A universal scale inhibitor: A dual inhibition/dispersion performance evaluation under difficult brine stresses

Abstract

Scale inhibition is of crucial importance in harvesting geothermal energy, an attractive, renewable and sustainable energy source. The majority of the geothermal reservoir waters around the world contain a variety of anions and cations, which are prone to inorganic precipitation when subjected to drastic changes in both temperature and pressure, causing failures and unwanted shut-downs. Our goal is to prevent the formation, precipitation and deposition of such scales by stabilizing their respective components. Herein, the ability of a methacrylate-structured, grafted co-polymer, coined PEGPHOS-LOW (with polyethylene glycol and phosphonate grafts), to control inorganic precipitation is evaluated for four artificial geothermal brines of variable scaling propensity towards common geothermal scales, such as amorphous silica, magnesium, aluminum and iron silicates, zinc, lead and iron sulfides and calcium carbonate. Inhibitor selection was based on previous results obtained with four, similar inhibitor grafted co-polymers (one containing only polyethylene glycol, PEG, one with only phosphonate grafts, and two containing variable ratios of both grafts) against individual scales. The working brines were designed based on the saturated conditions of geothermal well fluids. PEGPHOS-LOW is a polymer that contains 34 PEG20 grafts, and 14 phosphonate grafts. It is a dual scale control additive, as it can function both as a scale inhibitor (keeping the scaling species soluble) and as a dispersant (keeping the scale particles formed in a suspended form). It displays a dosage-dependent scale inhibition and dispersion behavior, however, very high concentrations are necessary for satisfactory effectiveness, due to the high scaling propensity of the brines.