Low-Adhesion Coatings Provide Novel Gas-Hydrate-Mitigation Strategy

Abstract

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper OTC 27874, “Low-Adhesion Coatings as a Novel Gas-Hydrate-Mitigation Strategy,” by Erika Brown, SPE, Sijia Hu, Shenglong Wang, and Jon Wells, Colorado School of Mines; Matthew Nakatsuka and Vinod Veedu, SPE, Oceanit Laboratories; and Carolyn Koh, SPE, Colorado School of Mines, prepared for the 2017 Offshore Technology Conference, Houston, 1–4 May. The paper has not been peer reviewed. Copyright 2017 Offshore Technology Conference. Reproduced by permission. When certain thermodynamic conditions exist in oil- and gas-production flowlines, gas-hydrate plugs can form and greatly restrict flow. One potential strategy for hydrate management involves allowing hydrates to form but mitigating their ability to deposit on the flowline walls by deploying a low-adhesion, protective surface coating on the inside wall of the flowline. In this study, two coatings were produced and evaluated to determine their effect on hydrate adhesion onto carbon-steel surfaces. Introduction In order to test the adhesion of hydrates to the two low-surface-energy coatings, micromechanical-force (MMF) apparatuses were used at low and high pressures. MMF apparatuses have been used historically to investigate both hydrate/hydrate interparticle forces and hydrate/surface interactions. The primary mechanism of hydrate cohesion and adhesion has been determined to be capillary bridging. Many of the parameters in capillary bridge theory can be altered through the modification of the system (e.g., the addition of surfactants or other chemicals or modification of the hydrate or solid sur-face). Hydrate/surface interactions have been studied previously; however, the surfaces used in these previous adhesion studies were always either stainless-steel or mineral surfaces, such that surface degradation by corrosion was not taken into account. In addition to MMF studies measuring adhesion forces, experiments were performed in a rocking cell to observe more-macroscopic effects of the coatings on deposition. Rocking-cell tests give a simulated flow environment and may provide insight into how the coatings respond in the bulk, rather than single-particle measurements performed with an MMF apparatus. Materials An omniphobic-coating system was developed to protect metallic surfaces against corrosion and accumulation of oil and gas precipitates such as carbonate and sulfide scales. The coating consists of a composite polymer coating that provides a low-interfacial-energy exterior with a fixed base that is impermeable to both water and olefin phases. By acting as a barrier to wetting and chemical contact with the protected surface, this coating provides protection against extreme acidic and basic chemicals and limits pitting corrosion in oxygenated and anaerobic carbonic acid environments. Additionally, the low-surface-energy exterior minimizes wetting, reduces drag/turbulence in mixed flows, and limits any surface features that could act as nucleation sites for precipitate formation and adhesion.