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New drill site possible for northeast West Sak Work continues at four Kuparuk River unit satellites, with exploration possible for some in-field areas, new acreage south of Tarn Kristen Nelson Petroleum News
There are four satellites in production at the Kuparuk River unit on Alaska’s North Slope: West Sak, Tarn, Tabasco and Meltwater.
West Sak, with the highest current production rate, also has the greatest potential for additional development as the shallow viscous oil reservoir overlays much of the deeper Kuparuk reservoir from the boundary of the Milne Point unit on the north to the southern boundary of Kuparuk.
West Sak averaged 18,116 barrels per day last year with production from drill sites 1B, 1C, 1D, 1E and 1J, Kuparuk River field operator ConocoPhillips Alaska told the state in late June. Cumulative production through the end of 2006 was 25.7 million barrels. Active wells include 36 producers (11 conventional, 22 multilateral and three single horizontal wells) and 35 water injectors (22 conventional, two undulating horizontal, one single horizontal and 10 multilateral horizontal wells).
ConocoPhillips said West Sak well completions “continue to evolve from the initial vertical wells and horizontal wells with sand control to horizontal wells with slotted liners.” West Sak wells average 500 barrels per day including the new multilaterals at drill site 1J. The highest production rate is 2,166 bpd from the 1J-152 multilateral, with 7,700-foot horizontal laterals in the D and B sands and a 3,500-foot lateral in the A sand.
Drilling has been in the core West Sak area in the south and is expected to move to the northeast West Sak area in 2008, the company told the Alaska Department of Natural Resources’ Division of Oil and Gas in 2007-08 plans of development for the satellite participating areas submitted in late June (see July 15 issue of Petroleum News for story on the Kuparuk main field plan of development).
The first West Sak plan of development was filed in 1997 and drilling began in 2000 and 2001 from drill sites 1D and 1C; moved to drill site 1E in 2004; and to 1J in 2006.
“Future drilling will be based on West Sak performance,” the company said, with the pace of proposed drilling in the plan (13 penetrations this year; eight to 10 in 2008; zero to two in 2009; 12-14 in 2010; and 25-27 in 2011) reflecting what the company called “one potential outcome.”
ConocoPhillips said 2007 West Sak drilling is planned from drill site 1J; 2008 drilling from drill sites 1J and 3K and others; 2009 drilling from existing drill sites; and 2010-11 drilling from both existing drill sites and from a potential new drill site.
Northeast West Sak development Drill site 1J development drilling began in 2006 and ConocoPhillips said the two-rig 1J program continued through 2006 and is planned to conclude in the first quarter of 2008.
The plan for development of the northeast West Sak area, or NEWS, north and northwest of the core area, includes drilling from existing drill sites and the potential development of one to two new drill sites.
Results of the NEWS appraisal drilling program done in 2005-06 and additional NEWS delineation drilling done at the end of the 2006 winter drilling season are being used to optimize future NEWS development plans.
ConocoPhillips drilled five successful NEWS appraisal wells in 2005-06, one each at drill sites 1Q and 3J and three from an ice pad north of drill site 1H.
Waterflooding main recovery mechanism Waterflood with produced water from Central Processing Facility 1 “for pressure maintenance and sweep continues to be the main recovery mechanism in the West Sak oil pool,” ConocoPhillips said.
Waterflood performance has been good in the majority of areas although there have been rapid breakthrough events, the company said, where “highly conductive” pathways were created between an injector and a producer. Two breakthrough events occurred in 2006.
The company said a study of the breakthroughs is ongoing; some early recommendations to mitigate future breakthroughs have been implemented “and the pace of these events has dropped off significantly.”
The newest West Sak development area, at the 1J drill site, has not had any breakthrough events. ConocoPhillips said it is developing a remediation strategy for wells that have experienced rapid breakthrough. One remediation treatment tried in 2006 was unsuccessful and the company said further strategies and technologies are being evaluated.
Expansion area 4 drilling requirements satisfied DNR granted a 60-day extension for drilling commitments for Area 4 in the eighth Kuparuk River unit expansion decision. ConocoPhillips said it met the drilling commitments with two wells drilled in the expansion area in 2006.
