Page 343 - Handbook Of Multiphase Flow Assurance

342 10. Research methods in flow assurance

Cooling system for the loop should be able to maintain a length of tubing chilled to a tem-
perature below the wax appearance temperature.
Wax loop may be equipped with removable or transparent pipe spools to observe wax
solids either as final deposit or during flowing or non-flowing conditions.

• Hydrate formation loop requires a gas compression/charge system to supply gas and
pressurize the loop before the test start and after hydrate formation consumes gas.
Pressure control system should maintain set pressure irrespective of temperature changes
or gas consumption into hydrates.
Either rotating vane or progressive cavity pump is required to circulate water with gas
hydrate particles. Hydrate solids can be broken up by the pump impeller. Low shear type
pumps are preferable for a hydrate loop in order to better evaluate the hydrate slurry flow.

• Multiphase flow loop requires a gas compressor in addition to a liquid pump, and a
separator to allow recirculation of the test fluids. Temperature control may not be as
important as for the paraffin and hydrate loops.

Flow loops allow to study formation of solid (wax or hydrate) or liquid (slug) obstructions
to flow. However, flow loops require costly maintenance and are only suited for universities
or research companies which work on joint industry projects.

Bench scale tests

A variety of bench scale laboratory tests may be done to research the growth of flow assur-
ance solids. The more common ones are listed below.

Paraffin cold fingers

A cold finger may be assembled with a relatively low cost. The main parts include a flask to
hold heated oil, a stirred heater, a magnetic stirrer, a steel tube, rubber hoses and a cold bath
with a water pump or a temperature-controlled circulating cooler. Oil in the flask should be
heated to just above the wax appearance temperature.
The cold bath with ice water may be used to approximate the deepwater temperature
which is close to 4 °C, or as low as −2 °C in Arctic subsea.
Cold finger will show how much wax deposits at different wall temperatures and with
different chemical additives.

Paraffin cross-polarized microscope CPM

A CPM may also be assembled at a relatively low cost. The main parts include a micro-
scope, a cooling stage made of quartz glass and two polarized lenses. The use of quartz glass
is important as it does not rotate the plane of light polarization. A temperature-controlled
cooler will be required for chilling oil sample to induce wax crystallization.
CPM will show how wax crystal form at different cooling rates and with different chemical
additives.