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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 reservoir analysis for a heavy oil field near Plover Lake, Saskatchewan (Figure 1), where Nexen Inc. has applied both hot and cold production methods. Oil sands of the Devonian-Missippian Bakken Formation are found in NE-SW trending shelf-sand tidal ridges that can be up to 30 m thick, 5 km wide, and 50 km long. Overlying Upper Bakken shales are preferentially preserved between sand ridges. The Bakken Formation is disconformably overlain by Lodgepole Formation carbonates (Mississippian) and/or clastics of the Lower Cretaceous Mannville Group. Since sandstones have larger S-wave velocities (and hence lower VP/VS ratios) than shales, VP/VS maps from multicomponent seismic data help to identify thickening sand layers within the target zone. This analysis of an initial 3D-3C survey is described in a recent paper by Lines et al. (2005). In the future, we plan to examine changes within the reservoir due to cold production by the use of time-lapse seismology. 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
Methodology and Preliminary Results
The
Figure 2 shows
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 The complete reservoir characterization involves going beyond analysis of logs and seismic data. An examination of core from the Plover Lake field is being completed in order to understand more completely the reservoir rock properties and the permeability barriers due to shale layers. The inhomogeneities in the reservoir can be more completely understood by examining core, such as that shown in Figure 4. By examining these core samples, we realize the possibility of permeability barriers and the need for more sophisticated reservoir models and the need for enhanced seismic resolution. Additionally, we need to understand more completely the reservoir changes by using time-lapse seismology and rock physics measurements to link time-varying seismic properties to reservoir conditions. Further experiments are being planned.
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 reservoir changes due to cold production. Such reservoir changes have been modeled numerically but require further verification through physical modeling. Due to subtle nature of production effects, it is our opinion that cold production reservoir effects could best be detected by repeated time-lapse multicomponent surveys. The differencing of time-lapse surveys should eliminate lithology effects and emphasize effects due only to cold production. For this reason, a time-lapse multicomponent survey is being proposed to answer the reservoir monitoring questions for the Plover Lake field. The time-lapse seismic results and the well information can be used to update the reservoir models.
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 characterization of a heavy-oil reservoir; The Leading Edge, 1134-1136.
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