In April ConocoPhillips filed an application with DNR to expand the West Sak participating area; lands not included in the second West Sak participating area expansion application will contract out of the unit in accordance with the eighth KRU expansion decision requirements for expansion area 4 effective June 1.
Exploration possibility south of Tarn ConocoPhillips said exploration is possible south of the Tarn satellite, as is Cairn-interval appraisal at the field.
Tarn, at the southwest corner of the Kuparuk River unit, averaged 17,129 bpd in 2006 from 45 wells (28 producers and 17 miscible-water-alternating-gas injectors) at two drill sites, 2L and 2N, with cumulative production through the end of 2006 of 80.2 million barrels. This satellite accumulation, discovered in 1997, came online in 1998; development began in 1997 and continued into 2001, ConocoPhillips said.
Two new wells were drilled last year and the company said 2L-311 and 2L-309 “have been highly successful in demonstrating the potential of the eastern flanks of the field.”
ConocoPhillips said it continues work on an infill and peripheral drilling project with eight to 22 potential locations, with reservoir simulation studies under way on benefits of continued infill drilling and development of peripheral areas of both the 2N and 2L drill sites. The company said target areas are predominantly “thinner distal lobes that previously were assessed to be uneconomic.”
The company purchased six leases adjacent to and south of Tarn and is evaluating exploration potential.
ConocoPhillips said the Cairn interval may be appraised from Tarn “within the next several years,” with a preliminary play to perform a Cairn extended well test as part of a Bermuda development well this year. “Other appraisal plans for the area include testing a Bermuda equivalent amplitude anomaly to the south of the 2N reservoir and evaluation of deeper Tarn (C30) Albian sands within the pool.”
Tabasco expansion studied Tabasco is currently produced from a single pad, 2T, midway down the western side of the Kuparuk River field, with an average production rate of 3,900 bpd in 2006 and cumulative production through the end of 2006 of 12.8 million barrels of oil. Twelve dedicated wells at drill site 2T include 10 producers and two injectors.
ConocoPhillips said 10 wells were originally planned, but only nine were initially drilled due to waterflood behavior.
In 2003, however, a horizontal production well drilled at the top of the structure had performance sufficient to justify two more horizontal production wells, one each in late 2005 and early 2006. These horizontal wells on the periphery near the top of the interval “minimize water production without restricting production to uneconomic levels.”
“Performance data from the three existing horizontal wells will be used to determine the best completion strategy for future development wells,” the company said.
Future Tabasco facilities at drill site 2T include water injection expansion. ConocoPhillips said the new 10-inch water injection line to 2T “will provide sufficient water capacity for Tabasco expansion and the Kuparuk reservoir.”
The company said Tabasco development beyond 2T would have to be justified based on performance of the currently developed pool and results of ongoing Tabasco trend geologic and geophysical interpretation.
Based on work completed to date, a Tabasco oil quality test at drill site 3H to the north is likely within five years. “If commercially viable, a multi-well development of the Tabasco interval at DS3H is possible, however long-term performance of the horizontal production wells and optimization of the drive mechanism within Tabasco reservoir is needed prior to deciding on this development.”
Appraisal drilling at drill site 3H would be considered exploratory because of “the unproven status of the Tabasco horizon” under that drill site.
Meltwater; Cairn exploration possible Meltwater, some nine miles south of Tarn off the southwestern edge of the Kuparuk River field, was discovered in 2000. Production in 2006 averaged 2,946 bpd (from 12 production wells and seven miscible-water-alternating-gas injection wells) with cumulative production through the end of the year of 11.1 million barrels.
ConocoPhillips said that initially recoverable reserves were estimated at 52 million barrels but after development drilling began and the prospect was remapped in 2002, recoverable reserves were estimated at 31 million barrels.
Phase II development, in 2003 and 2004, “suggests that the Meltwater sand bodies are highly discontinuous with structural barriers that limit fluid movement through the reservoir,” the company said, and the recoverable base is now believed to be only some 20 million barrels.
No further development drilling is planned for 2007-08. “Pending outcome of the field surveys and rebuild of the full field model, it is expected that a recovery plan will be established that may require additional new wells or sidetracks of existing wells. Horizontal or undulating wells will be considered,” the company said.
The Cairn interval near DS 2P was drilled in 2002 and found to be gas bearing and work is under way “to define a potential Cairn exploration well and test the gas potential of the interval.”
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