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The Development of Novel Laboratory Test Method for Scale Inhibitor Evaluation in the Presence of Ferrous Iron

Product Number: 51320-14443-SG
Author: Haiping Lu, Zhenning Gu, Johnathon Brooks, Gina Beans, Stephen Heath, Daniel Bestgen, Dong Lee, Joe Penkala
Publication Date: 2020

Ferrous iron is typically present in the brines of oil and gas production. Soluble iron is considered to adversely affect the performance of scale inhibitors against calcium carbonate scale. However, it is particularly difficult to prevent the oxidation of ferrous iron to form ferric iron with even trace amounts of oxygen in laboratory testing conditions. The oxide species of ferric iron have less solubility than the ferrous iron, and ferric hydroxide may adsorb scale inhibitors on its surface. Therefore, the presence of ferrous iron in laboratory testing poses a challenge for evaluating its effect on scale inhibitor performance.  Recently, Kinetic Turbidity Test (KTT) has become a more recognized testing method for scale inhibitor evaluation. It is a novel laboratory test method using an Ultraviolet-Visible (UV-Vis) spectrophotometer to monitor the formation of scales at various dosages of tested products as a function of reaction time. In the presence of ferrous iron, in order to keep oxygen away from the ambient environment during the test, the instrument was placed into an anaerobic chamber for maintaining low level of oxygen environment (< 1 ppm O2 in the chamber) during the testing process. This paper presents the approach to conduct KTT in the present of ferrous iron, and compares the testing data with and without ferrous irons on scale inhibitor performance by KTT and anaerobic bottle testing for both calcite and calcium sulfate inhibition. The selected inhibitor chemistries include four different types of phosphonates (Phosphonate A, B, C, and D) and five polymer inhibitors (Polymer A, B, C, D, E). Results show that KTT provides an efficient and data-driven approach for evaluating scale inhibitor performance in the presence of ferrous iron. The mechanisms of scale formation and scale inhibitor performance under the effects of iron were discussed. This paper provides insight for scale treatment chemistry and dosage in the presence of iron.