The development of a test methodology and new findings in silicate scale formation and inhibition

Abstract

Silicate scale is a well-known problem associated with certain EOR methods such as Alkaline Surfactant Polymer (ASP) Flooding and Thermal Oil Recovery. The kinetics of this silicate scale formation during ASP flooding is poorly understood due to the complexity of the (several) reactions that occur simultaneously and the strong dependency of these reactions on a range of factors in the reservoir. An experimental methodology has been developed in this work to produce a well defined silicate scale in the laboratory. This has then been used in silicate inhibition efficiency experiments in order to study potential silicate inhibitors/dispersants. The produced silicate scale has been studies using elemental analysis for Mg and Si (by ICP) to quantify the severity of silicate scaling. In addition, the precipitated silicate deposits have also been examined using several spectroscopic methods such as ESEM/EDAX, FTIR, and XRD. A number of specific aspects of silicate scaling are studied in this thesis, as follows: (i) silicate scale formation and the related mechanisms of inhibition by chemical scale inhibitors (ii) the sensitivities of silicate scaling to various factors such as pH, temperature, initial Si:Mg molar ratio and brine ageing, (iii) the development of experimental methodology to study the effect of ferrous ion in reducing environments, and (iv) the effect of ferrous iron in the formation and inhibition of silicate scale. These studies have enabled us to develop some new insights into the mechanisms of silicate scale formation and inhibition. The experimental methodology developed proved to be repeatable and reproducible. Results from the application of various spectroscopic methods enabled us to establish the morphology of the silicate scale formed and its stoichiometry in terms of the Si:Mg molar ratio. Factors governing the formation of silica and metal silicate in aqueous systems were studied and evaluated by establishing the types and morphology of the silicate precipitates produced using spectroscopic analysis and by measuring the Si:Mg molar ratio. It has been demonstrated that the amorphous silicate scale can be inhibited using the tested inhibitor A5 (and this has an MIC of ~ 50ppm); and how various functional groups affect IE % of silicates. An anaerobic experimental methodology was developed in this work and it is shown that the ferrous iron does enhance the silicate scale formation and the Fe itself is fully incorporated into the silicate scale which is formed that degrades the performance of the silicate inhibitors studied.