Directional drilling of wells that deviate far from the vertical has proved a key technology in accessing much of the North Slope’s vast oil reserves. But drilling to horizontal departures of tens of thousands of feet takes you into the world of ultra extended-reach drilling, a technology that could, for example, allow some Arctic offshore oil fields to be developed from onshore or nearshore locations.
BP has successfully used extended reach drilling to develop its Wytch Farm oil field on the south coast of England, where the oilfield facilities lie onshore but a major part of the oil reservoir lies under scenic Poole Bay — wells with horizontal departures of 25,000 feet and more tap oil from the undersea reservoir without the need for any offshore infrastructure.
Drill from Endicott
The company hopes to repeat its Wytch Farm success at the Liberty field, about 5.5 miles offshore under the Beaufort Sea. Liberty development plans envisage a 20-acre expansion to an existing satellite gravel island at the neighboring Endicott field, to accommodate the Liberty drilling rig and wellheads. Production will go through the Endicott facilities and pipeline.
But Liberty drilling will likely achieve world records for extended reach drilling, with horizontal departures from the wellheads of up to 44,000 feet or more.
“Drilling studies support departures of 34,000 to 44,000 feet,” BP has said. “Departures beyond 44,000 feet have not been studied.”
Turning or pulling the drill string in these exceptionally long well bores will require a massive drilling rig. And, having established that there is no existing rig powerful enough for the job, BP is commissioning the construction of a purpose-built rig — construction is slated to start in 2008 with completion planned for the third quarter of 2009.
“We’re looking at a 2010 timeframe … for actual drilling (after) going through permitting, rig design, engineering,” Gary Christman, BP’s director of Alaska drilling and wells, told Petroleum News.
The new rig for Liberty will be the largest land rig ever built in the world, and the exceptional length of the wells will require a raft of state-of-the-art technologies such as rotary steerable drilling.
“It will take all of this technology that we’ve developed and exploited in Prudhoe Bay and extend it to a new realm,” Christman said.
Ingenuity
Manipulating the drill strings down the extended reach well bores will require some ingenuity. For example, the need to use progressively smaller diameter casing as a well penetrates further through the rock will likely drive the need to use tubing that the drillers can expand downhole to the well bore diameter.
And at these depths even the weight of pipe used to convey the bit downhole is a challenge for the rig to handle. To lighten the load, aluminum drill pipe may be used instead of traditional steel drill pipe, Christman said.
“We’ll be doing some field trials with aluminum pipe in Prudhoe Bay,” Christman said. BP also wants to establish a way of re-entering the Liberty wells, to enable the use of sidetrack wells that avoid the need to drill more of the highly expensive extended reach wells than necessary.
And BP plans to test some of the techniques that it hopes to use at Liberty as part of an extended reach drilling program in the company’s Beaufort Sea Northstar field — the Northstar extended reach drilling will enable the company to increase the oil recovery at that field, Christman said. BP started work on its Northstar extended reach wells in the winter of 2006-07 but the company has not yet completed any of the wells.
“The intention is that this winter we will finish those Northstar wells, and knowledge from those wells will be supporting our efforts to be successful in Liberty,” Christman said.
But in venturing into as-yet untried extended reach distances at Liberty BP expects the unexpected.
“The key to us is going to be reacting to problems that we don’t anticipate,” Christman said.
