Reservoir Description of the Tarn Sand System, North Slope, Alaska, by Integration of Seismic Architecture and Turbidite Depositional Elements

By

D.S. Hastings, W.R. Morris, M.J. Faust, and K.J. Helmold (Phillips Alaska, Inc.)

The Tarn Field was discovered in 1991 but languished until a 3D seismic survey was acquired which revealed the size and complexity of the Tarn turbidite system. Four successful delineation wells were drilled in 1997 and Tarn Field produced first oil 16 months later. Tarn currently produces about 27,000 BOPD from two separate features. Seismic-scale architecture, interpreted with Advanced Seismic Interpretation techniques, has been integrated with well logs and core to produce a detailed reservoir description. The two Tarn Sand complexes show contrasting architectures. The southern complex is dominantly aggradational, with a back-stepping geometry, enhanced by syndepositional faulting. In contrast, deposition in the northern sand complex is progradational, and deposition is by lateral compensation.

The Tarn Sands represent confined and unconfined slope-apron systems and, to a lesser extent, levee-channels. Sediment supplied to these systems evolved through time from mud-rich to mixed sediment and sand-rich sources. Reservoir distribution and characteristics are closely correlated to depositional elements and sedimentary facies within these systems. The sand-rich systems have the best reservoir quality and connectivity. In mixed sediment systems, reservoir quality decreases from channel to levee deposits. Slope aprons con- fined in a sub-basin show greater reservoir connectivity than in unconfined settings.

Integration of seismic architecture with turbidite elements has enabled successful development drilling, prediction of well results and a detailed and robust reservoir description.

AAPG Search and Discovery Article #90008©2002 AAPG Pacific Section/SPE Western Region Joint Conference of Geoscientists and Petroleum Engineers, Anchorage, Alaska, May 18–23, 2002.