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3-D Seismic in the Glennpool Area, Northeastern Oklahoma*
By
Christopher L. Liner1
Search and Discovery Article # 40040 (2002)
*Adapted for online presentation from a presentation to the Tulsa Geological Society, January 8, 2002
1Department of Geosciences, University of Tulsa, Tulsa, OK ([email protected]). Acknowledgment is made to D. Kerr and M. Kelkar, DOE project managers for geology engineering, respectively, for well data, especially those from Self #82, and to Producers Oil, Opseis, and Mercury International Technology in relation to the 3-D seismic data.
In 1996 a small 3-D seismic survey was acquired on the
west edge of the Glenn Pool oil field, near Tulsa, Oklahoma, to map a producing
120-acre Ordovician Wilcox 
structure
. The goal was to establish a template for
the detection of such structures elsewhere. Among other results, the project
revealed the added value of 3-D imaging even in areas of dense well control and
the misalignment of time and depth structures.
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The objectives of the project are: · Leverage DOE project well information. · Provide an analog for Ordovician Wilcox exploration. · Get a view of the Pennsylvanian Glenn interval adjacent to Glenn Pool oil field. · Test small-scale 3-D seismic survey in Northeastern Oklahoma. There
are a total of 17 wells in Sections 19/24, N17N, R12E (Figure
1). Production was
discovered in June, 1985, in the Wilcox Sandstone (Ordovician Simpson
Group) at a Self unit #82, in Section 21, T17N, R12E, is located approximately 2miles from the area of the 3-D survey. The suite of logs includes DIL, LDL, BHC, CNL, GR, and SP.
– Sonic+Density => velocity X density = Impedance –
Sonic => velocity => time/
Using the sonic and density logs from the Self #82, an acoustic impedance log was prepared (Figure 2). The
sonic log can be ignored if the sonic values are predictable from the more
common density log. In the case of the Ordovician Wilcox Sandstone (Figure
3), the relation of sonic to density values suggests that density values
of themselves may be satisfactory. On the other hand, plots of the sonic
vs. density values for the Pennsylvanian Glenn Sandstone (Figure 4) and
for the entire stratigraphic interval (Figure 5) are such that the sonic
values cannot be ignored in calculating acoustic impedance for synthetic
seismograms. Figure 6 shows the velocity (from sonic values) in Self #82,
from 300 ft to total Features of 3-D seismic data used in this study are: – Vibroseis, with bin size of 55 x 55 ft – 141 E-W lines x 145 N-S lines – 1420 acres, 2.2 square miles – 1 sec, 2 ms – Frequency band--15-120 Hz
Based on the calculation in equation (1), the 55-ft bin size is a little too large because fault imaging is degraded and dips greater than 34o are also degraded.
Bin <Vint / (4 fmax) = 15000 / (4 X 120) = 31 ft (1)
The vertical resolution is shown by equation (2) to be 62 ft. Correspondingly, the Wilcox, with thickness of 34 ft or less, is a “thin bed.” Lateral resolution, given in equation (3), is 155 ft, or approximately 2 bins. Structural resolution is 11 ft, as derived in equation (4) and illustrated in Figure 7.
VR = Vint / (4fdom) = 15000 / (4 X 60) = 62 ft (2) LR = 2 X VR = 144 ft (~ 2 bins) (3) DZ = (VavgdT)/2 = 1000 X .002 / 2 = 11 ft (4)
Data footprint is shown by the images of the survey area in Figure 8, with outline of live traces (Figure 8A) and outline of the area with well spots (Figure 8B). Data cube is illustrated in Figure 9, with a time (or horizontal) slice and two vertical slices. The data in the study area are noisy, reflecting a rough terrain and near-surface issues, but there is good frequency. The challenge is how to improve the data. Improved quality of the data is illustrated in Figure 10, with the original time-slice map and the resulting enhanced map after smoothing, and in Figure 11, which shows a vertical profile, also with enhancement by smoothing.
With
the data described above, a well-
The following are conclusions from this 3-D study, some 1420 acres in size, of an oil-productive area, near Tulsa in northeastern Oklahoma: · Data improvement through smoothing by time slice (or FXY deconvolution). ·
Time · Postage-stamp sized 3-D seismic surveys can add detail (and detail adds value).
Liner, C.L., 1999, Elements of 3-D seismology: Tulsa, PennWell, 438 p. |
Figure
1.
Figure
2. Acoustic impedance log of Self #82.
Figure
3. Density vs. sonic values for Ordovician Wilcox Sandstone in Self #82,
showing a fair level of correlation (R2 = 0.6319).
Figure
4. Plot of density vs. sonic values for Pennsylvanian Glenn Sandstone in
Self #82 does not show a significant correlation between them.
Figure 5. Plot of density vs. sonic values for the entire stratigraphic
interval in Self #82 does not show a significant correlation between them.
Figure
6. Velocity (sonic) log of Self #82 plotted according to time, with
formation tops.
Figure
7. Structural resolution, as illustrated by minimum step down (dt), is
determined to be 11 ft, with the assumption of perfect removal of shallow
effects.
Figure
8. Map of image area of 3-D seismic survey (A). B shows well spots.
Figure
9. Components of data cube (time slice above vertical slices).
Figure
10. Time slice map--original version and enhanced version after
time-slicing smoothing.
Figure
11. Seismic profile showing improved quality by smoothing.
Figure
12. 
Figure
13. Enlargement of 
Figure
14. Ordovician Wilcox 
Figure
16. Detail well-
Figure
17. Seismic tracking, utilizing time-plot of sonic log and seismic
profile
Figure
18. Seismic tracking, illustrated by 3-D auto-tracking of events.
Figure
19. Seismic tracking, illustrated by seismic profile with tracked events
and overlay of time-plot of sonic log (left); Ordovician Wilcox amplitude
and time 
Figure
20. Time 
Figure
21. 
Figure
22. Comparison of 
Figure
23. 3-D representation of Ordovician Wilcox 