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Abstract
Chapter from: SG
42: Applications of  3-D Seismic Data to Exploration and Production
Edited by:
Paul Weimer and Thomas L. David Author:
Mike Burnett
Published 1996 as
part of Studies in Geology 42
Copyright © 1996 The American Association of Petroleum
Geologists. All Rights Reserved. |
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*Editorial Note: Page numbers in this digital version
(HTML and PDF) do not correspond to those of the hardcopy.
Otherwise, the two are the same.
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CHAPTER 5
Chapter 5: 3-D
Seismic Expression of a Shallow Fluvial System in West Central TexasMike Burnett* |
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Burnett,
M., 3-D Seismic expression of a shallow fluvial system in West Central
Texas, in P. Weimer and T. L. Davis, eds., AAPG Studies in Geology No.
42 and SEG 3-D Geophysical Developments Series No. 5, AAPG/SEG, Tulsa,
p. 45-56. |
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Mississippian
Lime at approximately 5300 ft (1615 m), the Caddo Lime at 5000 ft (1525
m), the Strawn sand at 4500 ft (1372 m), and the lower Canyon-age Palo
Pinto reef at 3000 ft (915 m) (Figure 2). Two wells producing from the
Mississippian strata within 2 mi (3.2 km) have a combined cumulative production
of 650,000 BO, and the Caddo, Strawn, and Palo Pinto have added more than
5 MMBO from 20-30 more wells. The nearest shallow pay is encountered in
Gunsight sands of the Cisco series approximately
7 mi (11.2 km) to the south.
A 14-mi2 (36-km2)
3-D program was acquired in eastern Baylor County, Texas, during the fall
of 1992. This program was designed to image Canyon, Strawn, and Mississippian
objectives. These horizons have all produced oil in the area, and the 3-D
survey was designed to enhance further exploration potential in these horizons.
However, the focus of this
paper is on a Pennsylvanian (Cisco age) unit much shallower in the section,
this unit being responsible for significant production in Concho County,
at the southern end of the Eastern Shelf. The location of the 3-D survey
coincides with a Cisco fluvial system studied by Brown et al. (1990). The
3-D survey provides evidence of an additional relative lowstand in sea
level that occurred early during deposition of this unit. A well was subsequently
drilled expressly to test this newly identified unit. Excellent agreement
was found between the resulting log and the geology indicated by the 3-D
data. This survey appears to show details of a fluvial channel system including
point bars, mid-channel bars, levees, and flood deposits.
3-D SURVEY PARAMETERS
In the late summer of 1992,
a group of mineral owners and option holders agreed to a joint shoot of
8000 acres in eastern Baylor County. A program was designed for a high-resolution
survey with the parameters listed in Table 1. |
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ABSTRACT
3-D surveys have proven
to be a powerful structural risk reducer for oilmen in West Central Texas.
While the biggest structures were found using single-fold and 2-D common
depth point (CDP) shooting, the success rate for stepout Mississippian
and Canyon reefs drilled on 3-D surveys has increased substantially in
this area: 3-D surveys have gained wide acceptance by the oil community
in North and West Central Texas.
Whereas 2-D has been relatively
ineffective in stratigraphic situations, this paper will showcase a 3-D
survey which was used as a tool to pinpoint a shallow 1500-ft (460-m) meandering
channel in the upper Pennsylvanian Cisco system.
Regional studies report evidence
of a lowstand of sea-level for this formation, locally called the King,
which occurred near the end of deposition (Brown et al., 1990). The 3-D
data appear to demonstrate the presence of another relative lowstand of
sea level, which occurred early during deposition of this formation.
Significant detail can apparently
be seen in these data, including point bars, levees, and overbank deposits.
The data appear to correlate with all logs that penetrate the 3-D volume:
i.e., where a well penetrates the channel location depicted in the seismic
image, the logs show evidence of a channel.
This 3-D survey was designed
for objectives at 3000-6000 ft (425-1830 m). Because of this, the fold
at the shallow fluvial unit is quite low (three- to four-fold). Additionally,
the calculated bandwidth of the data is extremely high, in the 200 Hz and
greater range. These data were acquired with an I/O II system and deep-hole
dynamite, illustrating the increase in resolution available with modern
24-bit systems.
Because an oil show was reported
in this zone during drilling for a deeper objective, a well was drilled
to test a point bar identified in the 3-D data. Although no oil was found,
an excellent point bar was encountered, which further authenticated the
seismic survey's ability to provide stratigraphic detail about this shallow
fluvial unit. This is significant, because most of the oil remaining to
be found in this and other areas will come from stratigraphic traps. |
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