Barium Sulphate Inhibition in Subsea Systems - The Impact of Cold Seabed Temperatures on the Performance of Generically Different Scale Inhibitor Species

Inorganic precipitates (scales) are one of the major flow assurance concerns in offshore oil and gas production, and lead to significant reductions in productivity and costly workovers if allowed to form uncontrolled. Scale prevention by the use of chemical inhibitors, applied either by continual injection or by squeeze treatment into the near wellbore formation, has generally been regarded as the most cost effective solution to the problem. The increased development of subsea satellite production brings with it a number of additional challenges to the chemical control of inorganic scale. The requirement to control scale at low seabed temperatures (4 - 5°C) over long residence times presents a particular challenge. This paper examines the performance of three generically different scale inhibitor species including a polyvinyl sulphonate (PVS), a phosphino polycarboxylate (PPCA) and a penta phosphonate (DETPMP) under typical North Sea Scaling conditions. The relative performance of the different inhibitor species against Barium Sulphate scale is compared at temperatures between 5°C and 95°C and up to 22 hours residence times. Results show that the performance of different inhibitors are significantly affected and to different degrees as a function of temperature, and that this is not simply related to changes in supersaturation against barium sulphate precipitation. The performance of the phosphonate species DETPMP is significantly reduced at lower temperatures and this is related to reduced adsorption at the barium sulphate surface. However the performance of the PVS is significantly improved, indicating that such species offer the potential for improved scale control at lower seabed temperatures. PPCA is only marginally affected by reduced temperatures in a manner more consistent with the increased supersaturation against barium sulphate.