4 / 2021-07-31 18:56:56

Thermal conductivity of hydrate deposits formed in subsea deadlegs

Hydrate, Deposit, Insulation, Thermal Conductivity, Subsea, Deadleg

Gas hydrate deposition is one of the main reasons that could lead to the plugging of subsea oil and gas production flowlines. Similar to wax and frost deposits, hydrate deposits formed along the subsea pipe wall also effectively work as an insulating layer. In this work, in order to quantitatively investigate the thermal properties of hydrate deposits, a series of hydrate deposition experiments were conducted in a subsea deadleg setup for water-saturated gas-filled systems, where water condensed on the cold surface gradually converted to hydrate deposits. After the experiments, the thickness distribution of the hydrate deposits along the pipe wall was measured by borescope detection. The average porosity and average dryness of the hydrate deposits were also calculated. Based on the measured deposition thickness, the thermal conductivity of the hydrate deposits was calculated according to the heat balance between the natural convection on the surface of the deposit growth front and the heat transfer through the interior of the hydrate deposits. Then, based on the calculated hydrate deposit porosity, dryness and thermal conductivity, the thermal conductivity of the pure hydrates inside the hydrate deposits was determined. The effects of gas temperature and deposit thickness on the calculation results of the thermal conductivity were also investigated in this work. The conclusions in this work adds knowledge to the key properties for hydrate management in subsea deadlegs and flowlines.