Stochastic
Modeling of the Wafra Maastrichtian Reservoir, Partitioned Neutral Zone (
Meddaugh, W. Scott1, Raymond
A. Garber1, Stewart Griest2, Dennis W. Dull1,
Rebecca Latimer3, Arturo Contreras1 (1) Chevron Energy
Technology Company, Houston, TX (2) Chevron Energy Technology Company,
The Maastrichtian reservoir is one of
five prolific oil reservoirs in the giant Wafra oil field. Maastrichtian oil
production is from subtidal dolomites that average 15% porosity and 30 md permeability though porosity values up to 40% and
permeability values over 1000 md are common. Discovered in 1959, the
Maastrichtian reservoir has produced less than 1% of its 1.5 billion barrels of
low API, high sulfur oil in large part due to reservoir heterogeneity.
The carbonates were deposited on a very
gently dipping, shallow, and restricted ramp setting that transitioned between
normal marine conditions and restricted lagoonal environments. The
Maastrichtian interval is part of the Aruma Group (Tayarat Formation) and is
divided into an upper and lower portion by the Second Maestrichtian shale. The
lower interval consists largely of peloidal mud-lean dolopackstones and minor
grainstones were deposited under humid conditions during a transgressive phase
that evolved into a high stand. The upper portion consists of dolorudstones and
dolofloatstones alternating with peloid-rich, fine-grained dolostones that
grade upward into argillaceous dolowackstones and dolopackstones deposited during
a relative high-stand under arid conditions. Ten high frequency sequences have
been correlated across the field.
A detailed geostatistical model of the
reservoir constrained by the sequence stratigraphic interpretation and
stochastic seismic inversion shows the layered and compartmentalized nature of
the reservoir and demonstrates that paleotopography had a critical influence on
depositional facies and subsequent dolomitization. Analysis of FMI and
production data enabled a fracture characterization to be incorporated in the
dynamic model of the reservoir.
AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California