+1 vote

How is the volume of methanol injection required calculated for subsea injection?

asked Apr 12, 2014 in Process by Dan01 (1,560 points)
Same question for LDHI?

1 Answer

+1 vote
answered Apr 14, 2014 by karthikrg (1,090 points)
This is a loaded question in my opinion, and there are no straight answers. Depends on a lot of factors such as bubble point, water cut, undersaturation conditions etc. Some folks believe that if you prepare for 2-3 platform shut-ins per year, you would be covered, whereas some people think this is overdesign.

Somewhat of a simple answer is this:

If you are talking about shut-ins, and assuming that the water level following a shut-in and stabilization is above the SCSSV and potentially above the seabed, then this needs to be displaced below the SCSSV. Bullheading volumes for this case needs to be calculated.

If the shut-in is planned, (unlike the above), then MeOH can be injected continuously prior to shut-in so all the fluids are treated prior to the shut-in. Then the operator has the choice to inject MeOH during restarts until the system is outside the hydrate region.

During extended shut-ins, then the tree and wellhead jumpers, and manifolds need to be displaced with MeOH as well.

Put all this together, plan for a couple of unplanned events a year, and you have a conservative MeOH storage capacity.

LDHI is fairly similar, but bullheading should not be included (very expensive). LDHI treatment rates for continuous injection during a planned shut-in or a restart are of the order of 0.5-3.5% based on water rate.

Email me if you have a specific situation (karthik@gateinc.com).