Geologic Sequestration: the Big Picture 

Estimation of Storage Capacity or How Big is Big Enough

Susan Hovorka, Srivatsan Lakshminarasimhan, JP NicotGulf Coast Carbon Center

Bureau of Economic GeologyJackson School of GeosciencesThe University of Texas at Austin

Presented to TXU Carbon Management ProgramIAP for CO2 Capture by Aqueous Absorption Semi-annual meeting,

Pittsburg, May 7, 2007

Large Volumes in the Subsurface NETL National Atlas Estimate

Space for 1,014 to 3,370 109 metric tons of CO2

Saline Aquifers Coal

156 - 183109 metric tons of CO2

92 109 metric tons of CO2

Oil and gas reservoirs

http://www.netl.doe.gov/publications/carbon_seq/atlas/index.html

Amount of CO2 to be sequestered

• 7 x 109 T/year US emissions anthropogenic CO2

• If spread evenly over US as CO2:3 cm/year at @STP

0.04 mm/year at reservoir conditions

Sources dot size proportional to emissions

Sinks color proportional to thickness

3.9 shown here

Options for Estimating Capacity

• Volumetric approach: Total pore volume x Efficiency factor (E)– Free CO2 volume in structural and stratigraphic traps– Trapped CO2 residual phase

• Volume dissolved• Volume that can be stored beneath an area

constrained by surface uses or by other unacceptable risks – well fields, faults

• Pressure limits as a limit on capacity• Displaced water as a limit on capacity

Vol

umet

ricR

isk-

base

d

Volumetric Approach

• How much will go in?– Volumetric

approach – current state of art

– A focus on the two phase region: where is the CO2?

Risk or Consequences Approach to Capacity

• How much will go in before unacceptable consequence occurs?

Fluid Displacement as a Limit on Capacity

• Rate of injection limited by displacement of one fluid by another

• Unacceptable displacement of brine

Total Pore Volume

• Total pore volume = volume of fluids presently in the rock = porosity x thickness x area.

• Not all volume is usable:– Residual water– Minimum permeability cut off– Sweep efficiency

• bypassing and buoyancy

Heterogeneity – Dominant Control on Volumetrics

Structural closure

3-D SeismicStratal Slice

Ambrose (2000) 1000 ft

Reservoir heterogeneity – more important in injection than

production

Cornelius ReservoirMarkham No.

Bay City No. field

Tyler andAmbrose (1986)

Stacked Closure

Higher volumessummed though multiple

zones

Efficiency in Terms of Use of Pore Volume – by-passed volume

Tom Daley LBNL

CO2 Saturation Observed with Cross-well Seismic Tomography at Frio

By-passed volume

Hypothesis Capacity is Related To Heterogeneity

Ca

pac

ity

Heterogeneity

Seal

Low heterogeneity – dominated by buoyancy

Seal

High heterogeneity-poor injectivity

Seal

Just right heterogeneityBaffling maximizes capacity

Options for Estimating Capacity

• Volumetric approach: Total pore volume x Efficiency factor (E)– Free CO2 volume in structural and stratigraphic traps– Trapped CO2 residual phase

• Volume dissolved• Volume that can be stored beneath an area

constrained by surface uses or by other unacceptable risks – well fields, faults

• Pressure limits as a limit on capacity• Displaced water as a limit on capacity

Capacity: Dissolution of CO2 into Brine –

Volumetrically a big unknown

1yr

5 yr

30 yr

40 yr

130 yr

330 yr

930 yr

1330 yr

2330 yr

Jonathan Ennis-King, CO2CRCJonathan Ennis-King, CSRIO

Rapid Dissolution of CO2 in Field Test – a significant factor in

reducing plume size Frio CO2 injection (Oct. 4-7/04)

5.5

6.0

6.5

7.0

4-Oct-04 5-Oct-04 6-Oct-04 7-Oct-04 8-Oct-04

Time

pH

1

10

100

1000

10000

Fe

(mg

/L)

pH

Fe

Yousif Kahraka USGS

Within 2 days, CO2 has dissolved into brine and pH falls, dissolving Fe and Mn

Options for Estimating Capacity

• Volumetric approach: Total pore volume x Efficiency factor (E)– Free CO2 volume in structural and stratigraphic traps– Trapped CO2 residual phase

