As technology has improved, so the applications have increased — and now this drilling method is approaching the mainstream.
SOPHISTICATED managed pressure drilling (MPD) applications have helped operators tackle difficult wells in places including West Africa and Brazil’s pre-salt, and it is now making inroads in the deep-water Gulf of Mexico.
Based on the precise manipulation of downhole pressure via instruments instead of the traditional approach relying upon the weight of drilling mud, Marathon Oil recently used MPD to drill its Solomon wildcat in the Walker Ridge area of the US Gulf — a first-of-its kind application of the technology on a deep-water floater in the region.
It was the first time MPD had been approved and utilised with a subsea blowout preventer system in the US Gulf, says a Marathon spokeswoman, adding that the company has previously used MPD with a subsea BOP outside the region.
Chevron has also recently run promising preliminary tests in the deep-water US Gulf utilising single-gradient subsea mudlift drilling, a form of MPD, according to results presented at the 2015 Society of Petroleum Engineers annual technical conference.
“It’s a very, very powerful tool for deep-water wells that we are drilling today,” drilling engineer Sharifur Rahman told an audience.
Proponents of the technology see this as only the beginning for MPD in the deep-water US Gulf, believing it has safety, timing and reservoir advantages, especially as operators tackle difficult geologies such as the Lower Tertiary trend and other high-temperature, high-pressure reservoirs.
Exciting time “It’s a growth industry,” says Brian Grayson, director of pressure control systems for secure drilling services at Weatherford International , who has worked for more than a decade with the company on developing the technology.
“It’s seeing quite a bit of acceptance. It’s an exciting time.”
MPD traces its roots to underbalanced drilling, which came to the fore in the mid-1990s.
Underbalanced drilling also worked with a decreased mud weight, but pumped nitrogen and foams downhole to keep pressures up while simultaneously flowing hydrocarbons.
This served to maintain well pressure while preventing mud from leaking into the formation and affecting the porosity of the rock, averting potential reservoir damage.
The technique was used onshore in Canada, in the US Rocky Mountain region, the Middle East and North Africa.
It was used on a handful of North Sea jack-ups, but was limited for offshore applications by the amount of equipment required for pumping and offloading.
That need helped spur the development of MPD, in which specialised equipment — a rotating control device as well as a surface back pressure choke system — would be incorporated into the rig’s existing well-control kit.
“We started to identify that we can drill fairly conventionally, except instead of just pure mud weight, like you’re used to… we can use the weight that we induce from surface back pressure,” says Grayson.
Companies such as Weatherford started applying these technologies in the early 2000s.
The early systems were manual, operated by an engineer on the rig floor tasked with making calls about what the pressure should be.
“You looked at a surface pressure gauge and based on calculations you opened or closed the choke to manipulate that surface back pressure,” Grayson recalls.
Making a difference The company then went on to develop semi-automatic systems in which the choke would oscillate and open and close on its own to maintain a certain established pressure.
“We are getting more automated every day,” says Grayson. “So now the system itself is identifying on its own what the bottom-hole pressure is and what it needs to do at surface to maintain that.
“The systems are now automated to the point where they can identify kicks and losses on their own and react to them.”
Early MPD applications were slow to catch on offshore, although some US Gulf jack-ups used the technique.
But eventually companies started trying it when nothing else would work.
“This was the last-ditch effort,” recalls Grayson. “It was drilling the undrillable.”
The technology is especially useful for wells with very small margins or limited leeway between the pore pressure and fracture pressure, at which point the formation risks collapse.
Typically, changing pressures downhole requires a change in mud weights, requiring the circulation in of the lighter-weight fluid, a process that can lead to swings in pressure.
With MPD, the goal is to never see much of a pressure difference in the bottomhole, with variations of less than 25 psi measured during well connections, according to Grayson.
That can “make all the difference in the world” on tricky wells, he says. Proponents say companies found MPD helpful not only in tackling the reservoirs but also in efficiency and safety, such as drilling through difficult zones more easily. Some have applied the technology for its monitoring benefits.
New targets Brazil’s Petrobras has been an early adapter, especially on pre-salt reservoirs.
In those wells, the risk of fluid loss is exacerbated by the weight of huge drilling columns sometimes exceeding 6000 metres, Upstream previously reported.
“We have been reaching targeted bottom depths on wells that probably could not have been drilled otherwise,” Emmanuel Franco, a senior Petrobras petroleum engineer, told an industry seminar recently.
Petrobras aims to have 16 of its rigs equipped for MPD work during the course of this year.
Growth projection data for MPD are scarce, but one study published this year from Markets to Markets anticipates total market value growing from $11.5 billion in 2014 to $16.9 billion in 2019.
Today’s prolonged oil-price downturn may make it more difficult for technology providers to make their case, though proponents argue the technology may pay for itself in efficiencies gained.
Other operators have been content to handle even the region’s trickiest plays using their ordinary drilling kit.
However, attention is being paid to US Gulf jobs such as the Solomon well, says David Pavel, who chairs the International Association of Drilling Contractors committee for MPD and underbalanced drilling in the region.
“The reception of MPD in the operating community is becoming much better,” says Pavel, who is also president of consultancy Welling & Company.
“My opinion is that it’s certainly moving closer to the mainstream.”
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