Reusable Wellhead Platform Jacket Conceptual Study
Authors: Uiyyasathian Sarayut , Anujareearpa Noppadol 
Published: February 2023

The objective of the study is to investigate feasible jacket and foundation design configurations, safe and reliable methodology and technics of transportation and installation of a new reusable wellhead platform jacket to serve phased development at the initial stage. The jacket is also designed to be able to retrieve, relocate and reuse at a new location for a future development. Development costs of utilizing of the newly built and reused wellhead platform jacket are determined.

Various concepts of engineering design and construction and relocation-ability screening were conducted, and a most suitable concept was selected. Preliminary foundation and jacket sizing based on existing soil data, site conditions, water depth and project requirements with considerations of construction and relocation-ability of both newly used and to be reused stages was verified.

Further detailed analysis to determine foundation and jacket sizes, overall structural integrity of the selected designs of both stages were further refined and confirmed. Further assessment of construction-ability and operation risks of both stages was conducted. Corresponding costs of both stages based on engineering designs and construction methodology were estimated.

It is found that the selected reusable concept for wellhead platform jacket is technically feasible. The suction pile foundation is proven and of ease of installing and retrieving. Due to heavy structural weight corresponding to the design water depth, from transportation and installation approach, the newly built structure is designed in two parts 1) base frame with suction caissons foundation 2) top part jacket. Both parts will be connected by grouting method.

When reuse, the entire structure will be retrieved, lifted above the seabed, wet towed and installed on to a new location in the field by a heavy lift vessel.

It is recommended that the following activities to be carried out in the next engineering phase:

Revisit all analysis when the actual soil data at the new determined location is available since it is the most critical input for engineering design and corresponding jacket weight that defines the heavy lift vessel requirement. Find opportunity of obtaining other alternative heavy lift vessels if they have reasonably competitive day rate or opportunity to combine the work with another project or campaign to optimize mobilization cost. Further analyses project schedule, competitiveness, possibility of multiple times of re-use the jacket and geo-politic risks into EPCI bidding campaign.

This implementation would be considered as PTTEP's first reusable offshore platform jacket design concept for such the water depth. Retrievable suction caisson base frame foundation, connecting jacket by grouting method at the initial stage and retrieving, wet towing entire structure altogether and installing on to the new location at a future stage is technically feasible. It could reduce CAPEX and improve economic of marginal field development project, maximize recoverable resources, reduce amount of waste that in line with PTTEP's Sustainable Development strategy.