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FEATURE Drilling to a truss spar followed in 2005. Seismic, appraisal drilling “One of the things we learned was we had to go slow to and production data increased the reserves in place esti- go fast,” Johnston says.

mate to 5 billion barrels of oil by 2011. Between 2014 and The wells target naturally regressed Miocene sands that are 2016, BP drilled three wells aimed at lease retention and weaker than the surrounding shales. Using the correct mud delineating the reservoir. BP and its partners, BHP and weight keeps the wellbore stable and prevents losses into the

Chevron, sanctioned the Mad Dog 2 project as a stand- formation. But that alone wasn’t the solution. BP found that alone production facility serving 14 production and 8 in- by slowing drilling rates down in these sections, the drillers jection wells and ? rst oil targeted for 2021. created a more stable environment for handling the pressures.

While the spar is equipped to handle both drilling op- “We didn’t see the losses we saw in earlier wells,” John- erations and production, “the ef? ciency of drilling from a ston says. “We went from 200 feet per hour to 70 feet per spar is a lot lower than drilling from a dedicated drill unit,” hour. It’s slower, but it’s safer. It’s a good technique.”

Emembolu says. Another technique that saved time was removing a cas-

Beyond that, the spar limits step-out options. Using a ing string by changing the overall casing design.

drillship provides ? exibility in addition to time and cost One of the ef? ciencies was a result of reevaluating the savings, Emembolu adds. casing design. By reevaluating the pore pressure and drilling

One of the themes for Mad Dog 2 has been price reduc- trajectories, the engineering team was able to safely deliver tion. An earlier plan to develop the reserves, dubbed Big a design that had one less casing string in it than the earlier

Dog, would run $22 billion. The current plan more than wells. This removed the ? at time associated with running halved the price tag to $9 billion. the string and had the added bene? t of minimizing person-

The Mad Dog 2 team has used ef? ciencies such as using nel exposure to handling equipment, Johnston says.

a dual derrick rig, stack hopping and rebasing well design The West Auriga’s dual derrick design further drove ef- along with an integrated performance model to slim down ? ciency with the drilling campaign. The team was also able drilling costs. In a September speech, Bernard Looney, BP to move the blowout preventer during batch drilling with- chief executive, upstream, said, “Well-drilling is down by out bringing it to the surface, to create further time savings.

an average of $46 million per well on Mad Dog 2.” Once Argos is online and receiving hydrocarbons, John-

Effectively, says Glyn Edwards, Mad Dog reservoir man- ston says, BP will study production data for six to 18 months ager team leader, the team has saved a year of rig time while to better understand the ? eld and see which injectors sup- still delivering the same number of wells. port which producers. With that understanding, he says, the “Wells were repeatedly going faster,” Johnston says. One team will drill the remaining wells planned for the ? eld.

of big challenges and big successes of the project to date, he “We have a model today, thousands of models. We don’t says, has been managing the pace of activity to design and really know which one’s right. We’ll learn from the wells safely drill the wellbores through an evolving understand- and production data to see where future wells need to go,” ing of a complex geological environment. Johnston says. “You’re not just drilling a well, you’re drill-

Johnston says the drilling team has had “fantastic” learn- ing a well surrounded by geology. We’ll take our best learn- ing from one well to the next. ings from the subsurface and use that information to in-

And some of the learnings were counter-intuitive. form our forward path and what we do on the next well.”

Mad Dog at a glance

Water depth4,500 feet

LocationGreen Canyon 825, 826, 782

Field discovery1998

Oil in place5 billion barrels

OperatorBP, with 60.5% working interest

PartnersBHP Billiton (23.9%) and Union Oil Company of California, an af? liate of Chevron U.S.A. Inc. (15.6%) 50 OFFSHORE ENGINEER OEDIGITAL.COM