Offshore production in ultra deep water may present several technical challenges. New exploration frontiers, sometimes, could provide a very complex scenario for oil production, considering very far fields from the shore, very harsh environmental conditions and the necessity of well intervention, to maximize the recovering factor of the field. Scenarios like that demands functional requirements for production units which can be very hard to achieve considering conventional Production Units.
The MPSO (Monocolumn Production Storage and Offloading) Unit concept has been being developed in recent years to combine small motion requirements and high stability with or without oil storage capability, with good results for oil production scenarios. However, the use of this type of Unit as a drilling Unit or for a dry tree completion scenario becomes a challenge in harsh environmental conditions, due to the very strict constrains required regarding motions and offsets of the unit.
In order to obtain a Monocolumn design with dry completion capability, considering the Brazilian shore pre-salt scenario, an optimization process was set up, evaluating thousands of different configurations considering motion and stability requirements. Mooring analyses were also performed to guarantee a small offset and a small set-down of the unit. As a result, a different platform design was obtained, with very small motions and dry completion capability.
For some scenarios considering pre-salt reservoirs, which are located in Santos Basin, in deep water productions fields, the use of dry completion Units could bring some economical advantages, as saving in rigging costs and rigging maintenance, a greater recovering factor of the oil fields and an improved capability of workover of the production wells. In 2008, Petrobras has performed assessments of different types of dry tree unit production platforms, as SPAR and TLP platforms. Besides that, a Monocolumn dry tree production platform concept was already designed for operations in those scenarios.
The Monocolun concept has been being developed for different companies, including Petrobras, which has your own concept, called MonoBR (Masetti et al, 2006), developed in partnership with the São Paulo University, as shown in Figure 1. Besides the Petrobras concept, there are alternative concepts developed by other companies as well (Syvertsen et al, 2004), (Orr et al, 2009). The main idea of the MonoBR was originally designed to be riser friendly considering Steel Catenary Riser subsea systems an the concept combines low motion levels with storage capability and great stability, which are concurrent requirements, in general. To achieve this objective, in general, it is necessary a huge Unit, deep draft and the Use of huge appendages to create vortex damping and added mass effects.