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, 12 C and 13 C, and one radioactive isotope,stable isotopes 14 C. Carbon isotope ratios are measured against Vienna Pee Dee Belemnite (VPDB). [2] 14 CBelemnite [2] Positive δ 13 C values mean that the sample has a higher 13 C/ 12 C ratio than the standard. We casn say it is enriched in 13 C 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 δ 13 C values mean that the sample has lower 13 C/ 12 C ratio than the standard. We measure isotope ratios rather than absolute amounts because we can do that more easily and precisely.

Definition of  (delta)

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. 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.

Carbon stable isotopes are fractionated primarily by photosynthesis (Faure, 2004).photosynthesis During photosynthesis, organisms using the C 3 pathway show different enrichments compared to those using the C 4 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]C 3 pathwayC 4 pathway [1]

Isotope values of different carbon reservoirs.

hydrogen and oxygen isotopes in water

Isotope Tracing of CO 2 Seepage: Controlled Release Experiment in Bozeman, MT J. Fessenden 1, K. Gullickson 2, H. Rauch 3, L. Dobeck 2, W. Pickles 4, J. Jacobson 4, L. Spangler 2 ; 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 CO 2 gas 0 to -6 Microbial CO 2 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 CO 2 Source Identification Measurements from SACROC From Romanak, Texas Bureau of Geology

Isotope Modeling Results Non-unique solution. Data can be explained by natural processes. General microbial trend. From Romanak, Texas Bureau of Geology

EPNG Com A 300 Howell D 351Howell 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 CO 2 movement and determining ultimate fate of injected CO 2. Investigation of long-term storage mechanism of geological formation and identification of CO 2 -rock, CO 2 -fluid-rock interactions Investigation of potential impact on the receiving environment. Northeast Southwest Injection From: L. Li, PRRC

Injection 13 C Isotope Injection 18 O Isotope From: 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 Sequestration James G. Blencoe, David R. Cole,,Juske Horita Geochemistry Group Chemical and Analytical Sciences Division Oak Ridge National Laboratory

Isotope values of different carbon reservoirs.

δ 13 C values of ocean reservoirs

Carbon isotopes can also be used as direct measures of injected CO C 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 (~3x10 5 ) 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, August 23, 2001 Principal Authors: Howard J. Herzog and E. Eric Adams