Stable Isotope Geochemistry

Stable isotopes are used in CCS to look for leakage of CO2 into overlying

aquifers or into the surface environment

What are Stable Isotopes

• These are isotope that do not decay over time as the radiogenic isotope do.

• They fractionate (change composition) based on geological processes.

• The light stable isotopes include H, C, O, S• In CCS, carbon isotopes are the most common

to be used because it can be a tracer for CO2

• We will focus this discussion on Carbon isotopes.• In order to understand them we need to look at:

– Terminology– Ranges of natural values– Fractionation processes

• Examples of carbon isotopes in CCS

Carbon has two stable isotopes, 12C and 13C, and one radioactive isotope, 14C. Carbon isotope ratios are measured against Vienna Pee Dee Belemnite (VPDB).[2]

Positive δ13C values mean that the sample has a higher 13C/12C ratio than the standard. We casn say it is enriched in 13C relative to the standard Since it has more heavy isotope it sometimes called heavy. But this is a relative term, and heavy and light can be used to compare two substance whose delta value is known. Negative δ13C values mean that the sample has lower 13C/12C ratio than the standard.

We measure isotope ratios rather than absolute amounts because we can do that more easily and precisely.

Definition of (delta)

3

Std

Samp3

Std16

18

Samp16

18

18 101R

R10x1

O

O

O

O

‰O

Fractionation Factor• Any two phases (gas, liquid,

solid) at equilibrium will not have the same isotopic ratios.

Therefore α will not be equal to 1.

• It is however close to one reflecting the small changes in isotope ratios that we can measure.

• Fractionation is a function of temperature. It decreases as temperature rises.

RR

y

xxy

So calcite that is being deposited from bicarbonate in solution will have a carbon isotopic composition that is controlled by the aqueous bicarbonate and the temperature of deposition.

31.3T/1034.3ln10 26OHqtz

3

2

Carbon stable isotopes are fractionated primarily by photosynthesis (Faure, 2004). During photosynthesis, organisms using the C3 pathway show different

enrichments compared to those using the C4 pathway, allowing us not

only to distinguish organic matter from abiotic carbon, but also what type of photosynthetic pathway the organic matter was using.[1]

http://www.isoforensics.com/images/425_C3_v_C4_plants.jpg

Isotope values of different carbon reservoirs.

• http://www.seafriends.org.nz/issues/global/global35.gif

hydrogen and oxygen isotopes in water

Isotope Tracing of CO2 Seepage: Controlled Release Experiment in Bozeman, MT

J. Fessenden1, K. Gullickson2, H. Rauch3, L. Dobeck2, W. Pickles4, J. Jacobson4, L. Spangler2;

CO2 was injected into a pipe at a depth of 2.5 meters and allowed to leak out into the soil to simulate a leak

Soil Gas analysis

CO2 release started 7/9/07

On-site isotope monitoring, a new marketing niche

Schematic of SACROC Study Area

From Romanak

End member ∂13C Range

Injectate CO2 gas 0 to -6

Microbial CO2 gas -23 to -29

Carbonate -2 to -8

Dockum Water -4 to -13

Permian water -8 to -10

Produced water +1 to +9

Normal degassing

1. constant PCO2

2. decreasing PCO2

Gas input

1. injectate

2. microbial

CO2 Source Identification Measurements from SACROC

From Romanak, Texas Bureau of Geology

Isotope Modeling ResultsNon-unique solution.

Data can be explained by natural processes.

General microbial trend.

From Romanak, Texas Bureau of Geology

EPNG Com A 300

Howell D 351 Howell D 350 S

EPNG Com A 300S Howell D 353

Howell A 300 Howell A 301S

FC State Com1

Howell D 352 S

Howell G 300

Picture courtesy to ARI and ConocoPhilips.

Objectives:

Tracking CO2 movement and determining ultimate fate of injected CO2.

Investigation of long-term storage mechanism of geological formation and

identification of CO2-rock, CO2-fluid-rock interactions

Investigation of potential impact on the receiving environment.

Northeast

Southwest

Injection

From: L. Li, PRRC

0 5 10 15 20 2520

21

22

23

24

25

26

27

28

29

30

Howell A #300

Howell A301

Howell A301S

Howell D #351

Howell D350S

Howell D 352

Howell D #352S

Howell D 353

Howell G300

FC State Com #1

EPNG Com A #300S

EPNG Com A 300

month

d1

3C

Injection

13C Isotope

0 5 10 15 20 25

25-

20-

15-

10-

5-

0

Howell A #300

Howell A301

Howell A301S

Howell D #351

Howell D350S

Howell D 352

Howell D #352S

Howell D 353

Howell G300

FC State Com #1

EPNG Com A #300S

EPNG Com A 300month

d1

8O

Injection

18O IsotopeFrom: L. Li, PRRC

The calculations assumed reaction in a closed system where CO2 is allowed to interact with varying masses of either a HCO3- bearing brine, calcite or hydrocarbon-rich rock (HC; LostHills, CA) of unspecified composition. Equilibrium isotope fractionation (fractionation factors taken from Friedman and O’Neil(15)) was assumed in all calculations except one set where we used experimental batch-sorption isotope partition data obtained at ORNL on Lost Hills core.

Experimental Geochemical Studies Relevant to Carbon SequestrationJames G. Blencoe , David R. Cole, ,Juske Horita Geochemistry GroupChemical and Analytical Sciences Division Oak Ridge National Laboratory

Isotope values of different carbon reservoirs.

• http://www.seafriends.org.nz/issues/global/global35.gif

δ13C values of ocean reservoirs

http://web.me.com/uriarte/Earths_Climate/Appendix_6_files/p247.jpg

Carbon isotopes can also be used as direct measures of injected CO2. 13C is a stable isotope whose concentration, relative to 12C, varies with the source of carbon.

Marine Sequestration: Monitoring

Based on the measured ambient variability and measurement precision of 13C , slightly lower dilutions (~3x105) can be resolved using natural 13C. The ambient variability of 13C needs to be checked during the actual survey.

A flow system to deliver the CO2 from the supply ship, through the coiled tubing, to depths of 800m at a steady flow.

INTERNATIONAL COLLABORATION ON CO2 SEQUESTRATION Annual Report Reporting Period: August 23, 2000 - August 23, 2001Principal Authors: Howard J. Herzog and E. Eric Adams