A new direction in CwD
  from: Offshore Engineer
  by: Jennifer Pallanich
  Friday, May 16, 2008

Adding a retrievable bottom hole assembly to offshore directional casing while drilling seemed a good way to address the lost circulation and wellbore instability issues accompanying drilling through depleted zones that are a bane of offshore brownfield construction. After establishing that the casing while drilling directionally technology works on land and eliminates the need for drill string tripping, one operator took the technology to the North Sea. US editor Jennifer Pallanich reports on the technology and its journey to the offshore Eldfisk Bravo platform.

Historically, the industry has produced reservoirs that are easier to reach before searching deeper in the ground. Every barrel of oil the industry pulls out of the ground increases wellbore instability issues by creating man-made trouble zones.

While drilling a section of a well with casing is not entirely new, only recently has it become reliable and accessible. In the late 1990s, along came vertical casing while drilling (CwD), which can improve the mechanical stability of the wellbore via an effect referred to as plastering or smearing that strengthens the wellbore wall.

‘If you’re drilling while casing, you’re able to drill through a lot of trouble zones,’ says Nigel Lakey, Tesco senior vice president of marketing and business development. Since the 1990s, the technology has evolved, and it is now appropriate for vertical and directional applications, he adds.

That’s just what ConocoPhillips wanted to do. About four years ago, ConocoPhillips was looking for a solution that combined CwD with a rotary steerable system (RSS) with an eye to harnessing the advantages of CwD and directional drilling for offshore applications, says Rick Watts, ConocoPhillips drilling engineering fellow.

That meant combining a RSS with CwD to yield capacity to drill directionally. The other requirement was to retrieve the BHA while leaving the casing behind. ConocoPhillips, Schlumberger and Tesco did some directional CwD (DCwD) work at a ConocoPhillips field – Lobo in Texas – in 2004. A big concern was downhole vibration. Because casing acts as a dampener at the surface, ‘things can be vibrating wildly downhole and you’d never know it,’Watts says. Such was the case at the Lobo field,where there were several tool failures related to vibration issues,Watts says. Two CwD tests at Schlumberger’s facility in Cameron, Texas, followed, leading to an easily implementable stabilization methodology that eliminated the vibration problem, he adds.

It was time to go offshore.

To find a suitable well, it was important to remember what hole problems needed to be solved before applying CwD as the solution,Watts says. ConocoPhillips had a challenging sidetrack well off Norway that it wanted to drill from the 30-year-old Eldfisk Bravo platform.

‘You’ve got to understand where you’re going for collision reasons,’Watts says. ‘We took on a very challenging well.’

Bill Lesso, Schlumberger drilling mechanics advisor for drilling and measurements, says the Eldfisk well was an ‘indisputably moderately difficult fully directional well with turns over long distances’.

Parameters in Norway included tight clearance, complex directional drilling with a 130° turn and building up to 22° from vertical, in one BHA run. The November 2006 sidetrack well included 10 3/4in and 7 3/4in casing strings that were successfully drilled directionally through the overburden section. Most running and BHA retrievals were done with wireline using a purpose-built traction winch system rated to 40,000lbs. There were also a couple of drill pipe retrievals. After cementing the 7 3/4in production casing, the casing string was converted to a production liner with an expandable liner hanger, and the upper section of the string was retrieved.

In the well, 10,968ft of 13,600ft were done with DCwD.

Pre-drilling modeling and testing yielded predictable results regarding hydraulics and torque,Watts says. Despite variable torque loss in drilling the well, he says, the well still reached the planned end point. He adds the company was able to drill with the lowest mud weight used in the area in nearly a quarter century.

Plastering, which mechanically strengthens or alters the wellbore wall, is not well understood, but it appears to happen through CwD; further, there is no quantifiable evidence of the plastering, Lesso says.

According to Lesso, it’s not yet been figured out how to measure or quantify the plastering effect.

What is known, he says, is that plastering seems most likely to happen and help in depleted environments and where instability issues exist. Lesso says he’s working to come up with a quantifiable relationship using physical properties to determine if a certain technology is applicable to a certain environment.

