A Giant Looming in the Mist: The Sag River Reservoir from Prudhoe Bay Field, Alaska, USA

James Copen, Sandra Phillips, Jon Konkler, and Peter Harrison
BP, Anchorage, AK

This paper will address the challenges of developing and revitalizing a giant “tight sand” oil and gas reservoir which has for decades been overshadowed by the super-giant immediately below. It is not commonly appreciated that there are, in fact, two giant reservoirs at Prudhoe Bay Field on Alaska’s North Slope. With over 11 billion barrels of oil produced to date, the Permo-Triassic Ivishak Formation is justifiably recognized as the primary reservoir at Prudhoe. However, lying just 30 to 50 meters above, the late Triassic to early Jurassic Sag River Sandstone contains over 1.5 BBOIP at Prudhoe Bay alone, with additional undeveloped potential elsewhere on the “slope”. Estimated recovery from the Ivishak is expected to exceed 60%. In stark contrast, recovery from the Sag River has barely scratched 10%. This paper will describe the reasons, geologic, technical and economic, behind this disparity and present an overview of proposed plans to rectify it. We will characterize the new perspective with which the Sag River is being approached and describe new or untested technologies being considered to unlock resources which “conventional wisdom” suggests are inaccessible. These cover a wide spectrum from reservoir description, seismic interpretation, rock properties modeling, 4D seismic and petrophysical modeling, to geocellular modeling and reservoir simulation, drilling and completions, and reservoir stimulation. Some are quite innovative. The goal of this paper is to describe these and other efforts aimed at dramatically improving recoverability of hundreds of millions of barrels of oil “locked up” in the technically challenging Sag River Sandstone on Alaska’s North Slope.

AAPG International Conference and Exhibition, Cape Town, South Africa 2008 © AAPG Search and Discovery