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AOGCC approves West Sak pool expansion Adds 200 feet of Schrader Bluff sands above the existing pool and allows the use of VRWAG technique for enhanced oil recovery By Alan Bailey Petroleum News
The Alaska Oil and Gas Conservation Commission has approved an expansion to the West Sak oil pool in the Kuparuk River unit. The commission has also approved the use of a technique called viscosity reducing water alternating gas, or VRWAG, for producing oil from the pool.
ConocoPhillips, operator of the unit, had requested the unit expansion primarily to enable the development of additional oil in the West Sak by bringing the vertical extent of the pool into line with equivalent oil-bearing rocks in what is referred to as the Schrader Bluff formation in adjacent oil and gas units. The expansion also involves some horizontal adjustments to the extent of the oil pool, to bring the pool boundary into line with the current unit boundary.
Specialized techniques West Sak and Schrader Bluff contain thick, viscous oil and lie at relatively shallow levels above the deeper reservoir rocks of the traditional oil fields of the North Slope. Teasing the thick oil out of the sandstone reservoirs has required specialized techniques, including the use of high-tech horizontal drilling.
Since 2009 ConocoPhillips has been conducting a large-scale pilot program to test the use of VRWAG techniques in the West Sak viscous oil pool. And, having achieved success with that pilot, the company asked the commission for approval for full-scale use of the technique. The technique involves flushing of oil from the reservoir, alternately using water and a mixture of gas and gas liquids. The gas mixture causes the oil to swell and hence become less viscous - ConocoPhillips says that VRWAG could increase viscous oil recovery by 5.2 percent of original oil in place.
200-foot expansion The rock formation called West Sak in the Kuparuk River unit is equivalent to what is referred to as the Schrader Bluff O sands in adjacent units. The vertical expansion of the viscous oil pool at Kuparuk involves adding the Schrader Bluff N sands, a sequence of rocks about 200 feet thick, equivalent to similar N sands in the other units and lying directly above the West Sak. ConocoPhillips told the commission that the main oil bearing sand unit in the N sands at Kuparuk may contain 320 million barrels of oil.
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