The Alaska Oil and Gas Commission conducted a public hearing on March 14 to review ConocoPhillips’ application to modify the Alpine Oil Pool in the Colville River unit. Drilling from the CD5 pad in the National Petroleum Reserve-Alaska has revealed the westward extension of the Nanuq Kuparuk reservoir in the unit and the company wants to begin development of the oil pool in the reservoir to the west of the pool’s current boundary.
The Alpine Oil Pool involves oil trapped in the Alpine and Kuparuk sands in the Beaufortian sequence, one of the major North Slope petroleum bearing rock sequences.
The pool modifications would involve the addition of six land sections on the west side of the current pool boundary and the removal of 16 full and partial sections from the pool’s eastern side.
Drilling results
ConocoPhillips geologist Doug Knock told the commissioners that his company had drilled the CD5-313 pilot hole in 2015, sidetracking a 7,400-foot production lateral from that well. West of that well the company drilled the CD5-315 pilot hole, sidetracking a 10,000-foot lateral from that well. These laterals extended through continuous Kuparuk C oil reservoir sands, about eight feet thick. Knock said that the CD5-315 well had encountered a thickness of seven to 12 feet of continuous sand with very good reservoir quality: The estimated permeability is well over 100 millidarcies.
Based on these promising drilling results, ConocoPhillips wants to continue drilling to the west, with plans to drill the CD5-314X and CD5-316 wells by the end of this year. But the second of these wells, an injection well, would penetrate reservoir rocks outside the western limit of the current Alpine Oil Pool, hence the application for a pool expansion to the west.
During a confidential section of the hearing Knock presented to the commissioners evidence from seismic data and geological analysis that the Kuparuk Nanuq oil pool does extend beyond the current Alpine Oil Pool boundary.
Change to orders
For the Alpine pool ConocoPhillips has also requested the removal of a conservation order, the introduction of a new injection order, and a change to an existing injection order.
The conservation order relates to subsurface safety valves for producing wells and gas injection wells. ConocoPhillips says the existing conservation order is superfluous to requirements, having been superseded by a more recent order that applies to all western North Slope fields.
The proposed injection order would place a pressure limit of 0.81 pounds per square inch per foot for fluids injected into injection wells, a pressure limit high enough to allow effective fluid injection into field reservoirs but not high enough to damage shale units above the reservoirs. ConocoPhillips petroleum engineer Anu Sood described modeling that showed fluids being contained in subsurface Alpine and Kuparuk reservoir sands at that 0.81 level of injection pressure.
The amended area injection order for the Alpine Oil Pool specifies all of the various fluids that ConocoPhillips may inject into the pool reservoirs, in particular for pressure management. The primary injectants would be water from the Kuparuk seawater treatment plant, produced water from the Alpine Central Facility, and miscible injectant, also from the Alpine Central Facility, Sood explained. Miscible injectant consists of a mixture of natural gas and natural gas liquids. Seven other fluids of various types may be used in much smaller volumes.
Formed in 1998
The Alpine Oil Pool, encapsulating oil in the Alpine sands, was originally formed in 1998. It was expanded west in 2004. And, in 2009, following the discovery of pressure communication between the Alpine and Nanuq Kuparuk reservoirs, a Kuparuk pool was combined with the Alpine pool to form a single pool.
Recent horizontal drilling from ConocoPhillips’ new CD5 pad, the first production pad in the National Petroleum Reserve-Alaska, has proved particularly successful. In late 2015 the pad was producing oil at rate of about 20,000 barrels per day using a combination of injection and production horizontal wells. Production from CD5 is processed through the Alpine Production Facilities.