‘Not everybody is convinced it is this plastering effect,’ says John Cadiz, global product champion for CwD at Halliburton’s Sperry Drilling Services, ‘but something is definitely going on.’ Cadiz, who says he does believe the plastering effect exists, says it’s important to keep the stickout below the tools as short as possible to get the plastering effect as soon as possible.

‘We had a very stable wellbore,’Watts says. ‘Plastering, smearing, whatever you want to call it, I’m convinced it’s real, and we know how to get it when we want it.’

Surface DCwD equipment includes a split bock, swivel with space for the wireline BOP, top drive system, Casing Drive system and casing. Downhole tools include casing profile nipple, drill lock assembly to connect the BHA to the casing, straight PowerPak, underreamer, Slim Pulse MWD, Power Drive XS RSS and a fixed cutter bit. Lakey sees the paired technology of DCwD and RSS as a viable solution for offshore drilling requirements.

Steerable system motors couldn’t handle the chore, as evidenced by work onshore in Mexico and Brazil earlier in this decade, Lesso says. Applying RSS to onshore DCwD wells seemed to make the difference. ‘It worked, with problems that over 2005 and 2006 we resolved,’ Lesso says.

Watts says the Eldfisk work shows that DCwD is technically feasible offshore. ‘We were proving the concept.We verified that we have the capability of drilling with full directional control.’

Watts says ConocoPhillips plans to use DCwD in high cost environments like the GoM and the North Sea; while the operator has yet to commit to further offshore work, it is considering potential sites.

He acknowledges that DCwD has some challenges, such as the motor. ‘We need a little help from the motor designers to get past this problem.’

Another area that needs attention,Watts notes, is in portability. ‘That’s a barrier to entry for this technology,’ he says, noting the company had to modify the platform by installing equipment needed to run the DCwD system. Currently, the retrievability of the BHA is based on the wireline. As it stands, the system is not right for use on a jackup or a one-off well. He says CwD does pose the issue of a limited reach due to the larger and heavier tube, which translates to a need for upsizing on the topsides and connections.

Lesso says wireline retrievability is the main impediment to introducing DCwD offshore because of the need for a large space to accommodate the winch, which is why retrievability with drillpipe is becoming popular. ‘I think we may move almost exclusively toward drillpipe retrieveability because it requires minimal rig modifications,’ Lesso says.

Finally, vibrations will always be a concern. Lesso says Schlumberger has worked in its US test facilities to reduce shock and vibration, but concerns remain.

Technology evolves

Arco (Atlantic Richfield) earned a patent on CwD in the 1990s, and Tesco later bought the patent from Arco. Since then, Tesco has developed new technologies to combine with the original patent. Throughout the late 1990s, Tesco carried out a number of drilling projects in Calgary where the company ‘fine-tuned the initial generation of CwD tools,’ Lakey says. To support that effort, he adds, Tesco also built equipment. In 2000, prototype equipment performed some jobs, which led to commercial levels of work.

‘Essentially, we found ourselves in the casing business,’ Lakey says. ‘We clearly demonstrated you could drill (onshore) wells with casing.’

There was room for improvement.

‘What we began to learn, to actually get a system, a whole solution that’s predictable and reliable, that’s where the real heart of the challenge lay,’ Lakey says.

Over the next few years, he says, Tesco overcame a number of little failures to make incremental improvements in its Casing Drilling processes. The company has invested over $50 million and six years to develop the system. It has global nonexclusive joint marketing agreements with Halliburton and Schlumberger to enable the effective combination and delivery of late generation RSS, MWD and LWD technology with the Casing Drilling system. ‘Our business is not directional drilling,’ Lakey says, ‘rather it’s the conveyance of tools and technology that allow the well to be drilled with casing. So, we have aligned our process with industry leading solutions from trusted providers.’

‘The failures we’ve had have been in components, and not with the system,’ Lakey says, adding none of the problems could be considered a train wreck. ‘There’s usually three, four, five, six, seven generations of something before it’s released.’ The evolution of Tesco’s Casing Drilling system tracks that.

