BP stemming production declines in Prudhoe Bay

British Petroleum has stemmed production declines in the Prudhoe Bay field on the North Slope for the third year in a row. Prudhoe produces about half of total North Slope oil output, so performance of the 40-year-old field is critical to supporting overall production on the slope, which has shown small increases over the last two years.

In 2017, Prudhoe maintained an average of 280,000 barrels per day, down only slightly from 280,700 barrels per day in 2016 and 281,080 barrels per day in 2015, according to Scott Digert, BP¹s subsurface manager for Prudhoe and Jennifer Starck, BP¹s Prudhoe production manager.

BP is the Prudhoe field operator on behalf of itself and other owners, mainly ConocoPhillips and ExxonMobil.

Increases at other fields on the slope, particularly the CD-5 drillsite at the ConocoPhillips-operated Alpine field west of Prudhoe, added to overall slope production and pushed 2017 Trans Alaska Pipeline System throughput to an average of 526,000 b/d, up 1.5 percent from 2016.

“We¹ve seen no decline for three years at Prudhoe and we¹re quite pleased about that,” Digert said. Prudhoe, still among the largest oil fields in North America, was experiencing annual declines of about 5 percent until BP developed strategies to mitigate the effective decline.

Digert said Prudhoe field operators even beat their own internal targets for 2017, Digert said Earlier in the year BP expected to average only 265,000 barrels per day for the year.

The halt to production decline was achieved despite the sharp drop in crude oil prices in 2015 and BP¹s reduction of drilling rigs in the field from five in 2015 to two in 2016 and 2017.

Production is typically maintained by keeping rigs operating and drilling more producing wells but despite its layoff of rigs, which BP had to do to cut costs, the company has been able to keep up production through a variety of projects that stimulated output from existing wells without using a rig. There were 500 of these non-rig wellwork jobs done in Prudhoe in 2017, up from 430 in 2016.

Digert said there was also relentless focus on the operating efficiency of wells and the field production facilities that was achieved through advanced computer analyses of massive amounts of Prudhoe field operating data BP has acquired since 1977, when the field began producing.

The result of this, Digert said, was an increase in Prudhoe¹s overall operating efficiency in 2017 reaching 85 percent, up from 83 percent in 2016. A two-percent increase in operating efficiency of the field translates to more oil being processed and shipped to the Trans Alaska Pipeline System because there is less “downtime” for wells and operating equipment.

For comparison, BP-operated platforms in the North Sea typically run at operating efficiencies in the mid-70-percentile range, Starck said. Field production facilities, mainly the large oil and gas processing plants, ran at 95 percent efficiency in 2017, on average.

One result of the increased amount of well work is a return to production of old wells that were taken off-line, said Starck. A dramatic example is at Flow Station 2, a process plant in the eastern side of the field, where the number of wells available for production was increased from 65 in 2015 to 90 in 2017.

The increase in the number of producing wells along with improved plant efficiency resulted in a production increase from about 20,000 barrels per day to more than 30,000 barrels per day through Flow Station 2, Starck said.

BP also increased production at the Lisburne production facility, which is also on the east side of the Prudhoe field, from 24,000 barrels per day in 2016 to 40,000 barrels per day in 2017, she said.

Digert said the overall effect has been to make 750 wells available for production in 2017, up from 650 in 2015. The additional 100 wells gives the field operators more flexibility in rotating among the wells to optimize output, he said.

For the new wells BP did drill, with the two rigs operating, the company was able to focus on pockets of oil bypassed earlier in the northern parts of Prudhoe as well as deep, undeveloped sections of the main producing reservoir, Digert said.

BP is also tapping natural gas liquids like condensate from gas produced from isolated parts of the reservoir. In the main parts of the reservoir the gas has been produced and reinjected for years, with liquids like propanes and butanes removed, so that the bulk of the gas in the field is now dry, or lean, gas. The natural gas liquids that have been extracted are either used in enhanced oil recovery to produce more crude oil or they are mixed, or blended, with the crude in trans-Alaska oil pipeline and shipped to market.

Tapping the “liquids rich,” gas can be rewarding, Digert said, with 15 to 20 barrels of liquids extracted per million cubic feet of natural compared with about 10 barrels extracted from the lean, or “dry” gas. The net result of this has been an addition of over 13,000 barrels per day of additional liquids production over the past two years, mostly as condensate.

Prudhoe Bay remains critical to all North Slope oil production because without it much less oil would be flowing through the oil pipeline, to the point that it might not be economically viable to operate.

The field was also the first, and biggest, of the North Slope fields discovered in the late 1960s and 1970s, and it became an economic “anchor” that made the Trans Alaska Pipeline System economically feasible to build.