Rock Physics
Modeling and Seismic Attributes of Carbonate Rocks in the Nesson Anticline, North Dakota
Bandyopadhyay, Kaushik1, Tapan
Mukerji1, Gary Mavko1, Charlie West2 (1)
Stanford University, Stanford, CA (2) Hess Corporation, Houston, TX
Carbonates usually show high spatial
variability of rock properties. Careful modeling that integrates large scale
structural and stratigraphic features with pore scale rock properties is
important in delineating the reservoir zones in such formations. In this paper we
present rock physics based analysis of seismic properties in a dolomite
formation in North Dakota. The reservoir rock is
highly heterogeneous. The variability in the rock properties are mostly
controlled by structural setting, stratigraphy and diagenesis. Two different
pore types, vugy porosity and micro-porosity are present in the studied region.
Vugs are open in the reservoir zones and filled with salt in the non-reservoir
rocks. Acoustic properties of different pore types are studied at well log and
seismic scale. Differential effective medium model is employed to model the
effective seismic properties. Pore space stiffness is used as an additional
parameter to explain the large variability in seismic velocities at a
particular porosity. The structural setting and proximity to major faults are
found to be important factors affecting the reservoir quality. Many of the
non-reservoir rocks showing salt-plugged porosity are in close proximity to the
large scale faults. It is hypothesized that vertical fractures associated with
the major faults controlled fluid movement and resultant deposition of salts in
the pore space. Incorporation of these fractures of scales larger than sonic
log but smaller than seismic scale into the rock physics models turns out to be
crucial in calibrating well data to the seismic. Finally we present post stack
and inverted seismic attributes to differentiate the salt-plugged zones from
good reservoirs.