FT-IR and Raman Spectroscopic Characterization of the Major Oilfield Sulfate Scale Forming Minerals

Abstract

Sulfate minerals commonly form in the oilfield environment due to secondary recovery operations. Two essential tools for identification of these minerals are Fourier transform infrared (FT-IR) and Raman spectroscopies. In this paper, a comprehensive database of the FT-IR and Raman spectra of these minerals has been composed. The symmetry of the sulfate tetrahedra in the various sulfate molecules has been assigned from observation of the vibrational degeneracy. Force constant calculations show that cation mass and polarizability are the dominant influences upon sulfate symmetry. Studies of the vibrational peak positions have demonstrated a direct relationship between properties of the associated sulfate cation and the positions of both the infrared and Raman v1 and v3 vibrations. The major influences were found to be cation electronegativity, cation mass, and cation ionic radius. These observations were confirmed from force constant calculations. It has been concluded that both FT-IR and Raman spectroscopies are valid techniques for identification of oilfield scale minerals. Raman spectroscopy is particularly useful as it can be applied to aqueous systems and the in situ measurements of scale formation.