name implies: liquified CO

2 is injected deep into the ocean.

At depths greater than 1000 m, the CO2 will be at approximately the same density as water and will remain

suspended. Upon further inspection, there are actually several different approaches to injecting CO2 as shown

in Table 2:

11 100 GtCO2 is equivalent to approximately 15 years of the current U.S. anthropogenic carbon emissions

Table 2. Injection Methods for Ocean Sequestration [References 12 and 13]

The uncertainty surrounding CO2 injection is focused on three distinct questions:

1. How does the CO2 behave once injected?

2. How does the CO2 affect oceanic organisms?

3. How much of the CO2 remains sequestered over time?

Injected CO2 may be immediately dissolved into the water. Once dissolved, the injected CO

2 will be subjected

to underwater currents. Changes in temperature (and therefore density) will allow the water to rise or fall. Fluid models of underwater currents have made attempts to estimate the spread of the CO

2 once injected;

however, modeling underwater currents and diffusion of CO2 is very difficult. If ultra-cold CO

2 is injected,

it will form a solid lake with an ice-like layer of CO2 hydrate as its exterior. CO

2 hydrates are compounds

formed by CO2 and minerals in the water at low temperature and high pressure, which makes studying hydrate

formation very complex. Formation of carbon hydrates may add to the stability of injected CO2. Blocks of dry

ice could also be dropped into the ocean, but this is not practical due the large amount of energy required to convert the CO

2 from liquid to solid state.

The interaction of CO2 with oceanic organisms is of paramount interest to researchers. Higher concentrations

of CO2 in water can already be observed; however the effects of pH changes may be the most significant. The

pH level of the ocean is already 0.1 pH units lower than in the 19th century [Reference 12]. It is estimated that changes of pH in excess of 0.2 pH units may have a detectable biological impact [Reference 13].

The sequestration of CO2 in the oceans is a temporary, albeit long-term, form of storage. Over a period of

centuries, the CO2 will gradually leak out into the atmosphere at rates between 0-0.5% per year [Reference 13].

Modeling suggests that >75% of carbon injected at 3000 m is sequestered for more than 500 years [Reference 13]. Regardless, the oceans have the potential to sequester enormous amounts of carbon and there are still substantial benefits for the temporary storage of CO

2.

Experience to DateTo date, there has been strong public resistance to large-scale injection of liquified CO

2 into the ocean. In the

late 90’s the National Energy Laboratory of Hawaii Authority (NELHA) attempted to inject CO2 into the ocean

off the coast of the Big Island. From a scientific perspective, the location was suitable for the experiment. However, local opposition derailed the project and to date, no large scale testing has been performed. The technology to inject the CO

2 is not complex; however, it is unclear how the CO

2 will behave once injected.

Looking AheadBy far, ocean sequestration has the largest environmental and sociological roadblocks of any method. Temporary storage of CO

2 means that over a period of centuries, the CO

2 will eventually be released back into

the atmosphere. Additionally, this sequestration method must be paired with stationary CO2 sources near the

ocean. These sources only account for 15 to 20% of the anthropogenic CO2 emissions in the U.S. [Reference

15].

The cost of carbon sequestration via a pipeline is $24 per ton CO2 avoided and for a tanker is $39 per ton CO

2

avoided [Reference 8]. The depth of the injection also has an effect on price; the deeper the injection, the higher the cost. The cost penalty for deep injections may be offset by the reduction in leakage back to the atmosphere in comparison to shallow injection. This will require that there be some economic value to the temporary sequestration of CO

2.

TERRESTRIAL SEQUESTRATION

DescriptionTerrestrial sequestration is part of the natural CO

2 cycle on Earth whereby trees and plants absorb CO

2 via

photosynthesis. It is estimated that the net absorption of CO2 by the terrestrial biosphere is approximately

7 GtCO2 per year [Reference 15]. Storage of CO

2 in soils, plants and trees is actually a temporary form of

storage. Events such as fire, insect infestations and changes in land-use allow the release of the stored carbon dioxide. Basically, whenever the plants die and decompose, they release their carbon. The exception to this is the creation of wood products that have a long-term use (e.g. construction materials).

Terrestrial sequestration is the development and maintenance of ecosystems such that carbon storage is maximized. Preventing emissions of carbon is just as important as storing additional carbon; therefore some terrestrial sequestration efforts focus on maintaining levels of sequestration in certain ecosystems rather than developing additional growth. Methods for increasing terrestrial sequestration include:

− Increasing photosynthetic carbon fixation− Reducing decomposition of organic matter− Reversing land-use changes that contribute to global emissions− Creating energy offsets through biofuels or other products (e.g. wood products)

In addition to trees and plants, soils contain a great deal of carbon. Approximately 75% of the terrestrial carbon is currently contained in soils [Reference 15]. It is important to understand what mechanisms increase the

carbon uptake of the soils and how carbon storage can be maximized. Soil erosion releases the carbon stored within soils. Agricultural practices such as tilling greatly reduce the amount of carbon stored in the soil.

Experience to DateFor decades, the U.S. has been managing its forests with a focus on sustaining timber yields. Recently, more attention has been given to forest management with regard to forest fires.Countless projects have been demonstrated which improve carbon storage, including: no-till farming, erosion prevention, planting forests, slowing deforestation and wetland preservation.

Looking AheadIt is estimated that the net storage of CO

2 by terrestrial ecosystems is 7 Gt/CO

2 per year (globally), but could

be over 20 Gt/CO212 per year [Reference 15]. There is some upper limit on carbon storage in the terrestrial

ecosystem, but it is unclear what that limit is. Further research is needed to:

− Develop methods for measuring carbon uptake in a given ecosystem− Estimate the potential for total carbon storage in a given ecosystem− Estimate the length of time over which the increased uptake could be sustained− Develop methods for monitoring the uptake in an ecosystem

OCEAN SEQUESTRATION VIA NATURAL ENHANCEMENT

DescriptionCO

2 concentrations in the atmosphere and the ocean attempt to maintain equilibrium. Currently, there is an

excess of CO2 in the atmosphere and the ocean is absorbing CO

2 faster than it is releasing it to the atmosphere.

Once dissolved into the ocean, a portion of the CO2 is consumed by ocean organisms, such as phytoplankton.

Eventually the phytoplankton are either eaten by larger organisms, or die and sink to deeper waters. Through this process of CO

2 absorption, consumption and sinking, the ocean acts as a biological pump for CO

2. It is

estimated that this natural pathway will eventually remove 85% of today’s anthropogenic carbon [Reference 15]. Ocean sequestration via natural enhancement increases the rate at which this natural pump operates. This is accomplished through the injection of micronutrients into the ocean. For example, phytoplankton require ammonia, phosphorous and iron to grow. Some areas of the ocean contain sufficient levels of ammonia and phosphorous, but are lacking in iron. When iron is added to these areas, the phytoplankton flourish and there is a temporary, but substantial uptake in CO

2. There is a distinct advantage to adding iron over the other nutrients

(e. g. phosphorous). Provided below are the ratios of nutrients consumed by the phytoplankton, which include carbon (C), nitrogen (N), and phosphorous (P) [Reference 7]. The ratio of carbon to iron consumption is quite large, such that one ton of iron will sequester at least 23,000 tons of carbon (or 84,000 tons of CO

2).

106 C : 16 N : 1 P : (0.001 - 0.005) Fe

12 Global emissions of CO2 are approximately 24 GtCO2 per year [Reference 2]

Experience to DateA series of iron fertilization experiments have been performed over the last few years [Reference 3]:

Table 3. Ocean Fertilization Experiments

In these experiments iron was added to areas deficient in iron, but containing excess nitrogen and phosphorous. Within hours of the addition of iron, the phytoplankton growth increased dramatically and the partial pressure of CO

2 above the water surface decreased [Reference 15]. Several patents have already been registered for ocean

fertilization, including details such as a spiral pattern of fertilization.

Looking AheadThis method of carbon sequestration has environmental concerns similar to those for direct injection. Questions regarding the effects of increased carbon uptake on the overall ecosystem are still unanswered. Natural enhancement should be thought of as a temporary method for CO

2 storage. Eventually the captured carbon will

be released into the atmosphere.

Given that this is an indirect method of sequestration, there are no geographical limitations with regard to anthropogenic sources of CO

2. However, to be considered a candidate for natural enhancement, the site will

have to contain high levels of nutrients, but low chlorophyll. There are three areas that have been identified as candidate sites for natural enhancement [Reference 7]:

4. Eastern Equatorial Pacific

5. NE Subarctic Pacific

6. Southern Ocean

The Southern Ocean represents the largest potential source for carbon sequestration. It is estimated that it could sequester 180 to 550 GtCO

213 over 100 years of fertilization [Reference 7]. However, through global ocean

currents, waters in Southern Ocean reemerge in the tropics. Therefore increased growth of phytoplankton in the Southern Ocean may reduce growth in the tropics by 30 to 70% [Reference 7]. There are other drawbacks to ocean fertilization. Dimethyl sulfide production by phytoplankton increases during fertilization, and N

20 may

be produced as a result of high nitrogen content in low oxygen areas. N20 is approximately 250 times more

powerful as a greenhouse gas than CO2. There are many issues that need to be resolved before large-scale ocean

fertilization is utilized.

13 At the current carbon emission rates, the world will produce 2,400 GtCO2 over the next 100 years [Reference 2]

CAPTURE, COMPRESSION AND TRANSPORT OF CARBON DIOXIDE

As discussed in the introduction, the scope of this white paper is limited to the sequestration, compression, transport and storage of CO

2. A complementary paper has been written that addresses Carbon Capture:

Technical Overview of Carbon Dioxide Capture Technologies for Coal-Fired Power Plants [Reference 4]. Note that all of the direct methods for sequestering carbon require the transport of CO

2 from the power plant to the

sequestration site (e.g. wellhead). CO2 is most economically shipped when liquified. In general, it is expected

that the CO2 will be pressurized to approximately 2000 psi and have a 500 psi pressure drop due to piping losses

[Reference 1 and 8]. All of the sequestration costs provided in the previous sections have accounted for the costs of capture, compression, transportation and storage. It is important to consider all of these costs when comparing two diverse methods such as Ocean Sequestration through Direct Injection and Ocean Sequestration through Natural Enhancement. Both methods sequester carbon in the ocean, but direct injection requires the capture, compression and transport of liquified CO

2. The following assumptions were used to calculate the

capture, compression and transportation costs:

Table 4. Parameters for Carbon Sequestration Cost-Estimates [Reference 8]

POST-INJECTION MONITORING, MITIGATION AND VERIFICATION

Without exception, each method of carbon sequestration requires careful monitoring, both to ensure safety and to verify the storage effectiveness. The developing industry of carbon sequestration has coined the term MM&V to describe this step in carbon sequestration. MM&V is the Post-Injection Monitoring, Mitigation and Verification of sequestered carbon. The objectives of MM&V are to measure the amount of sequestered carbon, monitor the area for leaks or problems that may lead to leaks, mitigate leaks or damage to the host environment and verify that the sequestered carbon is interacting with its host environment in a manner that was expected. The following list highlights several methods that can be used to monitor sequestered carbon:

− Subsurface - Monitors the sequestered CO2 to detect leakage

− Ultrasonic testing− Observation wells− 3D seismic− Cross-well seismic

− Soils - Monitors the carbon uptake of the soil above the sequestration area− Soil monitors− Leakage pathways into the atmosphere

− Above-ground - Monitors the carbon uptake of vegetation− Vegetation monitoring

Modeling of sequestered carbon is a key element to MM&V. When measuring the actual conditions of stored carbon, it is important to be able to compare the findings to predicted values.

There are two existing projects that highlight unique methods for monitoring carbon sequestration: Ultrasonic testing and M3DADI. Ultrasonic testing has been used in the Sleipner field in the Norwegian North Sea. Results to date indicate that no leakage has occurred. It is estimated that using 3D seismic methods, CO

2

deposits as small as 2,750 tons can be detected [Reference 5]. M3DADI is a Multi-Spectral 3-Dimensional Aerial Digital Imagery camera being developed by the DOE. It uses two cameras and a laser attached to a plane to map out forest vegetation and estimate carbon storage [Reference 2]. The technology is currently being validated against conventional methods for measuring carbon storage in forests.

Accurate verification of carbon storage will also be an essential aspect to the economy of carbon storage. Both enhanced oil recovery and coal bed methane recovery have the potential to sequester carbon, but are lacking the economic motivation. Without a value associated with the sequestration of carbon, easy opportunities for sequestration will be missed. It is also important to assign an economic value to the temporary storage of carbon. Some methods are guaranteed to leak some percentage of the sequestered carbon over the next few centuries. Accurate verification through MM&V will enable trading of carbon storage credits.

CONCLUSIONS

The long-term feasibility of any carbon sequestration method will be governed by its cost, capacity, technical feasibility, and environmental consequences. Each of the sequestration methods in this paper has its own unique opportunities and challenges. Table 5 provides a comparison of the six different sequestration methods discussed in this paper.

Terrestrial sequestration and oil and gas reservoir sequestration are the most likely to be the forerunners because industry has the most experience with these methods. On the other hand, ocean sequestration, both by direct injection and natural enhancement, presents some of the largest risks. There is a higher rate of CO

2 leakage

back into the atmosphere and greater uncertainty with regard to environmental impact. Carbon sequestration in oceans is a technology that will have to be proven more thoroughly before implementation.

Carbon sequestration is in its infancy. The test programs underway have the capacity to sequester less than 0.1% of the annual global production of CO

2. The infrastructure required to sequester approximately 10% of

the annual U. S. production of CO2 is estimated to be of the same order as the existing natural gas production

and distribution infrastructure. A strong commitment from the public and significant economic incentives, that are currently absent, will be required to make carbon sequestration a reality.

Acceptance of carbon sequestration will require the development of reliable Monitoring, Mitigation and Verification (MM&V) of sequestered carbon. Reliable MM&V goes hand-in-hand with public acceptance and placing an economic value on carbon sequestration. There must be reliable data that ensure the CO

2 is being

effectively sequestered.

Table 5. Comparison of Sequestration Options

1 There is approximately 55 GtCO2 of capacity in the continental U.S. with an additional 45 GtCO

2 of capacity

in Alaska.

REFERENCES

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2002.

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January 8, 2002.

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Netherlands. Utrecht, March 2001.

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(Footnotes)1 Billion tons CO

2 = 109 tons CO

2 = Gigaton CO

2 = GtCO

22 Billion tons CO

2 = 109 tons CO

2 = Gigaton CO

2 = GtCO

23 One ton of CO

2 equals approximately 3.67 tons of carbon

4 One metric ton equals approximately 1.1 U.S. ton5 6 million tons CO

2 = 0.006 GtCO

26 1,900 tons of CO2 = 0.0000019 GtCO

27 500 GtCO

2 is equivalent to approximately 80 years of the current U.S. anthropogenic carbon emissions

8 3.3 million tons of CO2 per year = 0.0033 GtCO

2 per year

9 20 million tons of CO2 = 0.02 GtCO

210 26,000 tons of CO

2 = 0.000026 GtCO

211 100 GtCO

2 is equivalent to approximately 15 years of the current U.S. anthropogenic carbon emissions

12 Global emissions of CO2 are approximately 24 GtCO2 per year [Reference 2]

13 At the current carbon emission rates, the world will produce 2,400 GtCO2 over the next 100 years [Reference 2]