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Applying accommodation versus sediment supply ratio concepts
to stratigraphic analysis and zonation of a fluvial reservoir
ALLARD W. MARTINIUS , CARSTEN ELFENBEIN * and KEVIN J. KEOGH †‡
Statoil Research Centre, Rotvoll, 7005 Trondheim, Norway (E-mail: awma@statoil.com)
* Present address: Det Norske Oljeselskap ASA, Nedre Bakklandet 58c, 7014 Trondheim, Norway
Present address: Statoil ASA, 4035 Stavanger, Norway
ABSTRACT
The use of sequence stratigraphic principles as a correlation tool within fluvial deposi-
tional systems has been a topic of debate for a long time. Changes in facies stacking
patterns caused by allocyclic events are often masked or completely overprinted by auto-
cyclic events and therefore the recognition of correlative time-significant markers can be
difficult. These problems are more difficult to solve when trying to apply sequence
stratigraphic principles to subsurface well datasets. A method is presented here based on
the concepts of accommodation versus sediment supply interactions (A/S) and their
variations at a hierarchy of temporal scales. These changes lead to the development of a
pattern of overall increasing or decreasing A/S values reflected in the sedimentary
record. The key addition to existing ideas about continental fluvial sequence stratigra-
phy is the notion that the rate of fluvial aggradation through time, as controlled by the
accommodation versus sediment supply rate, is dynamic and not static. The use of the
concepts of A/S interactions allows for the fluvial stratigraphic system to be analysed not
only (or solely) in terms of regional to local base level changes that affect accommodation
but as an integrated parameter with regional to local sediment supply changes. A practi-
cal definition of base level (or stratigraphic reference level) in fluvial systems is outlined
and formulated as the lower boundary of real-time accommodation or upper boundary
of net accommodation (lower limit to erosion). In areas not directly affected by laterally
migrating fluvial channels or channel belts, the upper boundary of net accommodation
at a specific time scale can in some cases be genetically coupled to the most mature pal-
aeosols. In other cases, the upper boundary of net accommodation may be picked at a
laterally extensive caliche layer formed at a depth relatively unaffected by short-term
erosion and deposition. The method presented here is not meant as a substitute for
previous stratigraphic methods or models for fluvial systems but as an alternative to be
used as seen appropriate given the type and amount of data available. The application
and limitations of this method are highlighted in a case study from the Statfjord Group,
Statfjord Field, in the Norwegian North Sea.
Keywords: Fluvial stratigraphy, A/S hierarchy, reservoir zonation, Statfjord Group,
base level.
INTRODUCTION
three-dimensional architecture. Temporal and
spatial variations in multiple interdependent
controlling factors such as sediment supply,
hydraulic characteristics and autogenic responses
of the depositional system (Puigdefàbregas, 1993;
Hovius, 1998; Leeder et al ., 1998; Ethridge et al .,
1998; Muto & Steel, 2002, 2004; Yoshida et  al .,
2007; Muto et al ., 2007) are now also considered
One of the most important recent advances
in  sequence stratigraphy is the increased aware-
ness of the influence of temporal and spatial
variations in primary sedimentary processes and
geomorphological variability on the stratigraphic
development of depositional systems and resulting
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