Use Of Anti-Agglomerates for Sour Gases, High Water Cuts And Its Performance Evaluation

Abstract

Gas hydrates can be easily formed during the transportation of oil and gas in pipelines under certain conditions. Water content, low temperatures and elevated pressure are required for the formation of gas hydrates. The industry uses a number of methods to prevent blockage by hydrates such as thermodynamic inhibitors, kinetic inhibitors and anti-agglomerates. Large volumes of thermodynamic inhibitors are required for prevention of hydrate formation which may result in environmental concerns. Natural gas in the U.S. may contain as much as 15 to 25% of hydrogen sulfide, while the figure could be as high as 30 percent in the rest of the world. Some kinetic hydrate inhibitors available today may not be effective in gas streams with hydrogen sulfide. The objective of this work was to develop a hydrate inhibitor for sour environments at high water cut. This paper also investigated the effect of different operating parameters such as concentration of the inhibitor, percent water cuts (25, 75 and 100), salinity (10,000 and 50,000 chloride brine) and gases (hydrogen sulfide, nitrogen, butane, carbon dioxide, propane ethane and methane). These anti-agglomerates were compared with kinetic inhibitors. Hydrate inhibitor testing was performed using an autoclave at 4 °C. Pressure, temperature and torque were recorded. In this paper, we presented the development and use of a family of anti-agglomerate compounds that effectively function in a sour environment at high water cut. Torque measurements were used to determine the effectiveness of inhibitors. It was found in some cases that the torque for treatment containing ≤ 3% of these anti-agglomerates in 1% H2S was low (< 3 Ncm) compared to a control (> 20 Ncm) indicating no deposition of hydrates. Increasing the percentage of H2S to 4 % did not diminish the performance of selected anti-agglomerates. The best performing anti-agglomerate was also effective in both 10,000 ppm and 50,000 ppm chloride ions brine. These hydrate inhibitors maintained their effectiveness even with > 24 hour shut-in. Field studies on the application of selected anti-agglomerate was presented.