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Reservoir
Characterization
of Plover
Lake Heavy-Oil Field*
By
Larry Lines1, Joan Embleton1, Mathew Fay1, Steve Larter1, Tony Settari1,
Bruce Palmiere2, Carl Reine2, and Douglas Schmitt3
Search and Discovery Article #40274 (2008)
Posted February 12, 2008
*Adapted from extended abstract prepared for AAPG Hedberg Conference, “Heavy Oil and Bitumen in Foreland Basins – From Processes to Products,” September 30 - October 3, 2007 – Banff, Alberta, Canada
1CHORUS, University of Calgary, Calgary, AB, Canada ( [email protected] )
2Nexen Inc., Calgary, AB, Canada
3CHORUS, University of Alberta, Edmonton, AB, Canada
Enhanced production of heavy oil from the Cretaceous sands of Eastern Alberta
and Western Saskatchewan presents many challenges – requiring a more complete
description of lithology, porosity, permeability, and changes in reservoir
fluid
composition and physical properties. Our
reservoir
projects near Plover Lake,
Saskatchewan, seek to produce
reservoir
models that are consistent with all
available data, including well logs, cores, produced fluids, and seismic data.
Thus far, we have effectively used dipole sonic data and multicomponent 3-D data
to delineate sand layers effectively. Core measurements suggest that interbedded
shale layers will impact vertical permeability and consequently oil production.
In order to map production and
reservoir
changes effectively, we propose to use
time-lapse (4-D) seismic surveys to update our
reservoir
models. These seismic
measurements are coupled to laboratory measurements of Vp/Vs from core samples
and detailed oil-column profiling of fluid properties. Experience with 4-D
seismic data at nearby Bodo field, near Provost, Alberta, has shown that seismic
monitoring
can effectively map the
reservoir
changes due to cold production.
Hence, we advocate a
reservoir
characterization
strategy that involves the use
of logs, cores, and a base 3-D seismic survey to describe geology with repeated
multicomponent 3-D surveys being used to map
reservoir
changes. Our study shows
reservoir
studies on models and real data from the Plover Lake area, along with
planned future research.
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This paper examines a combined geological and geophysical For this study, the 3D-3C seismic data was acquired by Veritas DGC using the VectorSeis® digital multicomponent recording system over a 8 square kilometer surface area. Multicomponent interpretation is made possible by a few dipole sonic logs, as well as many sonic and density logs. The estimated Vp/Vs maps in this study are largely based on traveltime methods. However, a recent paper by Dumitrescu and Lines (2006) uses AVO analysis and simultaneous inversion to provide high-resolution images of the heavy oil formations. Finally, we examine cores from this area to provide a fine scale description of rock property variations in the field.
Methodology and Preliminary Results The traveltime method for creating Vp/Vs maps from multicomponent data that is both robust and straight-forward. Flat events on vertical stacks are predominantly PP reflections, but on radial stacks are mostly due to PS conversions. Hence, interval traveltimes from a radial component stack contain information about S-wave velocities and, together with the corresponding traveltimes from the vertical component stack, provide us with the necessary information to calculate Vp/Vs, the ratio of P-wave to S-wave velocities. Figure 2 shows traveltime picks for the vertical and radial components on seismic lines in Plover Lake field. The exploration targets are sand ridges within the Bakken Formation at a depth of about 800 m. For our traveltime picking, we initially used the Sparky Coal of the Mannville Group (~780 m) as a reference horizon above the Bakken and the Torquay Formation (Devonian carbonate at ~830 m) below the Bakken. Unfortunately, the Torquay is difficult to interpret on the seismic data, and it turns out that better traveltime picks can be obtained from a slightly deeper reflection (“base event” at ~1000 ms, PP time).The process of picking traveltimes was guided by the use of dipole sonic logs. These logs allowed us to compute PP and PS synthetic seismograms to aid interpretation of the Sparky and Torquay horizons throughout the vertical and radial 3D volumes. The resulting Vp/Vs maps produced a very interesting and encouraging result for lithology discrimination. On the northern half of the map shown in Figure 3, we have marked enclosed features with dark lines to indicate an eroded Lodgepole Formation. In the same figure, we have also marked a boundary along the southeastern side of the map which defines the erosional edge of both the Bakken sand ridge and overlying Lodgepole Formation. Low Vp/Vs values in the middle of the map correspond to thicker Bakken and Lodgepole, while higher Vp/Vs on the southeastern side of the map correspond to a zone where the Bakken sand and Lodgepole Formation have both been eroded. In summary, when this Vp/Vs map is compared to previous interpretations based on well data and conventional (vertical component) data, the correlation of the map to other sources of lithology information is excellent. It should be mentioned that two other Vp/Vs maps based on different horizon picks are very similar to Figure 3 - suggesting that traveltime mapping of Vp/Vs is very robust and reliable. Another encouraging note is that this Vp/Vs map is very similar to those obtained by Dumitrescu and Lines (2006) using AVO analysis.
The complete
By examining these core samples, we
realize the possibility of permeability barriers and the need for
more sophisticated
Conclusions and Future Work
The computation of
Vp/Vs maps from a
3-D multicomponent seismic survey has been very interesting and
useful in delineating lithology changes. However, it would be
interesting also to characterize
AcknowledgementsThe authors thank the Consortium for Heavy Oil Research by University Scientists (CHORUS) for support of this project. We especially thank Nexen Inc., a CHORUS sponsor, for permission to show results from their Plover Lake data. Finally, we thank Sensor Geophysical for processing the seismic data and Hampson-Russell for the use of their PROMC software. ReferencesDumitrescu, C. and Lines, L., 2006, Vp/Vs ratio of a heavy oil field from Canada, paper submitted to the 2006 CSPG-CSEG convention.
Lines, L., Zou, Y., Zhang, A., Hall, K., Embleton,
J., Palmiere, B., Reine, C., Bessette, P., Cary, P. and Secord, D.,
2005, Vp/Vs
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