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The FPSO Kwame Nkrumah
The FPSO Kwame Nkrumah

Jubilee partners find solution to defective turret on FPSO Kwame Nkrumah

Partners in the Jubilee Field, the country’s first independently developed oilfield, have finally found a lasting solution to the defective turret of the FPSO Kwame Nkrumah after extensive technical investigations.

They have decided to employ a technique known as the Spread Mooring System as the best option, compared to hauling the FPSO back to the shipyard in Singapore or the nearest port that has the facility to receive the giant ship for maintenance.

According to the technical team that reviewed the options, the use of the spread mooring system was an excellent choice towards establishing the best long-term solution to the problem.

The FPSO Kwame Nkrumah was hitherto moored using the turret bearing system which allowed the production platform to rotate throughout its lifespan, depending on the weather conditions.

However, in February this year, the operators realised that there was a problem with the rotation of the turret which affected the production schedule, leading to a drop in output and export of gas to shore.

Approval, cost and duration

Currently, the partners are seeking approval for commencement of the first phase of the new mooring option, which will involve the installation of a stern anchoring system to replace the three heading control tugs currently at Jubilee.

The partners will then move into planning the second phase of work to remove the load of the turret and risers from the bearing to allow the FPSO to be on optimal spread moor in the first half of 2017.

Those phases of work, according to the partners, are expected to cost between $100m and $150m and it is estimated that the FPSO would have to be shut down between eight and 12 weeks in the first half of next year.

On completion of the spread mooring programme, production is expected to return to the levels achieved before the defect occurred.

The partners will review potential opportunities to improve the efficiency of off-take procedures and this may include the use of a larger dynamically positioned (DP) shuttle tanker.

FPSO challenges

The country’s premier oilfield production came with some level of challenges, resulting in one encounter after another since first oil was produced in December 2010.

The difficulties encountered by the production platform, the FPSO Kwame Nkrumah, began with its inability to reach the plateau production of 120,000 barrels of oil per day (bpd) to a level below 60,000pd.

The situation resulted in unsteady revenue for the state and sent shivers down the spine of the investor community, resulting in some shareholders of a partner group going to court. 

The acid

With that came the multi-million-dollar remedial work and additional drillings that did not yield any result and, therefore, the injection of acid that eventually broke the clots for free flow of oil.

Later on, the onshore Western Corridor Gas infrastructure which was to be ready by the time the gas pressure had reached optimum level also failed, which threatened the reservoir.

Until the processing plant of Ghana Gas became operational in 2014 and received gas for processing, the lead operator secured the necessary permits to flare about 15 million standard cubic feet of gas daily.

The compressors

There were also compressor failures and breakdown of turrets in February 2016 when the facility could not export gas to the shore and that compounded the energy problem.

The damage to the turret bearing resulted in many problems for offshore operations, as limited gas supply to onshore power plants forced the partners to come up with new schedules.

It is expected that by the end of 2018, Ghana will master its operational challenges and enough expertise gained to give meaning to its diversification drive, including improved skills, services and other support for the industry.

Turret & spread moored systems

The turret systems are of two types — internal and external — that are commonly used for FPSOs. With the internal system, the turret is mounted within the hull of the FPSO, while for the external, as used by the FPSO Kwame Nkrumah, the turret is mounted on a structure extended from the bow of the vessel.

Spread mooring, also referred to as multi-point mooring or anchoring system, has long been the traditional way of mooring all kinds of ships and barges in open and protected waters.

It is designed to station or keep vessels in shallow or deep-water and in mild to moderate environments and is dependent on prevailing weather conditions. It is considered suitable for regions with a fairly restricted range of weather conditions, as prevail in Ghana and the West African sub-region.

 

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