The following is a case history where the client required a pigging solution for utilisation in a multi start/stop scenario, carrying a wax dissolver through a multibore pipeline.
The client requested that wax deposits, which had built up in the pipeline, be removed to improve flow assurance and pipeline operability.
The client required a wax dissolver to be transported down the pipeline. The line was 30 km in length, with an OD of 10 in. It was connected to two risers, one was 8 in. dia., and the second was 10 in. EVO-Pigs are considered to be particularly suited to this type of application because of their ability to reduce in diameter by up to 50%, helping ensure they do not get stuck in the line.
The project plan
In this operation, the pigs were to be utilised as separators to allow slugs of wax dissolver to be delivered to the affected areas, with the pig train being stopped every 500 m to allow the dissolver to soak into the wax deposits and dissolve them.
The pigs were driven by water. The activity sequence was as follows:
- 120% line volume water flush of system.
- 8 in. riser 24 hr soak. The EVO-Pig was launched prior to the dissolver, to prevent dissolver loss to main pipeline. The riser was then filled with 17 m3 of wax dissolver down to base at tie in spool.
- 10 in. riser 24 hr soak. The EVO-Pig was launched prior to the dissolver, to prevent dissolver loss to main pipeline. Then the riser filled with 30 m3 of wax dissolver down to base at tie in spool.
- Commence a pig run utilising two EVO-Pigs with a 4 m3 slug of wax dissolver.
- Commence a pig run utilising two foam pigs (supplied by other) with a 4 m3 slug of wax dissolver. Upon the launch of the second foam pig, the train became stuck in the riser and had to be removed through back flushing.
- Commence a pig run utilising two EVO-Pigs with a 20 m3 slug of wax dissolver. The train was stopped at 500 m intervals to allow the dissolver to soak into the wax deposits. This repeated for the first 3000 m of the pipeline.
- Final water flush carried out.
The EVO-Pigs successfully formed a pig train to carry the wax dissolver through the pipelines varying diameters and bends. The client was delighted to find an effective solution that allowed a pig train to be started and stopped to enable the dissolver to remove the unwanted wax deposits, improving flow assurance through the pipeline.
- Unlike foam pigs, EVO-Pig’s physical properties do not change under compression and can return to their original size.
- EVO-Pigs worked where the foam pigs got stuck, causing a risk of permanent blockage and potential loss of time and oil revenue.
- EVO-Pigs successfully transport liquids or gels when used in a pig train and can be stopped and started for soaking operations.