• Volume dissolved• Volume that can be stored beneath an area

constrained by surface uses or by other unacceptable risks – well fields, faults

• Pressure limits as a limit on capacity• Displaced water as a limit on capacity

Capacity in a Geographically limited area

1-45-10

10-30

>30

Wells perSq km

Role of Risk: Traps available you assume faults sealing and/or well completions acceptable

Structural closure

Do Not Need Structure to Limit Plume Size – Role of Kv/Kh

Seal

Kv <<<Kh

Weak layering allowsrapid vertical migration=

Large spread beneath seal

Seal

Kv <Kh

Effective horizontal baffling layers limitvertical rise – avoid spread below

seal

Kh= Horizontal permeability Kh = vertical permeability. Related to rock fabric,Interpreted from sedimentary depositional environment

Options for Estimating Capacity

• Volumetric approach: Total pore volume x Efficiency factor (E)– Free CO2 volume in structural and stratigraphic traps– Trapped CO2 residual phase

• Volume dissolved• Volume that can be stored beneath an area

constrained by surface uses or by other unacceptable risks – well fields, faults

• Pressure limits as a limit on capacity• Displaced water as a limit on capacity

Nearly Closed Volume – Maximum Capacity May be Pressure Determined

Injection Pressure and Depth

• Maximum injection pressure must be less than fracture pressure

• Fracture pressure estimated to linearly increase with depth of formation

• Volume injected below fracture pressure increases with depth

Maximum CO2 injected (Vi) for Given Pore Volume (Vp)

• Closed domain at several porosities and several different sizes leading to a range of brine-filed volumes Homogeneous geological formation, dimensions 10,000 ft x 10,000 ft x 1000 ft, and permeability 10 md, depth 7000 ft. Maximum pressure set at 75% lithostatic.

10% porosity

20% porosity

30% porosity

Effect of Depth of formation

• Effect of the depth of formation almost entirely due to that of injection pressure

Effect of pore volume (contd)

• Best fit over entire data suggest linear (blue) scaling • Ratio of injected to pore volume is about 1.5 %

Vi = 0.01481 Vp

Options for Estimating Capacity

• Volumetric approach: Total pore volume x Efficiency factor (E)– Free CO2 volume in structural and stratigraphic traps– Trapped CO2 residual phase

• Volume dissolved• Volume that can be stored beneath an area

constrained by surface uses or by other unacceptable risks – well fields, faults

• Pressure limits as a limit on capacity• Displaced water as a limit on capacity

Open Hydrologic System

Fluid Displacement From an Open Hydrologic System

0

100

200

300

400

500

600

700

800

0 250 500 750 1000

Time from Start of Injection (years)

To

tal W

ate

r F

lux

(M

m3 /y

r)

0

100

200

300

400

500

Inje

cti

on

Ra

te (

Mt

CO

2/y

r)

Injection rate

Total water flux at 30 km

Total water flux at 100 km

Output of an analytical model. Total means across the boundaries Vb1 and Vb2. Note: vertical axes are approximately equivalent (500 tons of CO2 is 500 t / 0.6 t/ m3 = 833 m3 of displaced water)

Carrizo-Wilcox System in Central Texas

From Dutton et al., 2003

SENW

Lee Co. Fayette Co. Colorado Co.

Youngerformat ions

Older formations

Base of potable water

Topgeopressured

zone

Faults

Faults

Ground surface

Carrizo

0

-2,000

-4,000

-6,000

-8,000

-10,000

-12,000

-14,000 Vertica l scale greatly exaggerated

0

0

40 mi

40 km

Calvert Bluff

Simsboro

Hooper

College StationWell Field

CO2 Injection

Fate of a Pressure Pulse in a Confined Aquifer

0

50

100

150

200

250

300

350

400

450

500

2000 2010 2020 2030 2040 2050

Calendat Year

Pro

du

ced

/In

ject

ed V

olu

me

(mil

lio

n m

3)

All Pumping

Pumping from Simsboro (L5)

CO2 Injection

Year 2000heads

Year 2050heads

Conclusions• Volumetric approach: DOE assessment shows

more than adequate space– Free CO2 volume in structural and stratigraphic traps– Trapped CO2 residual phase

• Volume dissolved – Significance and rate uncertain

• Volume that can be stored beneath an area constrained by surface uses or by other unacceptable risks - What are key risks?

• Pressure limits as a limit on capacity – Similar volume to that used in volumetric approach 1.5 % of pore volume useful, increases with depth

• Displaced water as a limit on capacity – minor in large basins