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Laboratory evaluation of chemical and biological kinetic gas hydrate inhibitors

University of British Columbia

For practical purposes, kinetic hydrate inhibitors must perform in a predictable manner in the field. However, the complexity of the petroleum fluid composition, the presence of dissolved electrolytes, and high driving force (overpressure or sub-cooling), make it difficult to impossible task to achieve. In this thesis, the performance of two chemical kinetic inhibitors, polyvinylcaprolactam (PVCap) and polyvinylpyrrolidone (PVP), and two biological ones, type I and III antifreeze proteins (AFP I and III) were evaluated under conditions mimicking oil and gas filed ones. The evaluation was done by using a double high pressure stirred vessel (crystallizer), a high-pressure cell in conjunction with a rotational rheometer and a high pressure micro differential scanning calorimeter. Although the above noted inhibitors were found to prolong the hydrate induction time and reduce the initial hydrate growth in saline solutions, the rate was found to increase when hydrate crystals started to form in the gas phase of the crystallizer. Circular dichroism experiments suggested that the saline solution does not perturb the structure of AFP I and III. However, in the presence of NaCl, the inhibitory activity of AFP I to prolong induction time decreased while AFP III was more active. Here, increase in induction time was ordered: no inhibitor<AFP I<AFP III<PVCap<PVP. Moreover, in the presence of the PVP and PVCap increase in hydrate slurry viscosity was more readily. Once hydrate formed, decomposition started sooner and was slower. The addition of n-heptane created a 4th phase in the gas hydrate formation system under study. This resulted in an increase in the induction time and a slowing of hydrate growth. Unexpectedly, addition of PVP, PVCap and AFP I decreased induction time, whereas AFP III had no impact on hydrate crystal nucleation. Here, the inhibitors activity to delay nucleation was ordered: AFP I<PVP<PVCap<AFP III~ no inhibitor. Nonetheless, for all inhibitors, gas hydrate growth was significantly inhibited and no acceleration in hydrate growth was observed. Meanwhile, hydrate particles remained dispersed efficiently by addition of chemical inhibitors. Once hydrate formed, however, hydrate decomposition started later in the presence of AFPs and sooner in the presence of chemical inhibitors and took longer.

Text

2014-12-15

Attribution-NonCommercial-NoDerivs 2.5 Canada

http://hdl.handle.net/2429/51514

Chemical and Biological Engineering

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/2.5/ca/