Ensuring Subsea Pipeline Availability in the Bonga Field
Authors: Oni David Wale , Bhat Shankar , Wemimo Oluwasegun , Unegbu Chukwudi , Ho Harry 
Published: April 2024

Subsea Pipelines systems are key to ensuring safe evacuation of liquids from the wells and reservoirs to the Floating Production StorageOTC-35118-MS and Offloading (FPSO). This paper acknowledges the direct relationship between top quartile asset integrity and pipeline availability hence presents the challenges and recovery path in operating and maintaining the Bonga Field subsea pipeline systems including first of its kind maintenance activities executed in the Bonga Field. This paper is one of a series of Bonga themed papers proposed for OTC (Offshore Technology Conference) 2024.

Routine inspection, surveillance and maintenance help drive improved availability. Lessons learnt through processes like after action reviews (AAR), risk-based inspection (RBI) and root cause failure analysis (RCFA) are documented and used to drive continuous improvement. For each asset integrity activity e.g. In-line inspection, riser, and flex-joint repairs, ROV (Remotely Operated Vehicle) scopes, Single Point Mooring Center Well Piping (SPM (Single Point Mooring) CWP) reinstatement, hydrate remediation, descaling intervention and boarding valve replacement, qualification of inspection method for flexible offloading risers, etc. These inspections, installations and bespoke repair procedures are developed with reference to international standards as applicable.

The Oil Export system, made up of the SPM and the Bonga oil offloading risers (BOORs) benefitted from in-situ replacement of corroded center well piping. In addition, the SPM hull was also refurbished using the cofferdam approach and these brought the SPM back into pristine state thus benefiting from a 20-year life extension. To further strengthen the oil export system, a tandem offloading system was proven, tested, and activated as a contingent export system in the unlikely event that the BOORS become unavailable.

The Gas export system was operated for 17 years without any challenge until a dehydration encounter from a glycol system upset led to a hydrate plug in the gas export pipeline. The plug was remediated, and barriers further strengthened to prevent reoccurrence. Also, the Gas Export Pipeline Flex Joint was replaced in a first of its kind in Deep Water Nigeria.

The water injection system experienced leaks from welds at the seafloor. RCFA conducted and bespoke clamps engineered to provide permanent repair and follow-on controls developed. The uniqueness of precision repair despite restricted access from cutting sled to gain access to repair site to precision clamp installation and lastly installation of retrofit beam for structural integrity was novel.

The pipe-in-pipe production flowline loops with bore restrictions and scale build-up de-scaled and intelligently pigged using advanced technology. Details of the trouble shooting, adopted solution and outcome of AAR is described in the full publication.

This article is an embodiment of Deepwater Pipeline Integrity management, life extension and asset integrity challenges and how these challenges were overcome, followed by additional controls to prevent future failures. It covers classic topical subject the industry can learn from to include ‘In-situ Deep Water SPM refurbishment,’ Hydrate Remediation, Difficult to Pig Deepwater Pipeline Bespoke Precision Deepwater Pipeline repair, FlexJoint in- replacement and 3D (Three Dimensional) Photogrammetry inspection.