John A Howell¹, Simon Knight², David Keighley³, Kevin Keogh¹, David Hodgetts¹, John Kavangh¹

(1) Univerisity of Liverpool, Liverpool, United Kingdom
(2) Norsk Hydro, Norway
(3) St Mary's University, Halifax, NS

ABSTRACT: Reservoir Modelling of Complex Estuarine Incised Valley Fills: An Example from the Book Cliffs of Eastern Utah

Estuarine incised valleys, cut during falling sea level and modified and filled during subsequent sea-level rise are typical considered to be good hydrocarbon reservoirs. An incised valley from the Cretaceous Blackhawk Formation from the Book Cliffs in Eastern Utah was studied in terms of its facies development, sequence stratigraphy and potential reservoir behaviour.

The incised valley is up to 3.5 km wide and 25 metres deep. Mapping of valley margins has revealed a complex system, comprising three tributaries that coalesce in the study area. The valley system was cut through a large coal mire and into wave dominated shallow marine shoreface deposits. The valley is filled with fluvial sandstones (at the base), meandering tidal heteroliths, tidal flats, subtidal bars, coals and shell beds.

Detailed mapping and logging of 70 measured sections provided the data to build a 3D reservoir style model in IRAP RMS. The model highlights the complex three-dimensional distribution of facies within the valley and the relationship with the surrounding shoreface parasequences. Additional smaller models were built to capture the effective fluid flow properties of the IHS and tidal flat deposits. Once built, the main model was upscaled and simulated in Eclipse using a 22 layer simulation. Results show that the fluvial base to the valley system is a high permeability pathway in which water breakthrough occurs very early. The rest of the valley is effectively a flow barrier which partitions the shoreface reservoir and will potentially trap attic oil in juxtaposed good reservoir upper shoreface sandstones.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado