Is there really enough space to “put it back”? 

Capacity Estimation for Geologic Storage of CO2

Susan Hovorka, Srivatsan Lakshminarasimhan, JP NicotGulf Coast Carbon Center

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

Amount of CO2 to be sequestered

• 7 x 109T/year US emissions from stationary sources

• If spread evenly over US:30 cm/year at @STP

0.4 mm/year at reservoir conditions

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Sources dot size proportional to emissions

Sinks color proportional to thickness

… and collect data on areal extent,thickness, porosity, and permeabilitythat permit simple estimates of storage capacity for CO2

Assessing CO2 Storage Capacity In Brine-bearing Formations

Identify a porous and permeable rock volume in the subsurface

…That is below underground sources of drinking water

…and isolated from them and from escape to the atmosphere by one or more seals

If preceding steps are favorable, proceed to additional steps, includingmatching to sources, estimating cost, permanence, and risk/uncertainly

How much?

Options for Estimating Capacity

• Total pore volume x Efficiency factor (E)– Volume in structural and stratigraphic traps– solubility trapped– residual phase

• 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 (Vatsan)• Displaced water as a limit on capacity (JP)

What do people want to know when they ask for storage capacity?

• How much will go in?– Volumetric

approach – current state of art

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

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

Reservoir Model Estimate Sweep Efficiency, Reservoir Volumetrics

• Model reservoir parameters as for hydrocarbons– Sand body

architecture– Petrophysics –

porosity, residual water saturation

– Input heterogeneity model sweep efficiency

• Unique elements– Rapid charge– Outside of trap– dissolution

PorosityFault planes

Sand/shale sequences

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

Capacity: Dissolution of CO2 into Brine –

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

HypothesisC

ap

acit

y

Heterogeneity

Seal

Low heterogeneity – dominated by buoyancy

Seal

High heterogeneity-poor injectivity

Seal

Just right heterogeneityBaffling maximizes capacity

Risk or Consequences Approach to Capacity

• How much will go in before unacceptable consequence occurs?

Capacity in a Geographically limited area

1-4

5-10

Well density

Closed Volume – Maximum Capacity May be Pressure Determined

Injection capacity

• Depth of formation• Injection pressure• Pore volume of formation

– Size of formation– Porosity

• Pressure gradientL

H

W

D

Vp = ΦV = ΦLWH

Injection Pressure and Depth

• Maximum injection pressure must be less than fracture pressure

• Fracture pressure estimated to linearly increase with depth of formation

• Fracture pressure in geo-pressure zone may increase non-linearly

Effect of Depth of formation

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

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 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

Effect of pressure gradient

• Ratio of injected to pore volume scales almost linearly with pressure gradient

• Scope for theory-based correlatory approach to estimating capacity

Fluid Displacement as a Limit on Capacity

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

• Unacceptable displacement of brine

Open Hydrologic System

Confined/Unconfined AquifersSpecific Storage - Storativity

• Unconfined (or water table) aquifer: dewatering pore space

• Confined (artesian) aquifer: rock matrix and water volume expansion

• Specific storage is a measure of how much water can be released from storage

• All we know about production can be applied to injection (~)

Domenico and Schwartz (1990)

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

HydraulicConductivity

(ft/day)

Storativity[-]

Year 2000heads

Year 2050heads

Outcrop is ImpactedYear 2050 drawdowns

ConclusionsLooking at large volumes of CO2 storage in pore space previously filled only with brine, we examined four combinations of boundary condition and risk avoided: Structural or stratigraphic trap: CO2 spills out

of trap Open  trap/volume: CO2 escapes from

volume Hydrologically closed basin: mechanical or

capillary entry pressure of seal is exceeded Hydrologically open basin: unacceptable

displacement of brine

Hydrograph from J-17 Well, Ft. Sam Houston

Graph shows water level oscillations from earthquake off west coast of Sumatra

9.0 magnitude on Richter Scale

Groundwater levels oscillated for 1 ½ hours with total amplitude of 2.6 feet

Quake occurred at 00:58 (UTC) on December 26

Courtesy of Geary Schindel Edwards Aquifer Authority