Kinetic Hydrate Inhibition with N-Alkyl-N-vinylformamide Polymers: Comparison of Polymers to n-Propyl and Isopropyl Groups

Abstract

Gas hydrates in the upstream oil and gas industry often cause problems during production, such as plugged pipelines causing down time and loss of revenue. Kinetic hydrate inhibitors (KHIs) have successfully been used in the field for about 2 decades. KHIs work to delay hydrate nucleation and/or crystal growth in the hydrate-stable operating region. KHIs, such as polymers containing N-vinyl amide units, for example, methacrylamide-based KHI polymers with isopropyl groups, have been commercialized and are now used in field operations. However, there are no reports of polymers with n-propyl groups that have been commercialized as a KHI. Using a structure-II-forming natural gas, we have now investigated the KHI performance of homopolymers with n-propyl and isopropyl groups based on the N-vinylformamide (NVF) monomer. A range of copolymers with NVF with higher cloud points were also synthesized and tested because the cloud points of these homopolymers were found to be lower than preferred for most field operations. The polymer series containing nPr-NVF monomer was found to perform better as KHIs than the iPr-NVF series as KHIs at 2500 ppm concentration in deionized water at all copolymer ratios with a similar molecular weight. Two of the best polymers from each of the nPr-NVF and iPr-NVF series were tested at varying concentrations from 1500 to 5000 ppm. A similar trend was found as with the tests of the complete series, in which the nPr-NVF polymer performed better than the iPr-NVF polymer. Poly(N-(n-propyl)-N-vinylformamide) homopolymer gave a similar KHI performance as a commercial sample of polyvinylcaprolactam (PVCap).