Multi-functional Flow Assurance Chemicals: Corrosion and Kinetic Hydrate Inhibition from Maleic Anhydride:N-Vinyl Caprolactam Copolymers and Synergists

Water-based flowassurance issues include corrosion,scale, andgas hydrate formation. Chemical solutions to mitigate these issuesusually require separate inhibitors, which sometimes can lead to compatibilitydifficulties. Herein, we report studies on maleic-based copolymersto combat hydrate and corrosion with a view to optimizing for scaleinhibition also. The product of maleic anhydride:N-vinyl caprolactam copolymer reacted with 3-dibutylaminopropylamine(MA:VCap-DBAPA) and its amine oxide derivative (MA:VCap-DBAPA-AO)were the kinetic hydrate inhibitor (KHI) polymers investigated. Dueto limited CO2 corrosion inhibition (CI) by the polymersalone, various oxygen-, sulfur-, and nitrogen-based additives werescreened for improved CO2 CI and possible KHI synergy.KHI performance screening tests were conducted under high pressurewith a structure II-forming natural gas mixture in steel rocking cellsusing the slow (1 degrees C/h) constant cooling method. CO2 corrosion inhibition was measured by linear polarization resistancein a stirred 1 L CO2 bubble test apparatus using C1018steel coupons and 3.6 wt % brine at 20.5 degrees C. Several sulfur-basedadditives improved the CI efficiency of the maleic polymers, especiallybutyl thioglycolate and 2-aminoethanethiol, without a negative effecton the KHI performance. For example, 2500 ppm MA:VCap-DBAPA plus 1000ppm butyl thioglycolate gave an average hydrate onset temperature(T (o)) of 4.4 degrees C (12.7 degrees C belowthe T (o) for no additive) and 99.7% CI efficiency.In contrast to a classic fatty acid imidazoline surfactant corrosioninhibitor, butyl thioglycolate was also found to greatly enhance theCI efficiency of industrial KHIs, poly(N-vinyl caprolactam)(PVCap) and N-vinyl pyrrolidone:N-vinyl caprolactam copolymer, with no antagonism to the KHI performanceof the polymer. In addition, butyl thioglycolate boosted the KHI performanceof PVCap. The use of small synergists such as butyl thioglycolateavoids the use of classical surfactant corrosion inhibitors whichcan lead to tighter emulsions and poor overboard oil-in-water quality.