Abstract

A dual functional kinetic hydrate inhibitor (KHI) and compatible corrosion inhibitor (CI) package was developed to simplify production chemistry demands for operation in wet gas mode. As these two classes of chemistries are both water soluble and contain surface active components, they have a tendency for interference reducing the efficacy of each inhibitor. Their pairing in a production scenario requires both comprehensive performance testing as well as extensive secondary properties evaluation.

The KHI is to serve as a traditional KHI during steady-state operations while performing as a thermodynamic hydrate inhibitor (THI) during extended shut-ins and cold well restarts. This challenge required the development of a KHI which would retain performance upon significant dilution in a thermodynamic hydrate inhibitor solvent carrier (methanol, ethanol, monoethylene glycol, etc). Performance of this new KHI would be confirmed in blind rocking cell experiments, in the presence of the matched corrosion inhibitor, targeting a hold time of more than eight days at a subcooling of 8 ºC.

The CI is targeted to reduce the general corrosion rate to less than 0.1 mmpy and prevent localized attack. Due to the surfactancy of this class of chemistry, the tendency to induce and stabilize emulsions is of high concern. A robust formulation amenable to modification and potential dilution is required to address the application of chemical over a vast subsea network containing wells of varying age, existing infrastructure, production profiles, and operating conditions.

This paper describes the development, qualification process, related lessons learned, and field applications of this new KHI/CI package.

Introduction

The oil and gas industry often relies on chemical solutions to address challenges related to flow assurance and corrosion inhibition. The transport of produced fluids containing water and acid gases such as carbon dioxide and/or hydrogen sulfide in metal pipelines afford conditions susceptible both to gas hydrate formation and corrosion. Accordingly, production chemical strategies typically must consider a compatible corrosion inhibitor and low dosage hydrate inhibitor as a unified package.

Standard chemical compatibility often includes the mixing of two neat production chemicals with exposure at various temperatures to examine for hazing, phase separation, precipitation, etc. This exercise provides operators insight in the event that chemicals are accidently mixed in storage tanks or may come into contact in delivery lines. Though, the performance compatibility of a KHI and a CI presents a more challenging case.

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