Making The Most Of Marginal Field Developments

A starring role for CoSMOS offshore Malaysia.

Marginal fields can be challenging for oil and gas operators. One of the main issues is maintaining tight and effective cost control during field development and decommissioning. A solution that operators can turn to is 2H Offshore’s CoSMOS (conductor-supported minimum offshore structure) system, which is designed specifically for developing shallow-water marginal fields.

The customer featured in this case study had signed a small field risk service contract with Petroliam Nasional Berhad (PETRONAS) for developing and producing oil from a field cluster offshore Malaysia. The fields in this cluster are located within 20 km of each other in water depths of about 60 m. When the operator was looking for a cost-effective field development method, it identified the CoSMOS system as the most appropriate solution.

A CoSMOS system provides minimum facilities or wellhead platforms supported on well conductors. Its innovative design is ideal for marginal field developments, satellite developments, early production infield drilling and additions to existing platform infrastructure, as Shreenaath Natarajan, technical director, 2H Offshore explains. “The system typically uses four well conductors as structural supports but can also be configured with more conductors with single or splitter wells to suit specific applications. CoSMOS is designed for applications in water depths to 70 m and offers high flexibility for operators: it can be hosted by existing platforms, tied back to onshore processing facilities or used for standalone platforms tied into existing field infrastructure.”

Installation benefits
“The flexibility and modularity of the CoSMOS system are perfect fits for an industry that demands cost-effectiveness and schedule efficiency. Operators can install conductors and the associated structures, including the topsides, directly from a jackup drilling rig without using a heavy-lift vessel,” says Natarajan.

“Using conductors as structural elements to support the topsides reduces the need for expensive and potentially complex jacket installation thereby simplifying the procurement and installation processes. In addition, the topside design can accommodate the full range of production and process equipment typical of a minimum facilities platform. The modular nature of the design makes the system suitable for a range of water depths and well counts, and means we can tailor it to suit any specific fabrication and installation requirements,” he continues.

2H Offshore responded quickly to the operator’s request for a CoSMOS system in what was a fast-track project. “We started work on the project in February 2013,” Natarajan says, “and, within three months, had completed the engineering drawings required for fabrication. Fabrication lasted three to four months and the system was ready for transportation offshore by the end of August.

“We worked with the construction yard and the boat that would deliver the structure to ensure that there was no need for a crane barge offshore and that full and effective use was made of the jackup rig’s capabilities. We also defined the installation procedures, oversaw the installation tasks and helped the offshore crew to complete the installation programme,” he continues.

The system was installed in September 2013 as a freestanding unit ready for the arrival of the mobile offshore production unit (MOPU) for hook-up and a production start date in November. Severe monsoon weather delayed the arrival of the MOPU, but the initial connection was made in December 2013 and the final connection was in January 2014.

More efficient decommissioning
By leaving the conductors freestanding, an operator can bring in the MOPU when it is ready to start production. This makes the best use of available resources and means that the installation of conductors does not delay a project. For many operators, a key benefit is the added flexibility that this brings to field development schedules: a crucial consideration for operating companies that may be juggling limited resources and asset bottlenecks.

Early and cost-effective installation is, however, only one side of the coin. The CoSMOS model also provides substantial benefits during decommissioning. Once production from a marginal field starts to decline, it can take a very long time to cease. Although there is still value in extracting a few hundred barrels of oil a day, this value does not stack up against the cost of maintaining an MOPU on the field. With a CoSMOS system, an operator can move the MOPU off the mature field to a more prolific and commercially viable asset at any time and leave the conductors freestanding for subsequent decommissioning.

This flexibility gives operators more control over the timing of decommissioning and enables them to maximise the efficiency of their plans and operations across the life of a field. It is possible to modify conductors to be freestanding at a later stage of a field’s productive life, but this can be an expensive retrofit and may not be an attractive option when revenue from the field is decreasing.

Facing up to fatigue
One of the key issues with installing a freestanding conductor structure is assessing how it will cope with fatigue in its intended environment. This requires detailed analysis of the structure to evaluate vibration effects and wave and current loading and their potential to influence failure at welds and other key parts of the structure. In this case, modelling analysis revealed potential fatigue hot spots in the structure, which 2H Offshore reinforced for added rigidity.

This design approach is possible through combining class-leading marine structural design methods with drilling and conductor knowledge developed over 20 years. The result is a production platform that meets the market’s need for a reliable, low-cost and fast-track solution for shallow-water fields.

The CoSMOS concept uses field-proven technology and this is a vital part of its commercial appeal. “Applying a field-proven system means that we can deliver a low-cost, fast-track solution that is optimised for specific client needs,” Natarajan concludes.

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