Kinetic Hydrate Inhibition at Pressures up to 760 Bar in Deep Water Drilling Fluids

Kinetic hydrate inhibitors (KHIs) have been used successfully in the field for about the past 15 years to prevent gas hydrate formation mostly in gas- and oilfield production lines. They work by delaying the nucleation and often also the growth of gas hydrate crystals for periods of time dependent on the subcooling in the system and the absolute pressure. In this paper, we have investigated whether KHIs can be used at very high pressures, particularly for use in ultra-deep-water completion and water-based drilling fluids (WBMs) with high salinity. Compatibility tests were carried out on various brines with several commercial KHIs. Laboratory hydrate equilibrium experiments were conducted on WBMs up to 800 bar. K HI performance tests were carried out in a 500 mL stirred steel autoclave at pressures up to 760 bar. These are much higher pressures than have ever been previously reported for any KHI studies. With the previous knowledge that not only the subcooling but the absolute pressure (70-150 bar) affects the performance of KHIs, our results indicate that, even at the highest pressures investigated, KHIs can still give substantial delays in hydrate formation as long as the subcooling is not too severe and the brine salinity is high.