The key to unlocking Kikeh
  from: Asian Oil & Gas
  by: John Mueller
  Thursday, August 24, 2006

Kikeh, Malaysia's first deepwater development, will boast both the first spar platform outside the Gulf of Mexico and the premier application of a tender assist drilling unit (TADU) with a spar. John Mueller reviews the thinking behind this novel combination.

The Kikeh spar will support a dry tree unit riser system with a TADU for field development drilling, connected by a new tandem mooring system.

The Kikeh spar design is being undertaken on four continents and coordinated in Kuala Lumpur, Malaysia, where the hull and topsides are also being constructed. The spar configuration, fabrication methodology and field installation plans were developed by Technip technology centres in Houston, Perth, Paris and Pori, Finland, with technology transfer to Malaysia project management.

Hull transport to the Kikeh field will be via a combined dry and wet tow operation, with topsides installation at the Kikeh location by floatover.

The match of a TADU and spar-based dry tree unit is a first case application that poses the challenge of designing a tandem mooring system to control the relative movement of the two vessels during various conditions such as the TADU rig-up phase, normal operations and pull-back mode in extreme environmental situations.

Spar bright
The spar concept has evolved through application entirely in the Gulf of Mexico. Kikeh is employing a truss spar, which essentially consists of a cylindrical, compartmented upper section, the hard tank, for buoyancy and a lower section composed of a space frame truss with several fully plated horizontal levels, known as heave plates, to trap the mass of entrained water in a wave surge. Also, at the bottom of the truss, is a soft tank, a plated-steel structure that provides buoyancy at the keel when the spar is towed out in a horizontal position. The soft tank includes compartments for high density fixed ballast, which is added offshore. This configuration results in very low heave and pitch motions in extreme weather conditions.

Variable seawater ballast in the bottom of the hard tank adjusts draft and trim for major variations in topside loading, as for a top tension riser.

Superior floating stability results from the centre of gravity being located well below the centre of buoyancy, without reliance on the mooring system, allowing installation of top tension risers with dry trees.

Drilling from a spar platform is unique in the sense of being able to have the drilling riser permanently installed during development drilling. This is achieved by utilising a dedicated drilling slot on the spar and incorporating a drilling riser parking position on the seabed. This means that the drilling riser does not have to be pulled when running production riser or completing wells.

The spar hull and topsides for the Kikeh field, held by Murphy Oil Corporation (operator) and Petronas Carigali in a 80:20 venture, are being fabricated by Malaysia Marine & Heavy Engineering (MMHE) at its yard in Pasir Gudang, Johor, about 800 miles from the project.

The contract for the dry tree unit engineering, procurement, installation and commissioning was awarded to Technip Marine (Malaysia), with construction at MMHE.

The Kikeh development, situated in the southern part of Malaysia's block K - and its first deepwater discovery - has a recoverable reserve base in excess of 400 million barrels. The spar will be delivered to the Kikeh field in late 2006 with first production expected in 2007.

The truss spar hull will have a diameter of 106ft, overall length of 465ft and draft of 430ft. The payload of 10,500t includes the topside, risers and the drilling/workover rig.

The seabed well pattern for Kikeh consists of a circle 156ft in diameter while the well slots on the platform are located in a five by five configuration with an 11ft spacing. The spar has 24 slots arranged in a circular layout for production/water injection risers and a dedicated centre opening for the drilling riser. When drilling wells, the whole spar moves over the subsea wells to achieve alignment. In tieback mode, the drilling equipment set is skidded over a surface well location and the spar positioned to align the surface well slot, with drilling equipment set, and the subsea well.

An API standards spread mooring system will be made up of 10 lines of chainwire-chain in four groups, designed to handle extreme 100-year conditions with a single mooring line failure.

The Kikeh spar will utilise the Smedvig semisubmersible West Setia to provide tender assist drilling services for field development for two drilling periods of about 39 months and 24 months. West Setia, a two pontoon and six-column semi, has cranes for lifting the self-erecting DES on to the spar in several packages, weighing up to 240t.

A personnel gangway will be provided between the spar and TADU.

The West Setia will be moored to the seafloor by four mooring wires from four winches and fairleads on its aft columns and connected to the spar using a fourline lashing system.

Nylon hawsers will provide stretching capability to absorb the relative motions between the TADU and the spar, mounted vertically along the hull of the spar.

Model tests for the Kikeh spar were conducted at Force Technology in Denmark in two campaigns, testing the spar alone and with the TADU in close proximity for several environmental headings and for a number of one-year, 10- year and 100-year wind, wave and current events. In total, more than 100 different cases were tested.

Compared to a subsea development with wet trees, a spar-based dry tree wellhead platform provides many benefits. A wet tree requires expensive subsea flowlines, and more costly risers and subsea trees than dry tree completions. In addition, the wet tree drilling operations have to be carried out by a mobile offshore drilling unit (MODU) with limited availability and high dayrates which not only impacts initial drilling but also subsequent well activities, typically resulting in fewer interventions and consequently less total oil recovery.

Drilling from a spar is more efficient than from a MODU resulting in a spar requiring fewer days to drill and complete each well. A single derrick MODU, for example, has to run and retrieve the drilling riser between each well whereas a spar does not.

For a large drilling programme, 20 wells in the case of Kikeh, high MODU dayrates and additional days per well result in a wet tree drilling Opex that is substantially higher than the Capex plus Opex for a spar supported drilling system.

A further advantage with a spar dry tree unit is the higher overall oil recovery as a consequence of having lower-cost direct access to the subsea trees. Economic analysis demonstrates that, if the aerial extent of the reserves permits drilling from a single location, a spar dry tree unit is more cost effective than a wet tree development requiring a MODU.

Regional choice?
The Kikeh spar may be an optimum deepwater drilling and production system for Southeast Asia.

Prior to Kikeh, the concept of spar drilling took one of three approaches: