A laboratory study on pteroyl-l-glutamic acid as a scale prevention inhibitor of calcium carbonate in aqueous solution of synthetic produced water

Oil well scale inhibition with green scale inhibitor is a relatively unexplored area. A huge amount of produced water containing various types and amount of residual scale and corrosion inhibitors is discharged into the environment everyday, which has brought focus of environment regulatory bodies and encourages operators to look for greener chemicals. Pteroyl-l-glutamic acid (PGLU) is a type of water soluble vitamin M that widely exists in nature and has an excellent environmental profile, such as high biodegradation potential and nontoxic. Although it is acidic, it prevents corrosion through passivation of steel surface through chelating mechanism. This specific property has encouraged us to further investigate its scale inhibition efficiency.Three different synthetic produced water (SPW) solutions were prepared having formation water (FW)/sea water (SW) ratio of 70:30, 50:50 and 30:70. The mixed waters were prepared just before the test and pH was adjusted to 7.2 with CO2 flow. Static jar tests with different SPW and at different temperatures were conducted for preliminary qualification and dynamic flow tests were conducted to determine minimum inhibitor concentration (MIC) requirement at well intake temperature. Static and dynamic studies show that PGLU could be a potential scale inhibitor for produced water with high scaling tendency, tested up to 110 °C for an offshore reservoir fluid chemistry. Characterization of inhibited scale crystals through various methods (FTIR, XRD and SEM) revealed structural deformation of crystals which explained scale prevention mechanism. The study suggested that PGLU is an excellent green chemical, for continuous injection into the wellbore below bubble point region for controlling carbonate scale.