Detection of Soluble Ligand-Tuned Molecular Tags for Subterranean Fluid Flow Monitoring Using Resonance Raman Spectroscopy
Our team has investigated a series of soluble coordination complexes for use as tags to monitor underground fluid flows in reservoirs. While most of the metal-ligand (M-L) complexes were based on the dianionic salen family of ligands, conceptually other ligands such as porphyrins or phthalocyanines could be used with similar success. Detection and identification of these species in solution were performed by inductively coupled plasma (ICP) or Raman/resonance Raman (rR) spectroscopy. The preparation of a large number of new M-L salen complexes was accomplished. Complexes were prepared that were soluble in either water or hydrocarbons to allow for flexibility in use. Unambiguous identification of these complexes allowed for meaningful molecular dynamics (MD) calculations to be performed, so that the attraction of the M-L complexes to either the rock formation or the liquid media could be evaluated. The use of soluble M-L species was found to avoid issues of rock deposition.