Operators of subsea pipelines sometimes find advantages in performing subsea to subsea pigging operations. This type of pigging may be necessary in order to facilitate a specific field layout or concept. However, operational pigging and inspection pigging from subsea pig launchers to subsea pig receivers can create several design and operational challenges. These are identified and addressed in this paper.
Two main types of pigging operations are identified.
Subsea Automated Pig Launcher (SAPL). This is an operational pigging system designed for individual subsea launching of pigs, from a barrel/cassette containing several pigs, to a subsea receiver. The process is controlled from a remote control centre, typically a platform.
Subsea to subsea intelligent pigging operations for inspection of the pipeline.
The main challenges are:
How do we kick the pig into the production fluid?
Added difficulty with bypass pigs
Long term storage of pigs subsea (in production fluid)
What do we do with the debris?
The need for a pig tracking management system
The methods and the solutions that we have chosen to use in recent projects are described. The background information leading up to the decisions and choices taken will be discussed.
Special focus will be given to the importance of planning for any subsea operational and/or inspection pigging up front in the field layout and design phases, i.e. at the same time as the commissioning pigging is defined.
The need for a reliable and safe pig tracking management system will be addressed and our observations with respect to this issue will be included.
The specific advantages for the Subsea Automated Pig Launcher will be highlighted, a short list of these are:
Subsea launching (no platform required)
Remote launching (no vessel or ROV required)
Multiple-pig cassette (reduced number of trips by service vessel)
No round trip pigging required (improved production uptime, no need for dual pipelines)
Inspection pigging with the same unit
RFO operations possible with ROV support / control only
This paper will present practical and sound solutions of how to perform subsea to subsea operational and inspection pigging in a cost effective and safe manner.
It will also highlight and explain the importance of planning for any subsea operational and/or inspection pigging up front in the field layout and design phase. This is often not a high focus element and this can result in very costly modifications later in the field life.