It sounds like a "whodunnit" and IT IS! The mystery: there is water in our oil or gas well, but from where did it come?! Recent advances in isotope geochemistry can help solve the case. It is yet another application of Isotope Forensics. These techniques take advantage of the fact that even atoms of the same element may have slightly different weights and exhibit slightly different thermodynamic and kinetic behavior. These differences can identify the plants used in making a specific piece of paper or tell the exact location from which a drop of rain water originated.
Applying these findings to the oil and gas production field; by for example, analyzing produced water with an Isotope Ratio Mass Spectrometer, can determine whether all the produced water originates in the same formation or whether there is some migration of water from different geologic zones or formations. The advantage of isotope forensics is that we are analyzing oxygen and hydrogen atoms from the water itself. We do not need to relay on adding dyes or introduced isotopes in order to trace the source of the water. Strontium Isotopes, which vary as to geologic time period, can also be used to identify the source formations of either production, or migratory, oil and gas.
Such information can be important in addressing production problems such as determining suitable strategies to prevent water infiltration into a production zone. Of course, it can also be useful to address environmental concerns such as tracking the source of seepage or the adulteration of groundwater.
Yet another application follows the theory that Heavy Oil is the result of advanced biodegradation. Thus the viscosity of heavy oil is related to the period of biodegrading experienced by the deposit. Biodegradation produces systematic compositional changes including isotopic variations. N-alkanes are preferentially removed and iC4/nC4 ratios increase and δ13C2 and δ13C3 increase. Thus, isotopes in natural gas can be used to map out heavy oil reservoir “sweet spots”.
In short; fluids can run, but they can't hide. Isotope forensics can identify them as surely as does a human fingerprint, allowing us to track them to their origin over space and time.