Case History

Subsea Flexible Pipelines


There were extensive sections of flexible pipelines in an offshore oilfield that required to be replaced/reconfigured. Prior to the operation, these sections needed to be degassed, filled with either an environmental barrier or treated seawater. Once replaced/reconfigured, the lines then required to be leak tested and dewatered before being brought back into service.

Working closely with the client from the planning stage, SANCCUS came up with the solution which combines the use of Pipeline Gels and Gel Pigs to achieve the desired result efficiently.


Oilfield Overview


The pipelines are running across 3 rigs in the field and connected through Subsea Isolation Valves (SSIV). From left to right - Rig 1, Rig 2 and Rig 3. Rig 1 was expected to be decommissioned in near future.


Rig 1 & Rig 2

Part of the lines between Rig 1 and Rig 2 had a requirement for an environmental barrier as well as degassing.


Step 1

Treated seawater was pumped in from the Diver Support Vessel (DSV) through SSIV to Rig 1.


Step 2

Glycostat Gel was injected from DSV to push treated seawater further to degass and also to form a barrier.


Step 3

Functioning SSIV valves, Gel was injected from DSV up to Tee piece.


Step 4

DSV connected its downline to Tee and started pumping Gel towards Rig 2, degassing the lines as it's pushed by treated seawater.

Phase1 Complete

Step 5

The lines between Rig 1 and Rig 2 ready for subsequent operations.


Rig 2 & Rig 3

DSV moved on to the area between Rig 2 & Rig 3.


Step 6

DSV pumped in Glycostat Gel through SSIV to Rig 2, degassing as it's propelled by treated seawater.


Step 7

Repeat the same sequence on the line between SSIV and Rig 3.


Step 8

The line between Rig 2 and SSIV was disconnected and new line was installed to replace this section. The line from Rig 1 was blanked off with a flange.


Step 9

M-Gel Pig was introduced to SSIV by a diver.

Leak Test

Step 10

Triethylene Glycol was injected from DSV for the leak test.


Step 11

Propelled by nitrogen gas, M-Gel Pig was driven towards Rig 2, dewatering the line.


Step 12

The same method was employed to replace, test and dewater the line between SSIV and Rig 3. The lines between Rig 2 and Rig 3 ready to be back online.


Glycostat Gel ensured the effective degassing as well as the provision of environmental barrier for future operations. M-Gel Pig successfully negotiated through flexible lines which had corrugated internal surface without any problem.


Extensive lengths of flexible pipeline were effectively replaced/reconfigured without compromising diver safety and environmental responsibility.

The versatility of SANCCUS Gel enabled the fulfilment of three purposes - degassing, environmental barrier and dewatering. By simplifying the application, it helped save both time and cost.


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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