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BP begins water flood at Sag River oil pool at Milne Point Production from deepest reservoir at field has been problematic — water flood will be tried in one block; lean gas, miscible injectant may be evaluated; company estimates water flood recovery of up to 45 percent Kristen Nelson PNA Editor-in-Chief
BP Exploration (Alaska) Inc. is beginning water flood in the Sag River oil pool at Milne Point, a process which could recover several million barrels of light oil from the Sag River formation underlying the main Kuparuk River producing formation at Milne Point.
On April 23 the Alaska Oil and Gas Conservation Commission authorized injection of fluids for enhanced oil recovery in the Sag River oil pool.
The Kuparuk River formation, about 7,500 feet subsurface, is the major producer at Milne Point. Field operator BP also produces from the shallow, viscous Schrader Bluff formation at about 4,000 feet subsurface. The Sag River formation, at about 8,700 feet subsurface, is the deepest of the producing formations at Milne Point.
BP has enhanced oil recovery operations under way for the Kuparuk River and Schrader Bluff oil pools at Milne and in December the commission authorized use of non-hazardous treated wastewater from the Milne Point wastewater treatment plant and non-hazardous water collected from Milne Point reserve pits, well house cellars and standing ponds for enhanced oil recovery in those pools. Kuparuk River EOR uses miscible gas injectant, including natural gas liquids imported from Prudhoe Bay.
Sag River production began in 1995, and through Jan. 21 of this year, 1.3 million barrels had been produced, with electric submersible pump artificial lift problems and high decline rates making development problematic. Sag River economics tested BP has divided the Sag River into four zones, only one of which contains reservoir quality rock. Net pay ranges from nine to 18 feet in the zone. The commission said the structure of interest is a narrow anticline that trends northwest through the center of the unit, broken up by faults into a series of small compartments.
BP has completed conventional producers in the Sag River pool with electrical submersible pumps to test economic and development potential, but the wells didn’t produce for long because of high gas-oil ratios and poor pump performance. All but three of the Sag River wells were re-completed to the Kuparuk River formation or were suspended or abandoned.
In 2001, BP horizontally sidetracked two wells with coiled tubing and completed them with jet pumps for artificial lift, with favorable productivity and jet pump performance.
The commission said BP is proposing water injection from one of the wells to provide pressure support for the other.
“Without water injection, reservoir pressure and production rate will decline,” the commission said. BP also requested miscible and lean gas injection.
BP has told the commission that if they are successful in stabilizing water flood support between the two wells, additional fault blocks near C pad may be developed.
Water for injection will be source water from dedicated wells on the F and K pads and produced water from the Milne Point central processing plant. MI subject to economics The commission said if water flood is successful in providing pressure support, BP may test lean gas injection and even miscible gas injection.
If BP finds injection of miscible gas into the Sag River formation economically competitive with miscible injection into the Kuparuk River formation, the MI would be a blend of produced gas from Milne Point and natural gas liquids from Prudhoe Bay.
Water injection will begin in one fault block to test secondary recovery. Estimated original oil in place in the block ranges from 4.0 to 7.4 million barrels in place. BP estimates primary recovery of 15-18 percent and water flood recovery of up to 45 percent.
The commission said BP is reevaluating original oil in place in the Sag River formation, but estimates in 1998 were about 62 million barrels in three areas: 9.7 million in the F pad area; 49.1 million in the central area (E and C pads) and 2.9 million in the K pad area.
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