Abstract
Kinetic hydrate inhibitors (KHIs) have been used for over 25 years to prevent gas hydrate formation in oil and gas production flow lines. The main component in KHI formulations is a water-soluble polymer with many amphiphilic groups, usually made up of amide groups and adjacent hydrophobic groups with 3–6 carbon atoms. KHI polymers are one of the most expensive oilfield production chemicals. Therefore, methods to make cheaper but effective KHIs could improve the range of applications. Continuing earlier work from our group with maleic-based polymers, here, we explore maleic acid/alkyl acrylate copolymers as potential low-cost KHIs. Performance experiments were conducted under high pressure with a structure II-forming natural gas mixture in steel rocking cells using the slow (1 °C/h) constant cooling test method. Under typical pipeline conditions of pH (4–6), the performance of the maleic acid/alkyl acrylate copolymers (alkyl = iso-propyl, iso-butyl, n-butyl, tetrahydrofurfuryl, and cyclohexyl) was poor. However, good performance was observed at very high pH (13–14) due to the thermodynamic effect from added salts in the aqueous phase and the removal of CO2 from the gas phase. A methyl maleamide/n-butyl acrylate copolymer gave very poor performance, giving evidence that direct bonding of the hydrophilic amide and C4 hydrophobic groups is needed for good KHI performance. Reaction of the maleic anhydride (MA) units in MA/alkyl acrylate 1:1 copolymers with dibutylaminopropylamine or dibutylaminoethanol gave polymers with good KHI performance, with MA/tetrahydrofurfuryl methacrylate being the best. Oxidation of the pendant dibutylamino groups to amine oxide groups improved the performance further, better than poly(N-vinyl caprolactam).
Highlights
Kinetic hydrate inhibitors (KHIs) have been used since the mid 1990s to prevent gas hydrate blockages in oil and gas production flow lines.[1−6] The potential formation of these icelike solids of clathrate small hydrocarbons constitutes one of the most significant flow assurance issues for offshore fields.[7−10] KHIs are formulations of one or more structurally specific water-soluble polymers in solvents and other synergists
The optimal KHI polymer will vary somewhat depending on the field conditions, but based on the jump in performance from our screening tests, it is likely that VA:maleic anhydride (MA)-60%cHex-40%DBAPA will be a significant improvement in maleic polymers for a range of field conditions
For the amination of maleic polymers, we used either water or nBGE as a well-known KHI high-flash point solvent synergist. nBGE was used in the original work on maleic-based KHI polymers in the 1990s
Summary
Kinetic hydrate inhibitors (KHIs) have been used since the mid 1990s to prevent gas hydrate blockages in oil and gas production flow lines.[1−6] The potential formation of these icelike solids of clathrate small hydrocarbons constitutes one of the most significant flow assurance issues for offshore fields.[7−10] KHIs are formulations of one or more structurally specific water-soluble polymers in solvents and other synergists. The optimal KHI polymer will vary somewhat depending on the field conditions, but based on the jump in performance from our screening tests, it is likely that VA:MA-60%cHex-40%DBAPA will be a significant improvement in maleic polymers for a range of field conditions This copolymer demonstrated excellent compatibility at high temperatures, giving no cloud point in water at 95 °C as a 1.0 wt % solution. Performance testing as KHIs of all polymers was carried out in high-pressure rock cells, which are rocked in a water bath at variable temperatures.[26,27] The rig (RC5) was supplied by PSL Systemtechnik, Germany. Standard deviations for all data sets were determined, assuming a normal distribution
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
