ANNUAL TRANSACTIONS OF THE NORDIC RHEOLOGY SOCIETY, VOL. 14, 2006 High pressure hydrate detection in a stirred vessel R. B. Schüller, J. Funner, V. Mathiesen, I. Gjermundsen and H.K. Kvandal Hydro Oil & Energy Research Centre, 3900 Porsgrunn, Norway. ABSTRACT Measurements have been undertaken in a stirred vessel on pressurised saturated hydrocarbon/water mixtures from the North Sea. Hydrate formation and dissociation was detected, and the increase in mixing torque was quantified. Stirred vessels, fitted with suitable pressure and temperature control facilities, can be used to characterize many of the important parameters coupled to the presence of hydrates in production systems. The measurements have been undertaken on pressurised systems containing hydrocarbon liquid, mixed with saline water and saturated with hydrocarbon gas. The oil/water dispersions have then in turn been tested in a stirred vessel of volume 500 ml with pressure and temperature control. Typical test pressure has been 50 bars, and the temperature during hydrate formation typically 2 °C. INTRODUCTION Clathrate hydrates 1, 2 may form in oil production facilities when the pressure and temperature favour the growth of hydrate crystals. Typically, at a pressure of 50 bar hydrates may form when the temperature falls below approximately 20 °C. The presence of hydrate crystals in the fluid may cause a significant increase in viscosity. From a production point of view this poses a threat to both production capacity and possible blocking of the production pipeline if the hydrates form a plug. The strength of pure clathrate hydrates can be 20 times stronger than ice 3 , but this may not be comparable with the strength of solidified dispersions containing hydrate particles. The presence of hydrates in oil and gas transport systems poses a threat to the continuous production process. It is therefore of great importance to be able to characterize dispersions containing hydrates with respect to both flow properties and strength. The present work focuses on saturated oil/water system where the water volume fraction is less than 50%, thus forming a water in oil dispersion or a partially stratified system before hydrates are formed. Similar hydrate tests have also been made in rheometers 4 . The flow of hydrate dispersions in pipelines has been investigated by several authors 5, 6 . Hydrate growth is often inhibited by the addition of Methanol or Glycols affecting the thermodynamic equilibrium. Kinetic hydrate inhibitors, slowing down the rate of hydrate growth or delaying hydrate formation, have been investigated by several authors 2, 5 . Some oils also seem to contain components that act as natural inhibitors 7, 8 that prevent the formation of hydrates. Published information on the rheology of hydrate dispersions include characterization of hydrate suspensions 9 , investigations on the flow properties of hydrate in water