Comparing the Kinetic Hydrate Inhibition Performance of Linear versus Branched Polymers.

Kinetic hydrate inhibitors (KHIs) are a chemical method of preventing gas hydrate plugging of oil and gas production flow lines. The main ingredient in a KHI formulation is one or more water-soluble amphiphilic polymers. Poly(N-vinyl caprolactam) (PVCap) is an unbranched polymer and a well-known industrial KHI, often used as a yardstick to compare the performance of new polymers. The effect of branching PVCap on KHI performance has been investigated by polymerizing the VCap monomer in the presence of varying amounts of trimethylolpropane triacrylate, pentaerythritol tetraacrylate, or bis-pentaerythritol hexaacrylate cross-linkers to give PVCap polymers with 3, 4, and 6 branches, respectively. If the ratio of cross-linker to VCap was too high (6:1 to 8:1), gelling and/or poor water solubility was observed, giving short polymer chains and poor KHI efficacy. For higher ratios (30:1 to 60:1), it was found that the concentration of the polymer needed to give total inhibition of structure II tetrahydrofuran hydrate crystal growth could be lowered by using tribranched rather than linear PVCap. Slow constant cooling (1 °C/h) gas hydrate experiments with a synthetic natural gas in steel rocking cells at 76 bar were also carried out. A small improvement in KHI performance was observed for one of the branched PVCaps compared with a linear PVCap. Branched and linear poly(N-isopropylmethacrylamide) (PNIPMAm) polymers were also investigated in the gas hydrate system, but there was no benefit observed when branching this polymer class.

Sustainable Calcite Scale Inhibitors via Oxidation of Lignosulfonates.

Deposition of inorganic scales in wells, flow lines, and equipment is a major problem in the water treatment, geothermal, or upstream oil and gas industries. Deployment of scale inhibitors has been adopted worldwide for oilfield scale prevention. Commercial synthetic scale inhibitors such as polymeric carboxylates and sulfonates or nonpolymeric phosphonates offer good scale inhibition performance but often suffer from one or more limitations including biodegradability, calcium compatibility, and thermal stability. Lignin-based biomaterials such as sodium lignosulfonates are natural, sustainable, and widely available polymers that are accepted for use in environmentally sensitive areas. Here we show that, although lignosulfonates perform relatively poorly as calcite scale inhibitors in dynamic tube blocking tests, oxidized lignosulfonates show a much improved inhibition effect by a factor of 20-fold. The oxidized lignosulfonates are easy to prepare in a 1-step reaction and show excellent calcium compatibility and thermal stability, useful for downhole squeeze treatments in high temperature wells. This present study unequivocally establishes oxidized lignosulfonates as a new class of sustainable green scale inhibitors, thereby bridging the gap between materials derived directly from nature and the classic synthetic polymeric scale inhibitors.