SS FA- Why Use Kinetic Hydrate Inhibitor
Authors: Alapati Rama R. , Sanford Elizabeth Aubray , Kiihne Eric , Vita E. 
Published: July 2010

A number of gas fields have been developed in the Middle East, Offshore Western Australia and in the Asia-Pacific region for the last five years as the demand for Liquefied Natural Gas (LNG) has grown tremendously worldwide. Most of these gas field production systems consist of long subsea flowlines, which are flowing with three phase fluids gas, condensate and water. The cold temperatures of the subsea environment pose a flow assurance risk to production, especially for hydrate blockages.

The only solution currently being considered to address the risk for hydrate blockages in gas fields is the usage of Kinetic Hydrate Inhibitors (KHIs), not Anti-Agglomerate Low Dose Hydrate Inhibitors (AAHIs). The most significant production concern for all producers associated with this production scenario is that the performance of the KHI is compromised in the presence of the Corrosion Inhibitor (CI). The reason for not considering the AAHIs for this application, whose performance is not compromised by the corrosion inhibitor, is the general belief that these chemistries are predominantly water soluble and therefore increase the toxicity of the produced water.

The published literature to-date is focused on understanding the interactions between the KHI and the CI chemistries to solve the incompatibility issue. The lack of literature to-date showcasing the success of such an understanding warrants a solution with a different perspective. Data is available for new generation chemistries currently being used in the industry that show greater than 99% oil solubility and would hence overcome the toxicity concern that was valid for the first generation AAHI chemistry.

This new generation chemistry was tested by Heriot-Watt University in the United Kingdom (UK) that shows the product effectiveness up to 90% water cut at a reasonable subcooling, applicable for these subsea flowlines in discussion. The performance at these high water cuts will make this new generation chemistry more applicable for these subsea flowlines without the risk of hydrate blockages.

Introduction

Gas hydrates are solid inclusions that are similar to ice in appearance but differ in structure. Under certain conditions of high pressure and low temperature, water physically entraps the molecules of a hydrate-former inside a hydrogen bonded solid lattice. Hydrate-formers include nitrogen, carbon dioxide, hydrogen sulfide, methane, ethane, propane and butane and are the main components of natural gas (Makogon 1998; Sloan 1998). Gas hydrates are not stable at ambient temperature and pressure. Hydrate agglomerationss can be even formed with low concentrations of water.

To protect a system against gas hydrate formation, the right chemical at the right dose rate needs to be injected into the system. Currently there are two mechanisms of low-dose hydrate inhibition available as an alternative to Thermodynamic Hydrate Inhibitors (THIs); Anti-Agglomerate Hydrate Inhibitors (AAHIs) and KHIs. The AAHIs and KHIs are normally classified as Low Dosage Hydrate Inhibitors (LDHIs).