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The Explorers 2019: BP re-exploring Prudhoe Bay
New high density broadband seismic data acquisition and analysis to locate, exploit remaining oil pockets
Steve Sutherlin for Petroleum News
BP Exploration Alaska is setting the stage to comb the Greater Prudhoe Bay area for smaller oil pools it can target with advanced drilling techniques over the next decade or so, with an eye on adding new production in the 42-year-old field.
The key to the effort is a massive 3-D seismic survey Prudhoe operator BP describes as “high density broadband seismic,” which will be acquired in the first half of 2019. The 455-square-mile seismic shoot will cover the majority of the Greater Prudhoe Bay area.
“That’s the largest that we’ve ever done at Prudhoe Bay and we’re using state-of-the-art technology, so we’ll have the best image that we’ve ever had,” Janet Weiss, president of BP Exploration Alaska said on Jan. 18, 2019.
The company has two drilling rigs active at Prudhoe Bay.
“We’ve restarted those rigs, getting our well locations identified, so that we have many, many more years of drilling in Prudhoe,” Weiss said.
The new data - when combined with North Prudhoe seismic BP acquired in 2015 - will “provide a single continuous seismic image” across the unit, allowing for more efficient drilling. The company said this technology “enables denser and larger datasets to be acquired when compared to legacy methods.”
Technology key As the Prudhoe Bay field matures, the use of modern technology has become critical to extending field life and to maintaining the field’s economic viability, Fabian Wirnkar, BP vice president for reservoir development, said Oct. 5, 2018.
Locating and exploiting the remaining small pockets of oil in the field requires state-of-the-art technology in the form of data acquisition, storage and analysis, and in the form of sophisticated drilling techniques.
Modern seismic surveying, produces crisp images of faults and other subsurface features, enabling the location of features where additional oil may be found. Multilateral wells, drilled out from single wells connecting to the surface, can thread though those remaining pockets of oil. At the same time, the seismic imaging can enable, for example, the precise injection of water into areas where it can be most effectively used.
2019 development drilling The new upgraded seismic information will guide BP to more efficient development drilling in 2019 at Prudhoe Bay, the company said in its annual progress report for the initial participating area, or IPA, of the field covering the 2018 calendar year, and its plan of development for work from July 1, 2019, through June 30, 2020.
The new data will “underpin the reservoir management and development programs,” BP said.
There remains an important role for development drilling among more than 1,400 existing wells at the field, BP said, adding that drilling “will continue at a pace consistent with the business environment and the ability to identify viable targets informed by ongoing surveillance, supplemented by new seismic data being acquired in the first half of 2019.”
Production in 2019 “will largely be driven through continuing improvements in operating efficiency, optimizing base production and wellwork,” the company said. Some 400 rate adding jobs and some 550 non-rate adding jobs are planned.
IPA rotary penetrations are expected to be about the same as in 2018, between five and seven. Coil penetrations, however, will be increased from 10 in 2018 to 15-23 in 2019, with rig workovers expected to increase from two in 2018 to from two to eight in 2019.
BP said wellwork activity “remained at a high level in 2018 with 360 rate adding jobs done and about 900 total jobs performed.”
In 2018 a coil rig and a rotary rig drilled 15 wells. There was a pause in drilling mid-year allowing BP to pursue cost and efficiency gains and evaluate future targets for drilling. “The coil and rotary rigs were brought back in service in December,” BP said, with future drilling opportunities to “be identified by ongoing surveillance and utilizing the new seismic being acquired and processed in 2019-2020.”
“As the IPA enters its 42nd year online, 31 years beyond the end of the field’s production plateau, the PBU owners’ key priority is efficient production of the existing wells and facilities,” the company said. “Minimizing natural decline is the constant goal.”
BP is transitioning to the use of what is termed “predictive maintenance analytics,” a data intensive technology that enables the prediction of equipment failures before failures happen. This approach improves efficiency by increasing equipment up time, Wirnkar said.
Exceeded expectations When Prudhoe Bay went into production in 1977, the initial estimated ultimate recovery was 9.6 billion barrels of oil. To date, however, the field has generated more than 13 billion barrels of oil, making it the most productive field in U.S. history. According to BP, a bit more than 1 billion barrels of producible oil remain in the field.
At first, the field reservoir pressure was high and there was a 600-foot oil column; production over the years has lowered the pressure, while the remaining oil in place has fragmented into a series of relatively small pockets, Wirnkar said. Waterflood and gas injection have been used to sustain the reservoir pressure to levels where oil production can continue.
Currently BP recycles about 8 billion cubic feet of gas per day through the field reservoir - without that gas recycling and injection, the field would no longer produce any oil, Wirnkar said.
Continued operation depends on efficiently, economically and safely developing the resources that are known to exist, while also seeking new opportunities for growth, he said.
“There is still a lot that we can do here,” Wirnkar said.
Recovery discovery In addition to infield exploration, BP is seeking to capitalize on known but difficult to produce reserves in the IPA by developing creative production techniques based on data analysis and advanced production technology.
The company obtained Alaska Oil and Gas Conservation Commission approval in late 2018 to allow for commingled downhole production for wells completed in both the Prudhoe oil pool and the Put River oil pool which overlies the Prudhoe oil pool. The ruling allows production of some 6.9 million barrels of oil in place in Put River, which would otherwise be stranded.
Put River consists of three lobes - Central, Southern and Western - of the Put River sandstone, with a fourth lobe, the Northern, in hydraulic communication with the Prudhoe oil pool and included as part of the Prudhoe pool. The Southern lobe of Put River has had production since 1999 with an active waterflood.
Oil and gas condensate was identified through 2005 appraisal activities in the Western and Central lobes respectively, the commission said, “but further development was not pursued at that time in part due to low flowrates that resulted in operational challenges associated with hydrate deposition.”
The Central lobe contains an estimated 1.1 million to 2.7 million barrels of oil in place and the Western lobe contains an estimated 69.6 billion to 104.4 billion cubic feet in place with a condensate yield of approximately 40 barrels per million cubic feet, with a condensate in place value of between 2.8 million and 4.2 million barrels of oil.
The commission said several wells penetrating the Prudhoe and Put River oil pools would be candidates for downhole commingling, which “should allow for increased flowrates and flow velocity in the tubing and reduce the potential for the hydrate deposition that is problematic in production from wells completed solely in the (Put River oil pool). Since standalone production of the Central and Western Lobes is not viable due to hydrate deposition those reserves are essentially trapped. Commingling of production with the (Prudhoe oil pool) will allow these resources to be recovered.”
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