The Impact of Organic Acid on Scale Inhibitor/Corrosion Inhibitor Interaction, a Case Study from West Africa

摘要

A development in deepwater off Western Africa has been experiencing incompatibility between the incumbent scale inhibitor and a newly deployed corrosion inhibitor. Initial laboratory testing to determine the amount of scale inhibitor necessary to overcome the interference from the corrosion inhibitor indicated that the effects of the corrosion inhibitor could not be overcome by increasing the dose of the scale inhibitor. Testing of other scale inhibitors indicated that there was not a suitable scale inhibitor that could inhibit scale formation in the presence of the corrosion inhibitor. That initial work was performed using synthetic brines that contained no acetate/acetic acid buffer to help control pH of the system. Further work evaluating the effect of buffering upon scale inhibitor performance employed brine containing an acetate/acetic acid buffer. Once this buffer solution was employed in static bottle testing, it was observed that an alternative scale inhibitor previously tested now worked in the presence of the corrosion inhibitor. While it is known that corrosion inhibitors can impact scale inhibitor performance the impact of organic acid on this interaction has not been published. Since the field where the chemicals were to be applied is known to contain organic acids (upwards of 2,000 ppm), the testing which included the acetate/acetic acid buffer is viewed as a more representative test for the field than the testing that did not contain any organic acids. A field trial of the alternative scale inhibitor and the corrosion inhibitor has been under taken. The paper will present the results from two field trials, the laboratory evaluation to understand the mechanism of interaction and selection of the alternative inhibitor chemical. This paper will shed light on the challenging subject of scale inhibitor and corrosion inhibitor interaction and review the most appropriate test methods/conditions to select non interfering chemicals.