Anti-Agglomerants Performance in Hydrates Management: Fundamental Insights

Gas hydrates represent both a possible energy source in the form of methane gas, and could provide a strategy for long-term CO2 repository. Gas hydrates are also a nuisance during the transport of oil and gas via pipelines, where their formation can block and sometimes break the pipeline, causing large environmental damages. The industry, including BP and E-ON, invests ~$500 million per year injecting methanol in pipelines. Unfortunately, methanol, to be effective, needs to be present in amounts exceeding 20% by weight, sometimes up to 50% of the transported fluid.

As the productive oil wells become more and more removed from onshore refining facilities, and as productive oil wells age, leading to increased amount of water produced, new strategies are desperately needed. The present project focuses on alternative chemicals that should be effective (1) at low weight fraction to reduce the amount of fluids transported and pumped through the pipelines; (2) at low temperature and for long time, to be effective through the entire length of the pipelines needed to reach the wells far from shore; and (3) in systems that contain large amounts of water, to allow the exploitation of ageing wells, which produce large amounts of water together with oil and gas.

These chemicals, considered in this project, are known as anti agglomerants (AAs), and they can be effective at concentrations as low as 5% by volume. BASF, Schlumberger, Shell, Champion and Halliburton manufacture and formulate anti-agglomerants. Although it is believed that AAs allow small hydrate particles to form, and then prevent their agglomeration into large plugs, their mechanism of action is not well understood. Consequently, their discovery is based on lengthy trial-and-error protocols conducted on systems representative of the fluids extracted from given oil and gas wells.

To enable the systematic discovery of new effective AAs, the fundamental research proposed here focuses on their molecular mechanism of action. Molecular modelling and massive computer simulations will be implemented, in synergism with detailed micro- and macro-scopic experiments, for a specific class of anti-agglomerants. These compounds contain three hydrophobic tails, and one extended hydrate-philic head that comprises both carboxylic and quaternary ammonium ions. These molecules have been chosen because macroscopic experimental observations show that by changing the length of one of the hydrophobic tails by just 2-6 carbon atoms, while maintaining the rest of the molecule intact, changes their performance from excellent to poor. Our hypothesis is that the molecular structure of a film of AAs formed on a hydrate particle affects the growth mechanism. Two possible mechanisms have been identified by preliminary simulations: (1) aggregation of hydrates, and (2) penetration of water through the AAs film. It is possible that one of the two mechanisms acts as the dominant one at different experimental conditions (e.g., varying salt concentration). The proposed research is designed to first understand and quantify the molecular mechanisms of action of the AAs under various experimental conditions, and then to understand which AAs molecular features can be tuned to maximise their performance.

The fundamental results expected are relevant not only for better understanding hydrates management, but also for better understanding the molecular mechanisms involved in all crystallisation processes. Such processes occur in a number of industries (e.g., pharmaceuticals, specialty chemicals, coatings, foodstuff) that represent the backbone of UK high tech manufacturing. The sectors that will be positively impacted by the proposed research include energy, manufacturing, chemicals and environment.

While the main impact expected from the proposed research is on the management of hydrates formation in flow assurance problems, industrial sectors that will benefit from the successful completion of the proposed activities include energy, manufacturing the future, chemicals and environmental.

As the proposed research will lead to understanding the mechanisms responsible for the performance of anti-agglomerants, it is likely that guiding principles will be provided for the synthesis of specialty chemicals that could be used as anti-agglomerants. The main beneficiary for these discoveries will be the service industry to the oil and gas industry (e.g., Schlumberger, Halliburton and Innospec). The oil and gas industry will benefit indirectly (e.g., BP, E-ON, Shell, Statoil, Tullow Oil, etc.), as it will be able to produce hydrocarbons from existing wells that are being depleted (as oil wells age, they produce larger amounts of water, which increases the likelihood of formation of hydrates in the pipelines). NOV Flexibles, a company that produces flexible pipelines for the oil and gas industry, will also benefit from the results of this research, as it will be less likely for the hydrates to form and disrupt the pipelines. The chemical process industry (e.g., Process System Enterprise, Ltd) will benefit from a better understanding of the physical processes involved with the formation of hydrates in pipelines. The specialty chemicals industry (BASF) will also benefit because new compounds are likely to be designed based on the proposed research. These chemicals could be manufactured by chemical companies operating in the UK (e.g., Unilever).
Other industries could also benefit from a better understanding of the fundamental mechanisms involved in the growth of crystals form complex systems. These include pharmaceutical companies, as they are interested in both formulating and delivering drugs, specialty chemicals, interested in the synthesis of new materials, coatings and even food industries.

The broad public will benefit from the proposed research from many points of view: it is possible that the proposed research will contribute to lowering the cost of producing fossil fuels from the North Sea, leading to reduced energy prices in the UK, it is possible that new chemicals will be designed using insights from the proposed research, which could lead to new jobs within the UK manufacturing industry, and preventing the formation of hydrates in oil and gas pipelines will reduce the environmental impact of fossil fuels, with benefits for the population at large.

The project will also contribute the development of skilled workforce in the UK, as one PDRA will be directly supported by this project, one post-graduate student is already being trained, possibly another post-graduate student will be trained in the research areas discussed herein, and several MSc/MEng students will be involved in the proposed research.