Anticipating need, Lakey says, ‘we started doing directional work very early in the process’. ConocoPhillips later came knocking, Lakey says, looking for a specific drilling solution: ‘A drillable steerable retrievable liner system is really what was being asked for.’

Tesco determined a number of challenges exist with using conventional steerable motors in DCwD, especially when it comes to motor performance and torque. The flip side, however, is the cost associated with using a rotary steerable system, which in its infancy was not yet reliable, Lakey adds. He notes the technology needed to meet ConocoPhillips’ requirements offered some beneficial side effects, like lower horsepower needs and lower torque requirements.

Historically, about 80% of CwD has been done with a non-retrievable bit on the bottom of the casing, leaving the bit in the hole. The retrievable BHA aspect of DCwD makes it a viable alternative to conventional directional drilling in brownfields with lost circulation and wellbore stability issues, Tesco says.

DCwD uses a more complicated BHA than is usually found on a standard vertical drilling BHA, Lesso says. The DCwD BHA is 55ft longer and weighs twice as much as a standard BHA, he says. Directional drilling is not practical unless it’s possible to retrieve the BHA at will, Lesso adds.

CwD is said to reduce the need for expensive mud additives, eliminate BHA tripping for swab and surge problems, decrease time and trouble while running casing, and create a better hole, which yields better cement jobs and completions, says Kyel Hodenfield, Schlumberger vice president of technology and marketing.

‘It allows you to drill wells in trouble zones that you could not drill any other way,’ Hodenfield adds.

DCwD allows circulating while running the BHA into and retrieving it from the well, which improves well control, Tesco says. Lakey calls the DCwD process reliable and predictable.

‘I believe casing drilling will become a niche product. It will be used mainly in troublesome areas, but the market is definitely growing,’ notes Cadiz. Halliburton’s Sperry Drilling Services first entered the casing drilling market in 1998/99 when it developed and tested a system. Sperry exited the market and Halliburton re-entered the CwD market about three years ago.

Tesco’s DCwD is available for 7in, 9 5/8in and 13 3/8in casing and for 4 3/4in to 8in RSS. Tesco’s Casing Drive System works with top drive drilling rigs and can circulate, reciprocate and rotate the casing string simultaneously. Lakey says the DCwD technology can work in a subsalt environment, with monodiameter drilling, underbalanced drilling, managed pressure drilling and horizontal drilling.

‘The technology itself lends itself to almost any drilling environment,’ Lakey says. ‘The sweet spot for this technology is deepwater,’ where spread costs and risk reduction are driving forces, he adds. Both DCwD and or close tolerance liner drilling (CTLD) can provide significant cost and performance gains, he notes. ‘The technology has been reasonably well taken up offshore,’ Lakey says, noting most interest is for brownfield use rather than exploration. ‘We don’t care if it’s an exploration tool or a brownfield tool.’ The technology works, he says. It’s just a matter of where it makes dollar sense.

Tesco’s DCwD backlog includes offshore work for a number of E&P companies, around the world in mature regions.

Liner drilling

Tesco is working on CTLD with the goal of reliably drilling a liner directionally, Lakey says, because this would give the opportunity to drill through a trouble zone and save the wellbore. It doesn’t hurt, he says, that liner drilling is in high demand.

‘If you can drill with a liner, you can do anything,’ Lakey says, adding that the goal is attainable but not simple. ‘There are probably six or eight ways it can be done. It’ll probably be like Betamax and VHS,’ he says, referring to the VCR race for market dominance in which VHS upstaged Betamax, the initial market entrant.

Cadiz notes operators have had problems getting liners to the bottom. The industry wants a retrievable BHA, but no company has yet commercialized a liner drilling system using a retrievable BHA, he adds.

A steerable retrievable liner system is ‘within our grasp,’ Lakey says. ‘That demand is clearly here, and it’s here now.

‘It’s the Holy Grail of drilling,’ he adds, ‘and we’re getting closer every day.’ OE

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