Page 53 - Well Control for Completions and Interventions

44 Well Control for Completions and Interventions

Figure 1.19 Inhibition effectiveness of methanol and glycol.

Some wells, subsea wells in particular, have chemical injection lines at
the tree and/or downhole, specifically intended for methanol injection.
Similarly, during well testing operations methanol is normally injected
into the produced fluids upstream of the choke. This is particularly
important immediately after start-up, when temperature is likely to be
low and water-based fluid is being produced back to clean up the well.

1.1.9.3 Hydrate removal
Hydrate removal is normally accomplished by three methods. Lowering
pressure, raising temperature, or chemical dispersal.

1.1.9.3.1 Chemical disassociation
If a hydrate forms in the well, the biggest problem is often finding a way
to get chemical inhibitor to the hydrate. Methanol, although an excellent
inhibitor, has a relatively low density at 0.79 SG (6.58 ppg). If pumped in
at the surface, it is unlikely to reach the hydrate unless the liquids in the
well are of a significantly lower density. Glycol, 1.113 SG (9.3 ppg), might
be more successful in reaching the hydrate, but will take longer to work.
It can take a long time to remove hydrates by pumping inhibitors from
the surface, as the contact area is small (cross-sectional area of the tubing)
and a hydrate can be large.