Silicate scaling during high pH Alkaline Surfactant Polymer (ASP) flooding is known to adversely affect oil production. The silicate scale occurs as a result of the dissolution of silicates under high pH conditions and where the fluids subsequently flow into a region of lower pH where they then precipitate. The precipitation of magnesium silicate strongly depends on solution pH and temperature and is affected by the kinetics of the silicate scaling reaction.
In this paper, the effect of pH on the stoichiometry and morphology of silicate scale is studied. A range of spectroscopic techniques, including Environmental Scanning Electron Microscope/ Energy Dispersive X-Ray Spectroscopy (ESEM/EDX), Fourier Transform Infrared (FTIR) and X-Ray Powder Diffraction (XRD) are applied in order to analyse the precipitated silicate scales in the laboratory. These spectroscopic techniques, when used along with reference sample spectra, yield a number of interpretive clues as to the nature of the silicate precipitates which are formed. The further analysis of the solution and precipitate by Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES) and ESEM/EDX also gave complementary information which was consistent with the results obtained from the other spectral methods above.
The approach used in this work has enabled us to establish the composition and morphology of the silicate scales formed under different pH condition. There is relationship between the pH conditions and the compounds appearing in the precipitate. Results obtained can be used to help determine the most appropriate type of scale inhibitor for silicate scale mitigation in future.