By Gus Morgan
After a two-year break, ConocoPhillips is drilling again in the volatile oil and gas condensate reservoirs of the J-Area in the U.K. Central North Sea. This renewed program includes work on eight development wells and four infrastructure-led exploration (ILX) wells.
“We’re back in the business of development drilling in the J-Area,” said Gerry Cooper, U.K. Well Operations manager. “This new batch of wells is a result of us taking a step back, reviewing and refreshing our portfolio of opportunities, looking at new technology and cutting costs to achieve a competitive cost of supply.”
Andy Leishman, Subsurface manager U.K., said, “it’s a new and exciting chapter in the history of the J-Area. And this chapter was introduced because of the challenges we’ve had over the last few years.”
To date, the Ensco 120 rig has drilled and completed two development wells, S10 and S11, and it is now busy working on S12, an ILX well targeting an undrilled fault block adjacent to the main producing area on Jasmine.
In 2016, development drilling was put on hold because of low commodity prices, unappealing economics and having exhausted the highest-graded opportunities in the portfolio at that time. But sometimes a step back is a step forward.
In this case, the break gave the U.K. subsurface and drilling teams a chance to regroup and rethink their development program for the J-Area, which consists of the Jade, Jasmine, Joanne and Judy fields. While the subsurface team developed a new portfolio of high-graded drilling opportunities, the drilling team focused on reducing operating costs and improving efficiency.
How they did it
Deflation, efficiency gains and technology have all played a part in lowering costs, resulting in a roughly 40 percent reduction in well development costs from 2014. However, one of the biggest game changers involved the use of seismic imaging, which dramatically improved the image quality. Such imaging allowed a better understanding of a complex geological structural environment, reducing risk and enabling better investment decisions and optimization of well placements. Together such moves have resulted in a competitive cost of supply of less than $25 per barrel.*
Leishman said data from an ocean bottom node/compressive seismic imaging (OBN/CSI) survey in 2014-2015 was combined with other OBN surveys acquired in the region.
“We reprocessed everything and managed to improve the imaging of the reservoirs and refine our view on targets,” he said.
The improved imaging also gave the team a chance to present several new exploration opportunities to Richard Lunam, president, Exploration, Subsurface & Other International. Those ILX drilling opportunities are now part of the current campaign. They also helped the team step into the 30th U.K. licensing round, where they picked up three additional licenses.
S10 targets the Paleocene
The first well of ConocoPhillips’ J-Area redevelopment campaign, S10, took 160 days to drill and complete.
“S10 is one of the best Paleocene wells we’ve drilled, with excellent productivity,” Leishman said.
S10 is extracting additional volumes from the Joanne Paleocene field that first saw production in 1995. Originally thought to be fully depleted, new data and subsurface analysis unearthed opportunities to redevelop. “It’s a great example of a field that wasn’t fully depleted, coming back two decades later, redeveloping it and extracting more value,” Cooper said. “This has come about because of a combination of an improved subsurface understanding and innovative new completion techniques.”
Drillers used managed pressure drilling (MPD) and geo-steering to create a 4,000-foot horizontal section in the thin sandstone reservoir. Deep-reading resistivity tools allowed them to image 50-100 feet around the bit, allowing the well to be geo-steered to remain in a zone only about 8-10 feet thick.
Akin to threading a needle, this precision drilling enabled them to land the well accurately in the reservoir and remain in the reservoir for a larger percentage of the horizontal production bore section, optimizing drainage and helping to maximize well productivity.
During completions on S10, ConocoPhillips also took a new approach for the J-Area, using open-hole sand screens, to better manage shale and sand ingress on S10, keeping the wellbore from clogging and improving reservoir productivity. Sand screen completions are planned for all future Paleocene wells.
Efficiency has been the cornerstone of this drilling campaign. Flowline hook-up and commissioning and well handover to first production took only 14 days, a 24-day improvement over the previously drilled well S9.
Challenging the drilling envelope
Shortly after finishing S10, drilling started on S11, a deep Triassic well that took around 110 days to drill and complete.
Well control technical aspects were a challenge because S11 was drilled in a high-pressure, high-temperature reservoir penetrating multiple production zones ranging from near full pressure to highly depleted zones.
Because the Jasmine reservoir was already significantly depleted due to ongoing production, it was initially thought to be technically undrillable.
“However, MPD allowed us to control the effective wellbore pressure and create a very narrow operating window where the well could be drilled,” Cooper said. “Without that technology we wouldn’t have been able to drill the well using conventional techniques.”
A challenging environment
“J-Area has a complex geological make-up,” Leishman said, “and coupling that with pressure depletion associated with ongoing production means that it isn’t an easy environment to extract value from. The work Gerry and his team have been doing is cutting edge.
“The J-Area campaign is being treated as a portfolio of opportunities. Due to the subsurface and drilling complexities, we may have one or two challenges and disappointments along the way, but hopefully these will be balanced by upside occurrences, and we are excited about this portfolio as a whole.”
ConocoPhillips U.K. sees the drilling campaign as an opportunity to create a step change in production overall.
A big part of this potential production increase is the planned J-Area ILX wells. The group has just started drilling on S12, an ILX well that targets a fault block that hasn’t been penetrated yet, as part of an effort to extend the life of the field. This is the first of four ILX wells to be drilled over the next three years, and they all have the potential to add relatively significant volumes to J-Area in years to come. Upon success, S12 would be immediately completed and brought on line.
“If you look back to where we were in 2015-2016,” Cooper said, “I think there was a serious concern whether we would go back to drilling in the J-Area at all. Now that’s turned around and everything’s looking decidedly more upbeat.”
*Cost of supply is the West Texas Intermediate equivalent price that generates a 10-percent after-tax return on a point forward and fully burdened basis. "Fully burdened" includes capital infrastructure, foreign exchange, price-related inflation, and general and administrative expenses.
- U.K. Central North Sea
- Fields include Judy, Joanne, Jade and Jasmine
- High-pressure/high-temperature gas condensate Triassic, volatile oil chalk and gas condensate Paleocene reservoirs
- Consists of offshore conventional wells