Replacement of MEG with KHI for Hydrate Control in Subsea Flowline Offshore Myanmar

Abstract

Objectives/Scope This paper describes the successful replacement of Mono Ethylene Glycol (MEG) by Kinetic Hydrate Inhibitor (KHI) to guarantee flow assurance in the Shwe field subsea production system, offshore Myanmar. It covers the initial difficulties experienced with MEG, specific field conditions, the comprehensive KHI selection process and testing up to field application and operation. Methods, Procedures, Process MEG used for hydrate inhibition in the field's subsea flowline was originally regenerated in the topside facility, however contamination of the MEG with salts from formation water was causing process upsets. The option of installing a reclamation package presented many challenges and, after review of field conditions, the application of a KHI was considered as a promising alternative to MEG. With the engagement of specialist chemical suppliers a broad and challenging series of laboratory, as well as field tests, was carried out to select a suitable product. Finally a dedicated permanent injection skid was installed to guarantee stable KHI delivery and production. Results, Observations, Conclusions The difficulties caused by salt contamination of the MEG system, combined with the intricate field logistics at the remote site offshore Myanmar, entailed a speedy solution. This combined with suitable operating parameters of the field; i.e. low water content, high wellhead flowing temperatures, subcooling within known KHI operating range, ensured KHI was an economical solution. Nevertheless from desktop study to successful field application a series hurdles had to be crossed, including performance and compatibility tests, simulating all the expected Shwe Offshore Platform (SHP) operating conditions: Determination of Hydrate Equilibrium Temperature (HET); Induction Time Autoclave test for the required residence time in the presence of Corrosion Inhibitor (CI); Hot Injection ests at wellhead operating temperature; Thermal stability tests for topsides and condensate disposal system; Umbilical material compatibility tests; Compatibility of KHI with incumbent products (MEG and CI). Testing of a range of products, carried out by specialist chemical supplier, resulted in the selection of a qualified product, followed by a successful field application testing programme. Seven years after its introduction, KHI has helped achieve optimum field uptime and reduced operational costs as well as eased logistics constraints. Novel/Additive Information KHI is not new to the Oil & Gas industry, however information on its selection and application is not widely available. This paper sheds light on the steps to be considered when evaluating KHI as a suitable hydrate inhibitor, as well as the detailed laboratory tests for proper selection of a product. The intent is to help operators who are facing challenges with hydrate inhibition and could revert to KHI as an alternative.

Non-Amide Polymers as Kinetic Hydrate Inhibitors─Maleic Acid/Alkyl Acrylate Copolymers and the Effect of pH on Performance

“…KHIs can affect both the gas hydrate nucleation and crystal growth processes, delaying the build-up of gas hydrates for a length of time depending on the driving force (chemical potential) of the system. , KHIs have been shown to both increase the nucleation work required to form critical size nuclei and increase the effective number of sites where nucleation could occur . The driving force of the system is often described in terms of subcooling, but other factors including the absolute pressure must be taken into account. − There is evidence that KHIs can give total inhibition for an indefinite period up to a certain driving force …”