Innovative KHI Polymers for Gas Hydrate Control
Authors: Zheng Jun , Musa Osama , Lei Cuiyue , Zhang Yi , Alexandre Marc , Edris Scott A. 
Published: May 2011

This paper presents our recent laboratory development work on new kinetic hydrate inhibitors (KHIs) based on enhancements on Polyvinylcaprolactam (PVCap) chemistry. These newly developed KHIs are further modifications to PVCap polymer backbone by incorporating various functional monomers to achieve enhanced properties such as high precipitation temperature, salt tolerance, biodegradability, etc. Our lab test results indicated improved properties, such as higher injection temperature compatibility while maintaining similar KHI subcooling as commercial KHIs.

Historically, kinetic gas hydrate inhibitors based on PVCap chemistry has been used in the oil and gas field to prevent gas hydrate formation with good success. The PVCap-based KHIs sometimes encounter challenges in the field due to its relatively low cloud point, insufficient salt tolerance and biodegradability. These enhancements will allow broader applications of KHIs where extreme field conditions are encountered (e.g. high salinity and high injection temperature) and more environmental regulations (e.g. OECD 306 biodegradability) are enforced.

Our lab test results indicated significantly improved KHI properties of these new products. While one polymer exhibits excellent KHI performance under typical subcooling condition (e.g. 11.5°C) with high injection temperatures (&gt;85°C in 15% salt), the other polymer shows excellent biodegradability (OECD 306: &gt;60% in 28days) and inhibition performance. These enhanced features to conventional PVCap-based KHIs could greatly broaden potential field applications. Combinations of KHI/THI for much higher subcooling applications are also reported in this study. Use of KHI/THI combinations was shown to give long induction times (e.g. 8-12 days) under high subcooling (17.7°C) at much reduced total dosage levels than using THIs alone.

Development of these enhanced KHI products allows broader application of KHIs that can handle more demanding field conditions and more stringent environmental regulations. This will also allow use of less thermodynamic hydrate inhibitors (e.g. methanol or monoethylene glycol) for gas hydrate control in the oil and gas industry with significant CAPEX and OPEX savings.

Introduction

Gas hydrate formation is one of the most serious technical issues facing the oil and gas industry due to its potentially catastrophic nature that can lead to clogged and ruptured pipelines, loss of production time and potential injury to workers and damage to the environment. Gas hydrates are ice-like crystalline clathrate solids that form when small hydrocarbons (e.g. methane) are entrapped in the hydrogen bonded water cages with different structures (e.g. Type I, II).1,2 Elevated pressure and lower temperature as often encountered in offshore operations are the two driving forces for gas hydrate formation during oil and gas production and transportation. There are various approaches such as dehydration, heat management and chemical inhibition that have been successfully applied in the field to prevent and manage gas hydrates formation and to minimize potential risk to operations.1,2 Among these approaches, use of chemicals to prevent, delay and manage gas hydrates is widely used in the field with success. The chemical inhibitors can be generally categorized into thermodynamic hydrate inhibitors (THIs) and low dosage hydrate inhibitors (LDHIs).