The transition to gas at Prudhoe Bay

BP is currently working with the Alaska Oil and Gas Commission to evaluate natural gas offtake rates from the Prudhoe Bay field, in the event that the field starts to export gas though a future North Slope gas line, Mike Utsler, BP senior vice president for greater Prudhoe Bay, told Petroleum News June 9. At issue is the question of minimizing the impact of gas production on oil recovery from the field he said.

Re-injected gas is used to maintain the pressure in the Prudhoe Bay reservoir.

“The minute you take gas out of the reservoir you will be taking pressure out of the reservoir and, therefore, you will be accelerating the decline of light oil production, and viscous oil production potentially,” Utsler said.

It would be possible to partially offset the pressure decline by injecting carbon dioxide extracted from the produced gas in the gas treatment plant at the upstream end of the gas line, and by expanding water injection in the field.

However, these approaches would not fully compensate for the drop in gas injection, leaving the possibility of some otherwise recoverable oil remaining stranded in the reservoir. Enhanced oil recovery techniques might be used to tease this stranded oil from the ground, but BP also sees a program of accelerated drilling over the next 10 years, prior to the start of gas sales, as a potential means of maximizing ultimate oil recovery.

BP is using a sophisticated computer model of the Prudhoe Bay field, encapsulating data from 2,500 well penetrations and well core data from across the field, to analyze various oil and gas production scenarios, by testing how the field would respond to different fluid movements and pressure changes, Utsler said.

“We have built what is recognized as one of the world’s most sophisticated what are called full-field reservoir models,” he said.

—Alan Bailey