When Angola Drilling Company (ADC) approached UWG last year for help in developing Sonangol P&P's Morsa West field, the company already had a concept in mind - a rig assembled conductor platform (RACP).
The objective was to turn this unusual concept into a reality in the shortest time and for the lowest cost possible.
Alan MacKenzie, who led the work at UWG, explains the challenges presented by the project. “Using the well conductors to support a simple wellhead platform is an elegant way of limiting the costs of oilfield development in shallower water, especially if, as was the aim in this case, you can install the entire structure from a drilling rig and without any special heavy-lift vessels.
“The engineering, however, is not so straightforward. As well as taking into account the usual stresses experienced by the conductors, you have to consider the weight loading that they have to withstand. In fact, the nature of the platform demands you combine the normal conductor riser analysis with the structural engineering elements of the design.”
The Morsa West RACP has four 30-inch OD conductors set in 17 m of water, supporting a deck weighing 65 t. A team of UWG engineers based in Norwich carried out the detailed design work, which was subjected to independent verification, in the space of just three months. Fabrication of the drilling template and the topsides at a yard in Cape Town, South Africa, was completed by August of 2005, and then all attention turned to Angola and the work offshore.
MacKenzie takes up the story. “First of all, we lifted the topside and subsea structures from a supply vessel and temporarily suspended them beneath the cantilevers of the self-elevating drilling rig, the TODCO 185 – we had specially modified the rig for this operation by the addition of suitable suspension beams. The conductors and 20-inch casings were then batch drilled, the subsea template being run to the seabed after the first of the four conductors had been installed. Once the conductors were in, we cut their tops to exactly the same elevation and then keel-hauled the topsides from its temporary suspension position and landed it on top of the conductors. Finally, we used a clamping mechanism to secure the topsides to the conductors. ADC later added a fifth well to the platform, drilled via an extra 30-inch conductor. I am pleased to say that the offshore operations, which called for considerable ingenuity at times, were completed without a single safety incident.
“A project like this is always going to lose out in the competition for headlines with the various high-profile, deepwater developments currently being pursued in the region,” MacKenzie says. “But it was certainly a highlight for the UWG team. This is the first such platform to be installed offshore Angola. It involved us in a particularly interesting riser analysis and tested our knowledge and experience throughout. We are all very proud of delivering this rather unusual platform for ADC and Sonangol efficiently and safely.”