Forest Oil Corp. has received permission to begin a waterflood pilot at its Redoubt Shoal field in Cook Inlet.
On Aug. 26 the Alaska Oil and Gas Conservation Commission authorized a test to evaluate water injection for enhanced oil recovery from the Hemlock formation through Sept. 30, 2007, unless Forest applies to extend the test, expand the pilot area or abandon the pilot.
Forest told the commission that without waterflood recovery of oil would be about 6 percent of original oil in place or about 3 million barrels without any pressure maintenance process. At full field development, the company estimates that waterflood might increase recovery to more than 20 percent. The pilot project will provide data on recovery benefits.
Injection fluid for the waterflood pilot will be filtered, produced Hemlock formation water from Redoubt Shoal unit wells 1, 2, 5A and 7, with an initial injection rate of 2,500 to 3,000 barrels of water per day. Forest told the commission it anticipates injection will exceed withdrawals from the area offsetting the injector, with pressure support anticipated at the 1 and 7 wells, and possibly also at the 2 well.
The injection pumps will be at Forest’s onshore Kustatan production facility.
There are five production wells in the Hemlock formation at the Redoubt Shoal field and waterflood will be through a single injector, Redoubt well 6, an oil producer with cumulative production of 177,497 barrels of oil through May 2004.
A pilot project lasting about 36 months is planned.
Forest told the Alaska Division of Oil and Gas in its fourth plan of development for Redoubt that it expects the pilot waterflood project will begin during the fourth quarter of 2004.
No further drilling planned
Forest also said in its plan of development that no additional wells to the Hemlock oil formation are planned from August 2004 through August 2005, the period covered by the plan. Only one well, the Redoubt Unit No. 7, was completed during the third plan of development; the drilling rig was then demobilized from the Osprey platform.
During the third plan of development (August 2003 to August 2004), “… a comprehensive field study was undertaken to try to explain the production thus far from the Redoubt Unit,” Forest said. Much of that information will be used in preparation of an application for an areawide injection order. “Water injection/pressure maintenance is projected to begin by 2005,” the company said.
Also during the 2003-04 plan, the Gas Technology Institute “continued its study, with some data provided by Forest, to determine if there are any seismic attributes that will allow for discrimination between coals and gas-charged sands in the shallow Tertiary sediments. Results of the study to date are inconclusive,” Forest said.
During the 2004-2005 plan period Forest said it “plans to conduct studies regarding an anticipated waterflood of the Hemlock oil reservoir.” After evaluation of results of the pilot waterflood just approved by the commission, Forest said it will consider “additional drilling to further delineate the field and/or initiation of a full field waterflood.”
There will be minor modifications necessary to facilities for the pilot waterflood and Forest said it will look at West McArthur River unit produced water and Cook Inlet seawater, in addition to Redoubt produced water, as sources for waterflood.
Gas participating area approved
Forest has also received approval from the Alaska Division of Oil and Gas for a gas participating area at Redoubt. An extended gas production test from the Redoubt No. 3 well began in May 2003, and Forest told the division it currently plans no additional gas wells.
The company said the No. 3 well, the only well completed in the G-0 gas sand in the Tyonek formation, will continue to produce gas reserves from that sand until they are depleted. “The data gathered to date would suggest that this one well completed in the G-0 sand is sufficient to produce all potential G-0 reserves identified,” the company said.
All of the gas produced is expected to be used as fuel gas at the Kustatan production facility in support of Redoubt unit operations, although the gas was also to be used in a test of gas lift production from the Redoubt Shoal Hemlock oil producing formation, which underlies the gas-producing Tyonek formation. Forest said that after the test, gas would again be sent to the separator at Kustatan and then consumed by the Kustatan turbine generators to produce power to operate both Kustatan and the Osprey platform at Redoubt Shoal.
The No. 3 well was originally drilled as an oil well in 2001, and the G-0 sand was tested in October 2001. The 40-foot thick sand is at a depth of 11,321 to 11,361 feet true vertical depth, and flowed gas at a maximum rate of 8.67 million cubic feet per day. In May 2003, the No. 3 well was re-completed in the G-0 sand as a gas well, and testing began that month.
Forest said that based on data from July 2003 and September-November 2003, fuel use is 3-4 million cubic feet per day.
Commercial production of Redoubt Shoal oil began Dec. 9, 2002, and the field qualifies for a 5 percent royalty for the first 25 million barrels of oil and the first 35 billion cubic feet of gas. Forest is 100 percent working interest owner at Redoubt. There are more than 90 overriding royalty interests and Unocal has a 1 percent overriding royalty interest which kicks in after cumulative gross sales equal 40 million barrels. As of July, commission records show cumulative oil production from Redoubt of almost 1.4 million barrels of oil, 1.3 million barrels of water and 318 million cubic feet of gas. For the month of July production from Redoubt was 39,070 barrels of oil, 25,267 barrels of water and 9.572 million cubic feet of gas.
