In today's world of high operating costs and low oil prices new methods of construction are needed to ensure economic viability. One such way is to maximise the use of an existing infrastructure.
Marathon utilized surplus power generated on Brae A and Brae B to supply the requirements of East Brae using transfer by 33kV sub-sea cable. First oil was produced in December 1993.
This resulted in platform weight savings of ground 3000 tonnes, with cost savings in excess of £60 million.
East Brae is the third of a three platform development located in the UK sector of the North Sea and operated by Marathon Oil UK on behalf of the Brue Group, see Fig, 1. First oil was produced from the East Brae reservoir, on schedule, during December 1993.
In today 's world of high operating costs and low oil price, new methods of construction are required to ensure economic viability. One such way to reduce expenditure is to maximise the use of the existing infrastructure, thus reducing weight. capital expenditure and operating costs.
Marathon utilised that existing surplus power generated on the Brae A and Brae B platforms to supply the power requirements of East Brae. This took the form of a "ring-main" between the three platforms. sec Fig. 2(Available in full paper).
There are four dual fuelled turbine/generator units installed on Brae A, each rated at 20MW, giving a total capacity of SOMW, the load on this platform is now 33MW.
On Brae B there are three dual fuelled turbine/generator units installed, each rated at 24MW, giving a total capacity of 72MW, the load on the platform is 27MW.
This gives an installed field capacity of 152MW and a firm capacity of 128MW. (152 - 24), The final load on East Brae will eventually be in the order of 20MW.
The total field power requirements will therefore be 33+27+20 = 80MW, which can be achieved by operating any five of the seven generators. This is sufficient for HT motor starting and also avoids the need to loud shed upon failure of a single generator.
Before a start could be made on the project it was necessary to confirm the feasibility of the proposed scheme and in order to arrive at that stage it was essential to make a number of assumptions. One of these was in respect of the platform loadings at the time when East Brae would come into production (late 1993).
Other assumptions made, concerning the Electrical Engineering aspect, were that the existing switchgear was suitable to absorb the extra current loading and that the fault level ratings of the switchgear were capable of taking the added fault contribution when the three platforms were inter-connected.
Load flow diagrams were produced showing the envisaged current flows when the platforms were interconnected. From these diagrams it was confirmed that the main bus-bar ratings were acceptable. The only modification required was that the "droppers" to the new circuit breakers for the sub-sea cable, from the main bus-bar, would have to be increased from 1600 amps to 2000 amps, the bus-bar rating.