Endicott field continues to deliver

Produced 2.9 million barrels of oil in 2012; BP continues with enhanced oil recovery program to slow production rate decline

Alan Bailey

Petroleum News

Since going into operation in the late 1980s and following peak production in the early 1990s, BP’s Endicott field continues to make a valuable if modest contribution to Alaska North Slope oil output. In 2012 the field delivered 2.9 million barrels of oil, according to a report submitted by BP in March to the Alaska Department of Natural Resources. Total cumulative production from the field since startup has been 461 million barrels of oil, the report said.

Operated from an artificial gravel island in the nearshore waters of the Beaufort Sea, connected by an artificial causeway to the North Slope mainland just east of Prudhoe Bay, the field is in the state’s Duck Island unit.

The field taps an oil pool in the Kekiktuk formation, a sandstone rock unit in what geologists refer to as the “Ellesmerian sequence,” the relatively old rock sequence that includes the reservoir rocks of the giant Prudhoe Bay oil field. The Kekiktuk sands are, however, older than the rocks of the Prudhoe Bay reservoir.

Recovery techniques

The water and natural gas are used in combination in a process known as “water-alternating-gas.” The water consists of seawater and water separated from oil during oil production, while gas used for oil recovery is produced from within the Duck Island unit.

BP’s pan of development says that the company is currently conducting engineering studies, to evaluate the potential for further improved Endicott oil production by the injection of water into the field’s gas cap, and by the use of a BP trademarked technique called “Brightwater,” in which chemical polymers placed in the water control the path of the water through subsurface rocks.

The plan also says that BP anticipates expanding its use of miscible injectant at Endicott, with the monitoring of injectant movement through the reservoir used to determine the timing and scope of additional injectant use.

A well workover program was initiated for the first quarter of this year, and the field owners continue to monitor field performance, with the possibility of future drilling in the field, the plan says.

In addition to the main Endicott oil pool, the Duck Island unit contains three other much smaller pools: the Eider participating area, the Sag Delta North participating area and the Minke tract.

The Eider participating area, with a reservoir in the Ivishak formation, the formation that forms the main reservoir in the Prudhoe Bay field, has been out of production for a number of years because of “uncompetitive” levels of water production — a test in June 2009 flowed fluids consisting of almost 100 percent water, the Duck Island unit report says. However, BP will continue with reservoir characterization work, seeking new ways to recover oil from the participating area, the report says.

The Sag Delta North participating area, also in the Ivishak formation, produced 98,365 barrels of oil in 2012, using water injection to maintain production. Total cumulative production from the participating area is 8.5 million barrels, the report says. BP will continue to evaluate the potential for further drilling in the participating area, or into surrounding drilling targets, the report says.

The Minke tract, the most recently developed of the Duck Island oil pools, produced 195,000 barrels of oil in 2012, using a single production well, with a cumulative production of 779,000 barrels since production started in April 2009. The reservoir is in the Sag River formation, equivalent to the topmost reservoir unit in the Prudhoe Bay field. No further drilling is currently planned for the tract, the report says.