Case History

Choke Skid Replacement


There was an aging subsea choke skid which was due to be replaced in Tunisia.

In order to install a replacement and associated pipeline spools, deoiling of lines and provision of an environmental barrier were essential. Once the installation was completed, the lines were then required to be dewatered. SANCCUS gel pig train played an important role in the successful accomplishment of this project.




The choke skid was connected to the topside through a 10" flowline. Diver Support Vessel (DSV) arrived at the operation site.


Step 1

Glycostat Gel was injected via a hot-stab with 3/8" bore on the tree at lowered viscosity. It was then pushed towards the topside by treated seawater, displacing hydrocarbons in the lines.


Step 2

After depressurising the system, the temporary pig launcher was installd by removing the 10" tie-in blind flange. It had 4 valved nozzles as per blue arrows and was pre-loaded with 3 M-Gel Pigs and MEG. Each gel pig was shaped in a way that would create gaps so they can be launched individually by functioning the valves.


Step 3

1st and 2nd pigs were launched and propelled by slugs of Glycostat Gel from DSV.


Step 4

3rd pig was driven by treated seawater.


Step 5

Once the gel pig train had reached the pre-determined location and deoiling operation was completed, the topside was opened to atmosphere and temporary launcher valves were opened. This allowed the pig train to flow back and the pressure in the system was equalised naturally.


Step 6

With the gel pig train forming an environmental barrier, the new 6" choke skid and its tie-in spools were installed. They were then flooded with treated and coloured seawater for leak testing.


Step 7

Nitrogen gas was injected from the topside, propelling the pig train towards the new choke skid to dewater the lines. Gel pigs extruded through the 10" - 6" transition.


Step 8

The system ready to be back online.


MEG based Glycostat Gels and M-Gel Pigs were successfully used for subsea pipeline flooding operations, displacing hydrocarbons to accomplish the installation of the new choke skid and associated pipeline spools. The same gel pig train was used to subsequently dewater the lines.


SANCCUS gel pig train effectively fulfilled 3 objectives in a single application - deoiling, environmental barrier and dewatering. It also enabled the treatment of the lines with multiple diameters.

The shape and viscosity of Gels and Gel Pigs can be tailored to each project. The project demonstrated the flexibility and versatility of Gel technology at its best.


We know from years of experience that no two jobs are identical. We will work closely with you to provide the appropriate gel and/or gel pig combined with reliable technical advice and support to give you the best possible outcome. Get in touch with us for a tailored information pack.


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