Synthesis, Performance And Application Of Kinetic Hydrate Inhibitors

The pipeline and gathering production equipment can be blocked by hydrates, which aredetrimental to the natural gas and oil exploitation, gathering and processing, resulting in hugeeconomic losses. Kinetic hydrate inhibitors (KHIs) are more favorably utilized to inhibit theformation of hydrates than thermodynamic inhibitors (TIs). From the mid-1990s, KHIs withfive ring or seven ring functional groups have been utilized in oil and gas industry more andmore widely. However, the impact and mechanisim of KHIs' ring members on hydrateinhibition is still not clear, and KHIs with good biodegradability and inhibition performance isin urgent need in oil and gas industry.In this study, new varieties of KHIs with different ring functional groups were designedand synthesized, and their performance in THF solution and water/gas/oil system to inhibithydrate formation was investigated. The biodegradability of KHIs in water was studied, andthe interaction between the hydrate particles with KHIs in n-decane was investigated. On thebasis of this study, one industrial product of KHIs was applied in gas field domestically.Three series of hydrate kinetic inhibitors were synthesized, namely PVP combinedinhibitors (HY), poly(N-vinyl2-pyrrolidone-co-4/2-vinyl pyridine)(HG) and poly(vinylcaprolactam-co-2-vinyl pyridine)(HN).The induction time of three series of hydrate kinetic inhibitors were tested in THFsolution. It was found that HY4inhibited THF hydrate formation more than18h with thesynergist of diethylene glycol monoethyl ether. The introduction of2-vinyl pyridine inN-vinyl pyrrolidone polymer can improve the polymer's THF hydrate inhibition ability, andTBAB can improve HG' inhibition ability in the aspects of enlarging subcooling andprolonging inhibitory time. HN's performance was superior to Inhibex501, and HN119couldinhibit THF hydrate formation for15.7h at-1oC. The adhesion forces of tetrahydrofuran(THF) hydrate particles in n-decane in the presence of some KHIs were measured. With PVPand Inhibex501, the contact surface of hydrate particles had larger viscous liquid bridgewhich promoted the adhesion force. While PVCap, HN13and HG15caused THF hydrateparticle surface roughness, thus contributing to lower adhesion force.The three series of KHIs and THF/PEO group-contained polymers' inhibitionperformance on natural gas hydrate was carried out. The mesuring system was heptane/water/gas at a subcooling of about10~12°C, and the amount of inhibitor tested was0.1wt%according to the water quality. It was found that the polymer containing five ring functional groups, PTHFMA-co-PEO inhibited natural gas formation for3.4h, and the inhibition time ofHY4was2.4h. With the amount of six functional groups increasing in the polymers of HG,their inhibitory performance was improved, and HG13and HG15could inhibit hydrateformation more than4h. As for the performance of seven and six ring functional groups ofHN, HN13and HN19's inhibition time were more than4h, while HN119's inhibition timecould be up to5.6h. PEO-co-VCap with seven ring functional groups can inhibit gas hydratefor3.5h. Based on the above results, it was proposed that in the gas dissolution and hydratenucleation stage, the performance of KHIs was determined by their hydrophobic andhydrophilic properties, the types of functional groups and ring members; on the hydratecrystal growth stage, the performance of KHIs was depended on their adsorption capacityonto the hydrate crystal, the polymer molecular size and polymer conformation in solution.The performance order of functional groups in polmers was seven ring> six ring> five ring.The biodegradability of KHIs was studied through their COD and BOD in aqueoussolution. HG's biodegradability were at about0.7, compared with HY4having a increaseabout10%, and HG17's biodegradability was prominently0.79; HN's biodegradability wasat about0.3~0.5. It was shown that the biodegradability of KHIs was determined by theirfunctional groups. The introduction of2-vinyl pyridine can improve the biodegradability ofKHIs.To evaluate the actual operational performance of KHIs, HY4was applied in anonshore gas field. HY4had a good hydrate inhibition effect on low condensate content naturalgas, and can prevent effectively gas hydrate pipeline blockage in the test period of10days.The methanol dosage can be reduced by over70%with HY4. HY4's application cost wasclose to methanol, but the sewage treatment was avoided.