Application of Parasequence Stratigraphy to Reservoir Modeling
O'BYRNE, CIARAN, and STEPHEN FLINT, University of Liverpool, Liverpool, United Kingdom
The Cretaceous Blackhawk Formation (Mesaverde Group), exposed in the Book Cliffs of southeast Utah, comprises a set of progradational, aggradational, and rare retrogradatioanl clastic parasequences dominated by shoreface sand bodies. Such sand bodies form important hydrocarbon reservoirs in the Gulf Coast, the North Sea, and other oil provinces worldwide.
The 40-50-m-thick Grassy Member shoreface system comprises three forewardstepping parasequences. Individual parasequences exhibit a systematic distribution of lithofacies and major changes in vertical log profile relative to depositional dip. Parasequence stacking can result in repetition of certain facies associations in vertical sequence, particularly in the updip section. Parasequence bounding surfaces here are often cemented and/or intensely bioturbated and correlate downdip with a marine flooding surface. Each facies association within a parasequence has a characteristic shale distribution which facilitates correlation of internal heterogeneities on well logs. 3-D mapping of individual parasequences provides guidance for subsurface correlation at common (0.5-1.0 km) well spacings
Shales are divisible into minor flooding surfaces (feldwide Kv barriers) and several more restricted intra-parasequence types, relating to predominantly autocyclic events. Correct identification of the specific shale types in the vertical sequence uses outcrop dip-log, gamma ray and core analysis (i.e., data obtainable downhole). These results allow more accurate prediction of internal heterogeneity geometries and architecture in shoreface reservoirs and should provide data sets and rule bases for reservoir modeling and simulation.
AAPG Search and Discovery Article #91007© 1991 AAPG International Conference, London, England, September 29-October 2, 1991 (2009)