The 6th phase of our Low Dosage Hydrate Inhibitors JIP, onging since 2002, began on the 1st May 2018 for 3 years. It is currently sponsored by TOTAL, Equinor and Nalco-Champion.

New sponsors are welcome and can join at any time during the phase.

An outline of the project is given below.

2018-2021 Phase: Gas Composition & Structural Controls on Hydrate Plugging & Low Dosage Inhibition / Towards Greener LDHI Solutions

In previous project phases, a novel crystal growth inhibition (CGI) method was developed for KHI evaluation which, in contrast to traditional stochastic induction time tests, yields repeatable and transferable results. In-depth JIP CGI studies have since provided a unique insight into KHI mechanisms, highlighting the importance of gas composition, hydrate structure and pressure on performance, in addition to yielding robust data on the generic effects of other pipeline chemicals (MEG, MeOH, condensate…), acid gases (H2S, CO2) and pH [1-6]. The CGI method has greatly improved operator confidence in KHIs, dispelling common myths which previously restricted usage, and is now considered industry standard.

While significant advances have been made for KHI evaluation, industry hydrate transportability / AA testing remains disparate, suffering from a lack of standardisation and persistent gaps in knowledge of the generic fundamentals involved. As a result, the use of anti-agglomeration as a hydrate mitigation strategy – be that by chemical AA treatment or utilising natural transportability properties – is still restricted. Historically, the focus of transportability studies has been liquid water and oil phases, with little consideration given to the gas. However, recent novel JIP work shows gas composition to be a major factor. Rather than just a single ‘natural gas hydrate’ (e.g. s-II) forming, multiple hydrate phases of differing composition/structure nucleate and grow as subcooling is increased, including an all but unknown low pressure s-II methane hydrate. Furthermore, subsequent, often highly thermal, solid-solid transitions between structures seemingly play a key role in sudden, problematic agglomeration at low hydrate fractions, with this being strongly gas composition dependent. The same (reversible) processes also apparently give rise to novel ‘un-agglomeration’ behaviour, where plugging consistently disintegrates at fixed PT, sometimes well inside the hydrate region. Ranked as top priority by sponsors, investigation of this topic will form the core theme of the proposed new 3-year phase, with the aim of advancing anti-agglomeration strategies, standardising lab testing, and reducing operating risks/costs.

While the primary focus for the proposed new phase will be anti-agglomeration, KHI R&D will continue to form a significant component of work. Sponsor prioritised topics here include gas composition / structural controls on KHI inhibition & induced dissociation, hydrate fraction tolerance ‘thresholds’, and inhibition of hydrates preformed in the absence of KHIs (e.g. top of line hydrates), with associated work on the effect of other pipeline chemicals (e.g. salts, liquid hydrocarbons, MEG/methanol) as appropriate.

Finally, as traditional LDHI chemistries have both toxicity (AAs) and biodegradability (KHIs) issues, tightening environmental regulations mean there is an increasing need for greener alternatives. The project will therefore continue to fast track these.

Having proven the good functionality of least one commercial Bio KHI, work will focus on enhancing the performance of this, trialling any new candidates, and evaluating some emerging green AAs.

Contact Details

For further information, please contact:

Ross Anderson
Institute of GeoEnergy Engineering
Heriot-Watt University
Edinburgh EH14 4AS, UK
Tel: +44(0)131 451 3564
E-mail: ross.anderson@hw.ac.uk
Bahman Tohidi
Institute of GeoEnergy Engineering
Heriot-Watt University
Edinburgh EH14 4AS, UK
Tel: +44 (0)131 451 3672
E-mail: bahman.tohidi@hw.ac.uk

References

[1] Anderson, R., Mozaffar, H., and Tohidi, B. “Development of a Crystal Growth Inhibition Based Method for the Evaluation of Kinetic Hydrate Inhibitors”, Proceedings of the 7th International Conference on Gas Hydrates, Edinburgh, Scotland, United Kingdom, July 17-21 (2011).

[2] Bourg, P., et al., “Selection of Commercial Kinetic Hydrate Inhibitors using a New Crystal Growth Inhibition Approach Highlighting Major Differences between Them”, SPE Middle East Oil and Gas Show and Conference, 10-13 March, Manama, Bahrain, SPE-164258-MS (2013).

[3] Glénat, P., Anderson, R., Mozaffar, H., and Tohidi, B. “Application of a New Crystal Growth Inhibition Based KHI Evaluation Method to Commercial Formulation Assessment”, Proceedings of the 7th International Conference on Gas Hydrates, Edinburgh, Scotland, United Kingdom, July 17-21 (2011).

[4] Luna-Ortiz, E., Healey, M., Anderson, R., and Sørhaug, E. “Crystal Growth Inhibition Studies for the Qualification of a Kinetic Hydrate Inhibitor under Flowing and Shut-In Conditions”, Energy and Fuels, 28, 2902–2913 (2014).

[5] Mozaffar, H., Anderson, R. and Tohidi, B. “Reliable and Repeatable Evaluation of Kinetic Hydrate Inhibitors Using a Method Based on Crystal Growth Inhibition”, Energy & Fuels, 30, 10055−10063 (2016).

[6] Tohidi, F., Anderson, R. and Tohidi, B., “Effect of acid gases on kinetic hydrate inhibitors”, The Journal of Chemical Thermodynamics, 117, 119-127 (2018).

[7] Anderson, R., Tohidi, F., Mozaffar, H., and Tohidi, B. “Hydrate Inhibitor Removal from Produced Waters by Solvent Extraction”, Journal of Petroleum Science and Engineering, 145, 520–526 (2016).