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The AAPG/Datapages Combined Publications Database
Houston Geological Society Bulletin
Abstract
Abstract: Stratigraphic Details Illuminated Using Modern
3D Seismic Techniques in Upper Cretaceous Lenticular
Reservoirs, Optimizing EOR Production in the
Gulf Coast with CO2
Denbury Resources, Inc.
Plano, Texas
The five major Lower Tuscaloosa (Upper Cretaceous age) oil
fields of southwest Mississippi were discovered in the 1940s
and 1950s and were developed on 40-acre spacing to provide
apparently abundant well control to delineate reservoir
limits.
However, upon closer inspection, via detailed subsurface work
utilizing existing well control and available whole core data,
abrupt
reservoir
variations in these stacked fluvial and transitional
marine sand sequences became evident. A review of these
depositional processes revealed the limits of relying on
apparently high-density well control alone when implementing
an EOR (tertiary) CO2 project. Early recognition of flow units
is critical to the success of a CO2 flood. The CO2 process
is extremely sensitive to pressures and pressure variations, as
viscous fingering and gravity segregation can have an adverse
effect on flood performance. This realization drove Denbury
Resources, Inc. to formulate a proprietary 3D seismic plan in an
effort to optimize well locations by accurately defining
reservoir
limits (edges) while imaging multiple channels.
In 2001, Denbury Resources began to acquire proprietary 3D shoots for each of their five Lower Tuscaloosa CO2 tertiary floods in southwest Mississippi. The sequence of 3D shoots beginning with the Little Creek complex in 2001, and followed by Mallalieu in 2005, the McComb area in 2006, and Brookhaven and Cranfield in 2007 depict the acquisition and processing advances realized in less than a decade. Full utilization of the geological well data set combined with the latest 3D interpretation software provides a visualization method to spatially depict these complex reservoirs and the future opportunity to monitor the CO2 sweep efficiency via time-lapse 4D seismic*.
Although each of Denburys 3D surveys has resolvability issues
due to limited bandwidth and frequency content, this does not
impede the detection of channels and determining relative reservoir
thicknesses. Channel detectability is readily accomplished by
seismically picking a regional conformable stratigraphic event
below the Lower Tuscaloosa reservoirs, flattening on that picked
event, and then generating stratigraphically conformable (stratal)
slices. These
reservoir
sands tune at certain frequenceies which
correspond to a temporal thickness related to actual sand thickness
and fluid content. We have combined four seismic attributes
including up to three frequency volumes to detect these changes
in
reservoir
thickness and/or fluid content. This combined image
simultaneously displays spec decomp attributes in 3D space and
the interpreter can animate through the slices in subsampled time
increments to reveal increased stratigraphic detail.
Denbury Resources latest generation of reservoir
maps incorporate
the results of the 3D spectral decomposition interpretation and
has significantly enhanced the understanding and management
of the five Lower Tuscaloosa EOR (tertiary) CO2 floods.
*A companion two-year joint study now under way is utilizing
Denburys newest 3D control, which was shot in 2008 over a
portion of Delhi Field (Tuscaloosa and Paluxy) in northeast
Louisiana. The Reservoir
Characterization
Project Phase XIII,
via the Colorado School of Mines, includes a relevant time-lapse
multi-component 9C4D seismic
monitoring
program to better
image, depict, and manage a CO2 flood in a highly heterogeneous
series of multi-stacked lenticular bar and channel reservoirs.
C Channel Stratal Slice via Spectral Decomposition in GeoModeling