Jon L. Konkler¹, Douglas S. Hastings¹, Debra H. McGimsey², Henry Posamentier³
(1) ARCO Alaska, Inc, Anchorage, AK
(2) BP-Amoco, Anchorage, AK
(3) ARCO Oil & Gas Co, Plano, TX

Abstract: Tabasco sands, North Slope, Alaska: an incised valley mapped with 3D seismic data

A shallow coarse clastic reservoir in the Kuparuk River Unit (KRU), North Slope of Alaska, has been delineated using 3D seismic and limited borehole data. The 'Tabasco Sands', an informally-named unit within the late Cretaceous Colville Group, comprises a shallower, secondary target to primary production from the Kuparuk River Formation, and constitutes “behind pipe reserves”. 3D seismic data and workstation interpretation tools, such as time and horizon slice techniques, have been combined with well log data to define reservoir limits and architecture.

Well data suggest that the Tabasco Sands are incised into underlying shales, have high lateral heterogeneity, and are limited in aerial extent. At Drill Site 2T (KRU), 3D seismic images suggest the presence of a large erosional feature, the 'Tabasco Valley', approximately 1/2 mile wide, 3 miles long, and up to 250 feet deep and oriented approximately normal to the shelf/slope break. The feature is interpreted to be an incised valley. The valley fill consists of nested channel complexes up to 100 feet thick filled with coarse-grained sand and conglomerate.

The valley is interpreted from anomalous geometries in cross-section and has a sinuous, channel-like map pattern. Mappable seismic geometries within Tabasco Valley are steeply dipping off-lapping reflections and flatter-lying onlapping reflections. The base of Tabasco valley is erosional, indicated by sharp truncation of underlying clinoforms. The off-lapping features within the valley are associated with medium to coarse-grained lithic sandstone and conglomerate. The flatter onlapping events are associated with thin-bedded, fine-grained sand, silt and mud.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana