C02 Sequestration

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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, [email protected]

INTRODUCTION

Purpose

This 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].

Background

Atmospheric levels of carbon dioxide (CO2) have increased from a pre-industrial level of 280 parts-per-million

(ppm) [Reference 15] to todays level of 379 ppm [Reference 2]. The primary source of anthropogenic CO2 iscombustion of fossil fuels. Studies have shown that capture of anthropogenic CO

2and 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 todays anthropogenic carbon [Reference 15]. Although the level of natural sequestration

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


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

2were

approximately 24 GtCO2

of which 6.4 GtCO2

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 currentsequestration methods should be considered pilot scale.

Cost and Capacity Estimates

This paper provides costs and capacity estimates for each method of carbon sequestration addressed. Capacity

numbers are in terms of billion tons of CO2

(GtCO2)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 CO2. Storage costs are in terms of $ per ton of CO

2avoided. The CO

2avoided

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

Description

Deep 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 Earths surface. Locations for sequestration must

be separated from potable water by impermeable rock and they must be deep enough such that the injected CO2

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 CO2

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 = GtCO23 One ton of CO2 equals approximately 3.67 tons of carbon4 One metric ton equals approximately 1.1 U.S. ton


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Table 1. CO2

Trapping Mechanisms in Deep Saline Aquifers

Experience to Date

Statoil Company is currently sequestering CO2

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 GtCO2

[Reference 5]. Through March of 2005, over 6 million tons of CO25 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 CO26 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 CO2

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 GtCO27; 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 CO2

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


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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 CO2

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 CO2 into saline aquifers is $21 per ton CO2avoided [Reference 8].

SEQUESTRATION IN OIL AND GAS RESERVOIRS

Description

There are two basic methods for sequestering CO2

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 CO2:

Chemical Flooding

CO2

Injection

Hydrocarbon Injection

Thermal Recovery


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CO2

injection is a recovery method in which CO2

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 CO2

causes the oil to swell and

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

Experience to Date

By far, industry has the most experience with carbon sequestration through the use of EOR. This method

accounts for over 80% of the commercial CO2

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 CO2, 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 Dakotaconstructed a 325 km pipeline between Beulah and Weyburn. CO

2is transported to Weyburn where it is used

to increase oil recovery. Over the life of the project an estimated 20 million tons of CO29 will be sequestered

[Reference 5].

Looking Ahead

In 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 CO2

avoided when used

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

per ton of CO2

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


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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 CO2. Oil

companies use the cheapest source of CO2

available: naturally occurring CO2

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 CO2capable of being sequestered through EOR is a small fraction of the total

estimated CO2

sequestration capacity of 40-50 GtCO2in oil reservoirs and 80-100 GtCO

2in gas reservoirs

[Reference 9].

SEQUESTRATION IN UNMINEABLE COAL SEAMS

Description

Coal 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 beaugmented through the use of CO2. The coal preferentially desorbs the methane and adsorbs the CO

2. In this

manner, the CO2

is sequestering CO2

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 CO2

as

a greenhouse gas.


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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 CO2:N

2ratio 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

2Ratio on Methane Removal and

Carbon Sequestration Effectiveness [Based on Data from Reference 1]

Experience to Date

There are three test platforms in North America for the sequestration of CO2

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 CO2

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 CO210 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 theFeasibility 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


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

storage capacity for CO2

in unmineable coal beds is sufficient to store all of the Netherlands CO2

emissions for

the next 40 years.

Looking Ahead

The storage capacity for unmineable coal seams is estimated at 100 GtCO211

; however, nearly 50% of thiscapacity is located in Alaska [Reference 2]. One major hurdle to enhanced coal bed methane recovery is

the phenomena of coal swelling. When CO2

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 CO2

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 todays price for natural gas (approximately $7/MMBTU), the cost of sequestration is

approximately $6-8 per ton CO2 avoided [References 1 and 8].

OCEAN SEQUESTRATION VIA DIRECT INJECTION

Description

At first glance, this process is as simple as the name implies: liquified CO2

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


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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 CO2

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 CO2 once injected;however, modeling underwater currents and diffusion of CO

2is very difficult. If ultra-cold CO

2is injected,

it will form a solid lake with an ice-like layer of CO2

hydrate as its exterior. CO2

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 CO2

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 19

th

century [Reference 12]. It is estimated thatchanges 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 CO2.


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Experience to Date

To date, there has been strong public resistance to large-scale injection of liquified CO2

into the ocean. In the

late 90s 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 CO2 is not complex; however, it is unclear how the CO2 will behave once injected.

Looking Ahead

By far, ocean sequestration has the largest environmental and sociological roadblocks of any method.

Temporary storage of CO2

means that over a period of centuries, the CO2

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 CO2

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 atmospherein comparison to shallow injection. This will require that there be some economic value to the temporary

sequestration of CO2.

TERRESTRIAL SEQUESTRATION

Description

Terrestrial sequestration is part of the natural CO2

cycle on Earth whereby trees and plants absorb CO2

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 CO2

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


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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 Date

For 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 Ahead

It is estimated that the net storage of CO2

by terrestrial ecosystems is 7 Gt/CO2

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

Description

CO2

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 CO2

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 CO2

absorption, consumption and sinking, the ocean acts as a biological pump for CO2. It is

estimated that this natural pathway will eventually remove 85% of todays 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 CO2. 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 CO2).

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

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


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Experience to Date

A 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 ofCO

2above 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 Ahead

This 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 CO2

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 CO2. 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 GtCO213 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 N20 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]


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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 CO2. 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 CO2

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 CO2. The following assumptions were used to calculate the

capture, compression and transportation costs:

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


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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, CO2

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 ofcarbon. 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.


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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 CO2

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 CO2. The infrastructure required to sequester approximately 10% of

the annual U. S. production of CO2is 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, thatare 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 CO2

is being

effectively sequestered.


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Table 5. Comparison of Sequestration Options

1 There is approximately 55 GtCO2

of capacity in the continental U.S. with an additional 45 GtCO2

of capacity

in Alaska.


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January 8, 2002.

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Sequestration and Enhanced Coalbed Methane Production in the

Netherlands. Utrecht, March 2001.

12. Electric Power Research Institute. Enhanced Oil Recovery Scoping Study. Final Report #TR-113836, October 1999.

13. Brewer, P.G. Progress in Direct Experiments on the Ocean Disposal of Fossil Fuel CO2. First National Conference on Carbon Sequestration,Washington, D.C. May 14-17, 2001.

14. Caldeira, K., Herzog, H.J., and Wickett, M.E. Predicting and Evaluating the Effectiveness of Ocean Carbon Sequestration by Direct Injection.

First National Conference on Carbon Sequestration, Washington, D.C. May 14-17, 2001.

15. Annual Energy Review 2003, Table 12: Environmental Indicators. Energy Information Administration, 2003.

16. Department of Energy. Carbon Sequestration Research and Development. Office of Science and Office of Fossil Energy, December 1999.

(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

2equals 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

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

8 3.3 million tons of CO2

per year = 0.0033 GtCO2

per year9 20 million tons of CO

2= 0.02 GtCO

210 26,000 tons of CO

2= 0.000026 GtCO

211 100 GtCO

2is 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 GtCO

2over the next 100 years [Reference 2]

C02 Sequestration

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