Sludge composition in Slug Catchers

[scanguy]

I have been asked if our company can determine a sludge level in a Slug Catcher. This is a new area for us and we wish to make a better informed descision. The enquiring contact has little info on the subject.

What I need to know is... What is the typical composition of sludge found in the base of the slug catcher? I have heard of pyrophoric metals, oils & tars and sand. Is this accurate and what makes up the bulk of the sludge. I believe the base is also liquid full as it is a separator, However, I am not sure as to what the liquid is. Is it water, oil, combination of both or something entirely different.

I appreciate your time and patience.
Thanks
Ian

 

[zdas04]

Ian,
There are few things more individual than the composition of any sludge. Every gathering system, pipeline, well, etc. will contribute a different mix of junk to sludge build up. Frac-sand is common. Coal is common in CBM. Iron Sulphide is common where where H2S is a problem (and it is pyrophoric). Various oxides of iron will be seen. Just plain dirt is often there.

In a finger-type slug catcher you will see different sludges in each finger. In a gathering system with multiple off-take points you'll see different sludges in the slug catcher at each off-take site.

Taking samples through a lubricator with the slug catcher in service is seldom effective because each strata in the sludge deposition can be completely different from the other strata.

Determining a sludge level is sometimes possible with an ultrasonic thickness meter and a very competent operator. The differences are quite subtle and easy to miss/mis-intrept. A video camera with a fiber-optic lens can be helpful, but the depth-of-field tends to be so short that it is quite an art to estimate sludge level from the pictures.

If they're asking for a hard-dollar bid, I'd add a LOT of contingency.

David Simpson, PE
MuleShoe Engineering

http://www.muleshoe-eng.com