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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