Location: Angola

Platform Design: Stacked Template Structure/Conductor Supported Platform

Key Features:

• 62m water depth
• 8 slots, 12 wells for production (single and dual completions)
• 42” Conductors have dual functionality of providing structural support
  of the platform and 36” well conductors
• 8m x 8m well configuration
• Fully installed by jack-up rig

Background

Our client required the development of new assets to create further production for Angola, with a primary objective to improve skill sets within local communities under the mantra “Built in Angola, by Angolans, for Angola”. This would create a new factory model for their future project delivery.

Fabrication and assembly were to be conducted in Cabinda, using facilities which hadn’t produced platforms since the initial development of its field assets dating back to 1970s. The existing field blocks had untapped reserves, and the challenge was to bring new production online in a timely and cost-effective manner, using local fabrication facilities and resources.

A Stacked Template Structure design (STS) was considered for inland fabrication in small module packages to allow road transport by trucks to the new construction site for final assembly, and loadout at the newly built quayside. The loadout facilities we only available to accommodate up to 500Te modules. Mobile cranes were to be used for each modular loadout onto PSV’s, due to quayside water depth restrictions.

Cost and time were key project drivers, along with developing local resources to support and create the infrastructure for future STS factory model platform production. Previous concept designs had been challenged by Aquaterra Energy to reduce the equipment requirements ensuring only functional operation equipment was required. Previous iterations of concept design had indicated a 1500Te + topsides weight due to electrical equipment was needed to exploit the reservoirs.

Limiting the complexity of the offshore facility was a key project driver, to ensure the full installation works could be completed with the use of a jack-up rig only removing the requirement for mobilising a heavy lift vessel.

Solution

Throughout the detailed design, Aquaterra Energy worked closely with suppliers, the client and the Angolan fabricator to design the STS structure into modular units for fabrication in the existing facilities. This also allowed them to be transported by road using trucks to the assembly area for final erecting to build the STS platform modules.

The STS factory model was the first of its kind to be constructed in Angola since the 1970’s. There were several challenges during the design phase that required careful consideration for a diverless installation. Each structural item was designed be erected under water with the use of a jack-up and an ROV.

Aquaterra Energy engineered a solution for the 62m water depth consisting of a mudmat and Lower/Upper Subsea Structure that was supported using a drilling deck module for early production (if required), plus a topside containing all the electrical and production facilities.

The substructure design was the third configuration successfully used to reduce cost, complexity, and time to first oil. The STS was designed not to exceed the weight limit and to ensure that all structural items had the ability to be lifted from the offshore support vessels using the jack-up rig within its operational capabilities.

Production utilises integrated ESP and associated ASD equipment on the 24 x 12m topside which is managed from a remote location.

Results

The platform was designed both in the UK and Angola, with all construction completed in Cabinda and delivered to the quay side – increasing the local content skill set. We supported with training operations teams and driving long term engagement with the local operations team.

The project was successfully fabricated, and installation completed during the Covid-19 pandemic.

ESG stats:

• 100% fabricated in-country
• Approx. 30% less steel required for Stacked Template Structure (STS), compared with a
  standard conventional jacket
• Generated over 1m local content hours of employment
• Zero LTIs
• Utilising existing in-country infrastructure for installation created savings on transport emissions
• Knowledge transfer and in-house training of platform and usability which supported enhanced skill set of local workforces