The Maui A offshore platform is enjoying multiple benefits from a high-tech drilling rig erected on the facility in 2012. These include improved safety, more operational flexibility and better overall efficiency – not to mention a significantly extended lease on life. LAWRENCE SCHÄFFLER explains.
THE ADDITION OF A DRILLING rig to the Maui A platform is, in itself, somewhat unusual. New drilling has been sporadic on Maui A over the last 30 years – the platform extracts gas from wells drilled decades ago and is rarely equipped with a rig. But the new rig – the Emerald Archer – is allowing Shell Todd Oil Services (STOS) to tap into previously inaccessible pockets of gas. The new rig’s also unusual for other reasons. For a start, its deployment on an offshore platform is a world first. Described by the manufacturer (Germany’s Max Streicher GmbH) as a Super-single Rack and Pinion Drilling and Intervention Rig, it’s widely considered something of a breakthrough in offshore platform drilling technology.
Its modular design, developed on the other side of the planet, was one thing – getting it on to Maui was another. Shipped to the platform in stages, it comprises more than 100 individual modules.
Each had to be sufficiently compact and light for lifting into position by Maui’s onboard cranes. Fully-assembled and equipped on the platform, the rig weighs around 1000 tons.
But the Emerald’s most unusual feature is its automated, handsfree operation. A major motivation for ordering the rig, says Owen Hey, head of wells in New Zealand, was safety. And it’s the rig’s rack and- pinion design which provides the automation and the safety benefits.
“Conventional rigs are tall and use cables and pulleys to lift the individual sections of a drilling string into position. The operation involves plenty of manpower in the area below – where the men are assembling the drill string – and it can be challenging.
“A rack-and-pinion rig, by contrast, is hydraulically-operated and is much shorter. There aren’t any pulleys and lifting the 12-metre drill sections into position is largely automated. As a shorter rig it eliminates the need for equipment to be hoisted aloft – the risk of objects being dropped is significantly reduced. “It’s also safer because a hands-free operation requires fewer crew members on the drill floor. The rig removes the human error factor from the equation. Other staff continue to work at distance from the drill floor, ensuring the largely hands-free drill is running optimally.” Furthermore, the actual drilling operation is also fully-automated –a feature that’s brought major operational benefits. As a computerised system it offers precision control over great distances and allows the rig to penetrate areas further from the platform than what was previously possible. In effect, it’s given Maui A a new lease on life.
The Maui gas field extends over 157 square kilometres and lies 3000 metres below the sea floor. STOS extracts gas via two platforms (A & B). Maui A has 14 wells, B has 12. The wells for each are in a grid pattern, about two metres apart.
Mounted on skids on the Maui A platform, the Emerald Archer is easily shifted between the 14 wells.
At Maui A, Hey explains, the wells typically follow a J-bend. “They descend vertically for about 1000 metres before turning and heading off in different directions to the gas pockets. The depth or length of wells is limited by the rig’s power and the better the control, the further this power allows you to go.
“A lot of thought goes into calculating the optimum path to minimise the loads and stresses on a drill string. The wells can be anything between four and seven kilometres long and every bend adds to the load – fewer bends helps to keep the load manageable. “To compound the load issue, the drill head encounters different densities of rock as it moves along, so you need to be able to match the torque and speed of the drill to the rock it encounters – and that needs precision control.”
These issues have limited Maui A’s wells to some 5000 metres or 6000 metres. With the Emerald Archer’s superior control, the wells are being extended to reach new pockets of gas. The longest of the new wells measures nearly 7000 metres.
Precision control has also seen the introduction of aluminium drill sections for the first time, replacing the conventional steel models.
“As a computer-based rig,” says Hey, “the drill’s operation is controlled very precisely. Because the drill string doesn’t move around as much as the conventional version, any sudden loads and stresses on the drill string are eliminated.
“With far lower loads and stresses, we have been able to introduce – for the first time in offshore drilling in New Zealand – aluminium drill sections in place of the traditional, heavier steel. Aluminium pipe reduces the load and results in a better use of power.
“This makes for much greater consistency – it’s a very smooth, steady operation. We are able to dial in 15mm movements over a distance of 6000 metres – that’s unheard of on a conventional rig.”
Hydraulic motors drive the drill and apply a torque of up to 30,000 foot-pounds.
The rig’s automated features include a sophisticated, 24/7 remote monitoring capability, allowing its operation to be assessed from a shore-based team rather than – as was previously the case – having the personnel on the platform itself.
While this feature, says Hey, offers an enormous safety benefit, it also allows the shore-based team to view the operational data in real time to update their calculations.
“It provides an ever-improving kind of ‘feedback loop’, where the team is constantly able to update its models. In essence, the rig’s provided benefits we hadn’t foreseen – predictability makes planning a lot simpler.” The Emerald Archer rig has been operational for 18 months. STOS is renting it from Archer (an international drilling organisation) for a specified programme of work scheduled for completion later this year. It will then be disassembled and shipped to a new location, most likely the North Sea.