Gas hydrate formation in flow lines is of notorious concern for the oil and gas industry, and it only gets bigger because of the never-ending pursuit of oil and gas compels the industry into deeper and colder waters. Gas hydrate can form and agglomerate into plugs, jeopardizing hydrocarbon production. Therefore, a variety of methods have been developed to inhibit gas hydrate formation. One of these is to utilize chemicals in the form of low dosage hydrate inhibitors (LDHI), which consists of two categories, kinetic hydrate inhibitors (KHI) and anti-agglomerants (AA). KHIs, the focus of this thesis, are mixtures of one or more water-soluble polymers in solvents and synergists.
In order to find KHI chemicals with better inhibiting capabilities and/or environmental properties, the mechanism as to how KHIs operate must be better understood. The understanding of gas hydrate formation and the effect of different KHIs has been enriched by a large number of experimental studies using a plethora of research techniques, gaining insight into the gas hydrate nucleation and growth processes, coupled with the possible modes of action of KHIs. Investigations were carried out on both the macroscopic and microscopic scale. Despite all these endeavours, no clear consensus on the inhibition mechanism exists in the hydrate community, which limits the ability to design improved KHIs. Therefore, investigating new KHI polymers and synergists can help understand the structure-activity relationship and factors involved in the KHI mechanism.
This PhD study consists of two main agendas, 1) investigating different compounds for their potential capabilities as synergist with probably the most well-known industrial KHI polymer, poly(N-vinyl caprolactam) (PVCap) and 2) investigating novel alternatives for PVCap as KHIs which also contain pendant caprolactam rings. Several excellent new synergists were discovered and a new class of acrylamido-based caprolactam polymers were synthesized and developed to give good KHI performance. In addition, the stability of PVCap and related KHI polymers was studied at a wide range of conditions including temperature and pH. This is relevant for field applications at extreme conditions.
In another study, literature and experimental studies were used to determine if there is a correlation between polymer cloud point and KHI inhibition performance. The results showed that a low cloud point, near the hydrate formation temperature, was useful for high KHI performance of a polymer but only if certain criteria are met. These include low molecular weight, pendant hydrophobic groups of an optimal size close to the polymer backbone and the correct neighbouring hydrophilic functional groups. Finally, a new class of non-amide-based polymers, polyvinylaminals, were investigated as KHIs. For testing the inhibition capabilities, for both the synergist mixtures and the novel polymers, high-pressure rocking cells with synthetic natural gas mixture with either slow constant cooling or isothermal test regime were mainly used. These studies have resulted in nine journal publications
