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Developing modular drilling rigs - Archer

Friday, February 12, 2016

Oilfield services company Archer is employing harsh environment modular drilling rigs (MDRs) for offshore platforms, which split into modules of less than 12 tonnes.

This means they can be transported to and installed upon offshore platforms without requiring heavy lift vessels.

The MDRs are primarily designed for cased hole drilling, well intervention, workovers and plug and abandonment operations (isolating old wells and recovering spent tubulars and casings). They can also be used for drilling new wells.

The MDRs are particularly suitable for applications where the existing platform drilling rig (if there is one) requires significant reactivation or investment due to either age or prolonged idle periods in a harsh offshore environment.

Choice of rig

If an operator wants to drill new wells or carry out intervention on old wells beneath an existing offshore fixed installation, and the existing platform drilling rig has not been used for a long time or is in a state of disrepair, there aren't many options.

The platform operator has a choice of reactivating the existing rig, bringing in a mobile offshore drilling rig alongside the platform (such as a jack-up rig), or installing a new drilling rig on the platform (such as a modular rig provided by Archer).

Costs for this reactivation activity in mature regions such as the North Sea have spiralled in recent years, as many platforms are more than 25 years old. In some cases, recent reactivation costs have exceeded £25m, says Kevin Cowieson, Business Development Manager with Archer. There can also be problems with obsolete components and scope changes due to unexpected issues, which have a major influence on cost and project timelines.

A jack-up rig can only be used alongside a platform if the water is shallow enough and the seabed conditions are suitable. In addition, the layout of platform structures can prevent it from reaching all of the well slots.

For deeper waters, heavy duty jack-up rigs with upwards of 400ft water depth capability can be extremely expensive.

So building a temporary drilling rig on the platform, such as Archer's MDR, could prove a very cost-effective option.

The MDR rates are generally 40 per cent or more lower than the cost of drilling with a jack-up, Mr Cowieson estimates.

The modular rig

Archer's service model is to build, lease and operate the MDRs, charging by the day.
The rig is entirely automated, with no personnel required on the rig floor in normal operating modes.

It can be run with a crew of as few as 16 people on a 24-hour basis. But Archer typically sends a crew of 21 to the platform to ensure maximum operational efficiency.

Much of the technology in the Archer MDR was originally developed for onshore use. However, Archer - in cooperation with its manufacturing partner - sourced, replaced or optimised the equipment to both withstand and comply with offshore harsh environment operations.

The rig has an alternative tubular conveyance system compared with traditional units. It is a rack and pinion system, which moves the drilling tubulars in and out of the well, rather than a traditional draw works and drill-line system. Statistics show that this technology has a very good performance and safety record.

In designing the MDR, Archer set a weight limit of 12 tonnes. This is a weight that can be transported on a standard offshore support vessel, negating the need for expensive heavy lift vessels. In most cases, it can be lifted onto the platform with a standard offshore platform crane. If required, a modular platform crane can also be deployed.

There are some unique and patented features on the rig. For example; the construction of the mast is similar to how construction cranes are built, pushed up from below, removing the need for cranes with long booms and personnel working at height. In addition, container ship 'twist-lock' lashings have been adapted for quick installation of the support modules.

Typically, it takes four to six weeks to mobilise, rig-up and commission the MDR offshore, Mr Cowieson says.

New Zealand and Norway

In 2012, the first contract was agreed to install one of Archer's MDRs on Shell Todd Oil Services Limited 'Maui A' platform, located in the Tasman Sea off the coast of New Zealand. Between 2012 and 2014, the Archer Emerald drilled a series of wells, with the longest - 'Adi-Thi'- being 6.6km, a record for New Zealand from a fixed (non-floating) installation.

The second contract is on Statoil's Heimdal platform offshore Stavanger. The rig was built to order for this contract.

The rig was delivered to the platform in 11 platform supply vessel sailings over 37 days. The rig-up time was lengthened due to bedding constraints on nightshift. Normally, construction can be achieved in three to four weeks, or quicker if there is sufficient bed space and a large capacity platform crane.

As of September 18th 2015, the rig had completed 11 wells and was 55 days ahead of schedule.

Associated Companies
» Archer
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