Elena Morettini2, Gregor P. Eberli1, Keith.d. Rawnsley2, Wilhelm Kolkman3
(1) Comparative Sedimentology Laboratory, Miami, FL
(2) Shell International Exploration and Production, Rijswijk, Netherlands
(3) PDO, Muscat, Oman
ABSTRACT: Combining High Resolution Sequence Stratigraphy and Mechanical Stratigraphy for Improved Reservoir Characterisation, Fahud Field, Oman
In the Fahud field (Oman) the integration of hierarchies of sequence stratigraphic units and of fracture systems has proven to be crucial to explain the distribution of mechanical and flow units. The study focuses on the middle Cretaceous Natih E interval, a 170m thick carbonate sequence which exhibits heterogeneities in facies, reservoir quality and fracturing typical of the Natih reservoir as a whole.
A core based High Resolution Sequence Stratigraphic analysis has led to the subdivision of the Natih E reservoir into 4 orders of cyclicities (from 6th to 3rd order). Each cycle consists of a transgressive and regressive hemicycle with characteristic facies and rock properties. The facies and diagenesis of the higher order cycles vary according to their position within the 3rd order sequences.
Similar to the stratigraphy, an imbricated hierarchy of fractures and faults is proposed, following analysis of core, bore-hole images, seismic, tracers and production data. Some elements of the geomechanical hierarchy can be correlated to the sequence stratigraphic subdivision, expressing the relationship between fracturing and the depositional and diagenetic architecture of the strata. As an example, the increased amount of emersion horizons and dolomitisation in the regressive cycle of the 3rd order sequences correlate with more densely fractured brittle horizons, while the more homogeneous transgressive hemicycle is less prone to fracturing. The turnaround between transgressive and regressive hemicycles form boundaries between two mechanical units.
The combination of sequence and mechanical stratigraphy provides a framework for the correlation of facies and mechanical units across the field. In turn, the facies and mechanical units are related to reservoir quality and fracture distribution for consistent upscaling into large-scale reservoir models.
AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado