Unique Horizontal Wells Boost Primary and EOR Production, Prudhoe Bay Field, Alaska

TYE, ROBERT, ARCO Technical & Operational Services, Plano, TX; BECKY WATSON, ARCO Alaska, Inc, Anchorage, AK; PATRICK MCGUIRE, ARCO Alaska, Inc., Anchorage, AK; MATHEW MAGUIRE, ARCO Alaska, Inc, Anchorage, AK

Using horizontal-wells, and an unprecedented enhanced-oil recovery (EOR) process, ARCO is capitalizing on geologic, and fluid-distribution complexities in the Triassic Ivishak Sandstone, to recover untapped or bypassed reserves. Millions of barrels of reserves reside in a basal, 100-foot thick succession of en echelon, offlapping deltaic wedges. Distributary-mouth bar and distributary-channel sandstones are targeted. Onlapping, retrogradational mudstones form laterally extensive flow barriers, impeding the gravity-drainage process.

Reservoirs are structurally isolated in fault blocks covering 100 acres or less. Reserves are sacrificed with conventional wells, due to small drainage areas. However, a horizontal well with a 90° bend, or fishhook shape, maximizes exposure to productive sandstones. First stable production was 3750 BOPD and 2600 GOR. Production was 1.2 MMBbls as of 4/97.

Horizontal wells in a Miscible Injectant Stimulation Treatment (MIST) program recover millions of barrels of EOR oil. In a lateral MIST project, a horizontal well is drilled from an existing well in a watered-out pattern. Maximum-sweep efficiency is achieved keeping the wellbore near the reservoir base as it arcs between an injector and outlying producers. Miscible injectant is introduced at the well tip, forming a gas bulb pushing oil to the producers. After adequate injection, the perforations are squeezed and the well is re-perforated nearer its heel. By sequentially injecting gas, squeezing perforations, and re-perforating in a more proximal position, post-waterflood oil is stripped from the reservoir. Incremental EOR from three horizontal wells exceeds 1.3 MMSTB. Simulations predict incremental EOR of greater than a million barrels per horizontal well.

AAPG Search and Discovery Article #90911©2000 AAPG Pacific Section and Western Region Society of Petroleum Engineers, Long Beach, California