Current Situation

The North Sea is a mature basin where production is decreasing and unit costs of production are increasing, the main trends causing this are:

Major fields currently in production are at a mature age where they are beyond their production plateau. These fields will reach a time when the production rate will fall to the point where it will no longer be economical to continue production using the in-place structures and current technology. This has already occurred on a number of fields, with the result that they have been shut down and abandoned.
The discovery of very large offshore oilfields, which justify huge upfront investment costs, is declining. New discoveries are increasingly small fields which are frequently isolated from existing infrastructures. The risks associated with the development of these so-called marginal fields are too high, under the prevailing technical and economic conditions, to justify the use of existing high cost solutions.

As a consequence of these factors, the development of a low cost production method would allow further field production to be economic at the lower production rates and short life cycles associated with depleting fields, and facilitate the exploitation of the growing number of marginal fields.

The Oil Production Buoy

For such marginal and end-of-life fields – with an expected production rate of up to 20,000 bbl/d and maximum recoverable reserves of the order of 20MM bbl – the high cost conventional solutions (FPSO, offshore platforms with subsea production systems etc) offer no economic solution for their development or continued production.

The concept of the production buoy is that it offers an alternative to conventional subsea tie-back development and reliance on a host facility. The buoy can provide:

Independence via subsea oil storage and tanker export.
Further utilisation of existing infrastructure by improving flow assurance.
Standalone control and utilities.

For the example of a production buoy applied to a marginal field, a brief description of a possible process is as follows:

Wellfluids are received from one or more wells.
Chemical injection and artificial lift via ESP or gas lift may be provided if required.
The oil is processed via a two stage separation and is thermally stabalised to meet the tanker export criteria of 10psi RVP and a BS&W of 2%.
Oil is pumped to the gravity base storage facility.
Associated gas is utilised to produce heat and electrical energy, using gas fired heaters, gas engines or gas turbines depending on the application.
Depending on the application, any gas not utilised for energy may be exported, flared or reinjected.
Produced water is either reinjected or passed through a de-oiling system for disposal to sea.

The buoy offers considerable cost savings (both CAPEX and OPEX) when compared to conventional offshore technologies due to:

The employment of a standardised base design to reduce design costs.
The use of smaller and lighter components than traditional structures.
A reduction in commissioning costs due to the lightweight and flexible nature of the buoy.
A reduced maintenance regime due to process equipment being protected from the elements by the buoy structure.
The utilisation of produced gas as an energy source.
Reduced personnel transport costs due to the longer maintenance intervals.
The facility to relocate the buoy rapidly at the end of a field’s life to another marginal or brown field site (the buoy can be fully operational as little as 72 hours after arrival).