OS6C-1:TRANSPORT OF HYDRATE SLURRY AT HIGH WATER CUT.

A.M. MELCHUNA(1), A. CAMEIRAO(1*),A. OUABBAS(1), J.M. HERRI(1), P. GLÉNAT(2)
1. Gas Hydrate Dynamics Centre, Ecole Nationale Supérieure des Mines de Saint-Etienne, France, 2. TOTAL – CSTJF, France
  
    Oil transportation in pipelines at the end of field production life implies high quantities of water which represents the dominant phase. Oil becomes the dispersed phase, and the process of crystallization of gas hydrates needs to be studied again, and compared to the previous works performed on the opposite system where water is the dispersed phase.
   
    The laboratory is equipped with a flow loop called Archimede where the hydrate transport is monitored from a differential pressure drop measurement following the formation of hydrates at low temperature (1°C) and under pressure (80 bars). Along the years, the loop has been completed with an FBRM probe (Focused Beam Reflectance Measurements), and ATR (IR measurement) probe and a PVM probe (Particle Video Microscope). These probes allow measuring the crystals sizes and shapes and controlling the gas concentration in the oil. These parameters are key elements in order to build crystallization and transport models and to better understand and quantify the way of actions of additives
   
    We have performed a parametric study based on the water content (60% - 90%), and liquid flow rates ranging from laminar to intermediate regime (200L/h and 400L/h) in order to observe the crystallization from a Liquid Kerdane (C11 – C14), Liquid water and methane gas system. We have realized a set of blanks and compare them with a set of experiments in presence of a dispersant additive.
   
    During the experiments the differential pressure drop increases according to the operating conditions. For the blanks, when the amount of hydrates reaches a critical zone, flow is stopped by either impossibility to transport too viscous slurry or hydrates sticking to the flow loop walls. We observe the benefice of adding dispersant chemicals to stabilize flow and prevent instabilities. In our presentation, the different situations are documented with the results of two  parameters: Chord Length measurement via the FBRM and direct visual observation via the PVM. Tests results at low water cut and high water cut show clear differences in hydrate crystals shapes and sizes.