An experimental Investigation on the Impact of Brine Composition on Silica Solubility at High Temperature 1 KHALED ELRAIES, AHMED FATAH, MOHAMMED AYOUB, 2 GAMAL GAAFAR 1 Petroleum Engineering and Geoscience Department, 2 PETRONAS Carligali Sdn. Bhd. Universiti Teknologi PETRONAS Tronoh, Perak MALAYSIA ahmed9fatah@gmail.com, khaled.elraies@petronas.com.my, abdalla.ayoub@petronas.com.my, gaafargr@petronas.com.my Abstract: - The theory of silica-water system or silica solubility is quite complex as it involves dissolution, polymerization and precipitation processes to form the silicate scale. The type and amount of silicate scale observed is dependent on several factors including pH, salinity, magnesium concentration, and the ratio of calcium to magnesium. This paper describes the impact of some factors including brine salinity and composition on silica solubility using crash quartz sandstone core samples. Synthetic brine with different salinities ranged between 20,000ppm to 60,000ppm were utilized to determine the change in soluble silica at 80°C. The amount of silica dissolved from the sandstone sample was measured using Silicomolybdate method and validated using Energy Dispersive X-RAY and X-RAY Diffraction techniques. The results clearly showed that the composition of the brine has a significant effect on the silica solubility. The amount of silica dissolution increased from 41.0mg/L to 67.8mg/L when the brine salinity increased from 20,000ppm to 60,000ppm, due to the increasing in salt contents of the brine. It was also observed that the addition of magnesium and calcium with ratio 1:1 to the brine would greatly affect the silica solubility. This has been confirmed by analyzing the samples before and after saturation by the use of Energy Dispersive X-RAY. Key-Words: - Brine Composition, Brine Salinity, Silica Dissolution, Silica Scaling, Silica Solubility, Water Flooding. 1 Introduction Silica is a general term, which refers to silicon dioxide in all of its crystalline, amorphous, and hydrated or hydroxylated forms. It commonly implies that the silicon content is given in terms of weight of silicon dioxide (SiO2) [1]. The common and simplest phase found in nature of silica is quartz, which is the main constituent of common sand [2], [3]. Many parts of the world including the western United States, Hawaii, Puerto Rico, Mexico, the Middle East and Southeast Asia have reported silicate scaling issues as one of the most severe problems that occurs due to silica water interactions. Silica poses several problems in all unit operations of the chemical recovery cycle i.e. evaporation, combustion and causticization [4]. Quartz is the most thermodynamically stable phase of silica [5]. The potential for silica scaling exists when the concentration of the dissolved silica exceeds the solubility limit at given temperature and pH [1], that results in the precipitation and deposition of amorphous silica, which once formed, is very difficult and costly to be removed [6]. The solubility of silica is dependent on many factors such as, pH, temperature, particle size, particle hydration and the presence of other ions like iron and aluminum [5]. In field applications; seawater –which has salinity ranged between 35,000 to 40,000ppm– is usually used for flooding operations. However, the salinity of the seawater is quite high which leads to the possibility of dissolving more silica ions. Basbar et al., [7] stated that silica dissolution ratio is increasing relatively with the increasing in brine salinity, when increased from 10,000ppm to 60,000ppm. Another fact is that the composition of the water is also affecting the silica dissolution, divalent minerals such as magnesium lead to the formation of magnesium silicate scale. Magnesium can bridge the colloidal silicate particles and form an amorphous magnesium silicate scale [8]. The silica scaling can also be found inside the production tubes, which leads to down-hole pumps failure, operational problems as well as a defect in pipeline systems [9]. There are numerous researchers declared that silica scale formation is a highly complex process, WSEAS TRANSACTIONS on ENVIRONMENT and DEVELOPMENT Khaled Elraies, Ahmed Fatah, Mohammed Ayoub, Gamal Gaafar E-ISSN: 2224-3496 90 Volume 12, 2016