Formation Silicate Scale Inhibition during Alkaline Flooding: Static Model

Abstract

Abstract Scanning electron microscopy (SEM), X-RAY diffraction (XRD) and X-RAY Fluorescence (XRF) were employed to investigate the silicate scale during alkaline flooding. The formation of silicate scale is a multi-step process, involving silica dissolution, silica polymerization, and precipitation with other ions. It is a massive headache burdened to the oil and gas industry today. The aim of this study is to come out with a static model based on series of experiments to investigate the silicate dissolution ratio using quartz sand core samples. Synthetic brine with different salinities ranged from 5,000 ppm to 60,000 ppm and different alkali concentrations ranged from 0.4% to 1.2% were utilized to determine the change in soluble silica concentrations. In addition, two inhibitors; namely, Boric acid (BA) and Ploy Acrylic Acid (PAA) were screened and the optimum concentration for each inhibitor was identified. Based on the results from this experimental work, the silica dissolution ratio increased significantly with the increase in the the alkali concentration. The silica dissolution ratio increased from 1.1% at 0.4% alkali concentration to 4.6% with alkali concentration of 1.2 %. By introducing BA and PAA as inhibitors separately, significant improvement was observed in both cases. Using 50 mg/l of BA and PAA, 3.1% and 11.2% of the dissolved silica was inhibited, respectively. However, only 37.2% was inhibited when the BA concentration was increased to 350 mg/l, while 72% of the dissolved silica was inhibited when 350mg/l of PAA was utilized. The outcome from this research indicates that the best inhibitor does not prevent the silicate scale, but it might reduce it. This study may assist in understanding the mechanism of silica dissolution process and its effect against alkaline flooding.