Hydrogen & Oxygen isotopes of water
Correlation of formation waters in reservoirs and determination of potential diagenetic modification of reservoir rocks. Various exchange processes between water and minerals can affect the isotopic composition of formation water.
These isotopic analyses are performed at the IFE laboratory in Kjeller.
Oxygen isotope analyses
H2O(l) is equilibrated with CO2(g) at 30°C for 24 hours, whereupon the δ18O composition of CO2 will reflect that of the original water sample. Impurities are separated from CO2 on a Poraplot GC column before on-line determination of δ 18O, using a Thermo DeltaXP isotope ratio mass spectrometer.
Hydrogen isotope analyses
H2O(g) is reduced with Zn(s) to H2(g) and ZnO(s) in sealed, evacuated quartz vessels at 900°C. The δD composition is determined by a Horizon isotope ratio mass spectrometer from NU-Instruments.
Inferences of reservoir rock diagenesis can be adversely affected by:
- Lack of knowledge of parent meteoric water isotopic composition, which is affected by the balance between evaporation and precipitation and temperature at the time of formation
- Unknown fractionation processes, which can include evaporation in petroleum reservoirs above ~80°C.
- Contamination by fracturing fluids.
Clayton R.N., Friedman I., Graf D.L., Mayeda T.K., Meents W.F., Shimp N.F. (1966) The origin of saline formation waters: 1. Isotopic composition. Journal of Geophysical Research 71, 3869–3882.
Ferronsky V.I., Polyakov V.A. (2012) Isotopic composition of formation waters. In: Isotopes of the Earth’s Hydrosphere. Springer, Dordrecht.