(44d) Assessing the Performance of a Kinetic Hydrate Inhibitor Using a Crystal Hydrate Inhibition (CGI) Method for a Gas and Gas-Condensate System

Gas hydrate formation in oil and gas pipelines is a complex process spanning space and time dimensions across multiple scales. At the micro/meso-scopic scales, (heterogeneous) nucleation and growth occurs. During nucleation, the first hydrate proto-nuclei (clusters) are formed, which, after some time ‘induction time’, can grow to produce detectable macroscopic crystals. Then, hydrate crystals may agglomerate, potentially forming a plug in the pipeline.

One of the methods to manage hydrate formation is the injection of Kinetic Hydrate Inhibitors (KHIs). The accepted understanding is that KHIs slow down or interfere with nucleation, hence extending the induction time. KHIs are normally evaluated by measuring induction times in the laboratory. However, quantifying induction times is problematic as nucleation is inherently stochastic, meaning measurements are often poorly repeatable with such studies time-consuming. Furthermore, it is often mistakenly believed that when a hydrate crystal has been detected in a KHI inhibited system, the KHI has ‘failed’.

Recent research has proven that KHIs are not only nucleation delayers but also powerful crystal growth inhibitors. In view of this, a Crystal Growth Inhibition (CGI) method [1,2] for the reliable evaluation of KHIs has been previously developed. This method shows that KHIs induce a number of well-defined hydrate crystal growth inhibition (CGI) regions with different growth rates as function of subcooling. This new methodology provides a useful decision-making tool in order to manage the uncertainty of KHI performance during the different phases of real field production operations [3].

In this contribution, we present the results of an extensive experimental programme utilising the CGI method for the qualification of a commercial KHI that will be implemented in a greenfield development in the North Sea.  

[1] Anderson et al. (2011) Development of a crystal growth inhibition based method for the evaluation of kinetic hydrate inhibitors, 7^thIntl Conference on Gas Hydrates

[2] Anderson et al. (2011) Application of a new crystal growth inhibition based KHI evaluation method to commercial formulation assessment, 7^thIntl Conference on Gas Hydrates

[3] Luna-Ortiz et al. (2013) Fast-track flow assurance design for kinetic hydrate inhibitors without laboratory testing: A case study, in 16^th Intl Conference on Multiphase Production Technology