American Oil and Gas Reporter - August 2015 - 114

SpecialReport: Rockies Activity Profile
FIGURE 4
Niobrara Reflection Quality before (Left)
And after (Right) Adjusting Sweep Effort
6 Sweeps/VP
8 Seconds

9 Sweeps/VP
12 Seconds

600

700

800

900

1,000
1,100
1,200
1,300
1,400
1,500
1,600
1,700
1,800
1,900
2,000
2,100
2,200
2,300
2,400

costly seismic hardware damage.
Much effort during the planning phase
also focused on accurate design testing
of the vibroseis sweep frequencies to
help avoid impacting any nearby structures.
The decision to use a wireless system
proved correct, but it posed challenges
during the acquisition stage because of
an inability to monitor field data quality
in real time. To overcome this, field data
collection was monitored daily so that
the sweep effort was maximized while
the total acquisition time stayed within
the contract requirements.
The location of underground utilities
was surveyed carefully and avoided to
help prevent damage resulting from the
weight of the vibrators. Accurate positioning of the seismic receivers was
recorded for data quality control and
public safety. In addition, traffic control
during operational hours was implemented
to help avoid congestion or accidents.
Police escorts were provided for the safety
of residents.
Figure 3A shows traffic control while
vibrator trucks work on a Greeley street.
Figure 3B shows a wireless receiver
station positioned near an intersection.
Particle-wave ground motion recorders
at every vibration point monitored the
effect of the vibrator sweeps on nearby
buildings and surface structures. The
hours of operation were restricted to 7:00
a.m. to 7:00 p.m. to help reduce any
impact on residents. Throughout approximately 30 days of data acquisition, no
major damage was recorded.
Flyers and educational material were
sent to every resident within the survey

900

1,000
1,100
1,200
1,300
1,400
1,500
1,600
1,700
1,800
1,900
2,000
2,100
2,200
2,300

10,900 ft/sec

2,400

area in advance of data acquisition, and
an open house was held for more than a
week for residents with questions regarding
the survey. Geokinetics, the seismic acquisition contractor, also set up a vibrator
truck to demonstrate the seismic operation.
Public sensitivity and total transparency
were key to the successful and smooth
operations during the survey.
Acquisition And Processing
The layout of source and receiver lines
across the 23 square-mile survey area
was highly irregular because of limitations

posed by city streets and easement geometry. Receiver lines were laid in an eastwest direction and source lines in a northsouth direction. Nominal spacing was
660 feet for receiver lines and 825 feet
for source lines. Source and receiver
spacing within the lines was 165 feet, resulting in a processing bin size of 82.5 x
82.5 feet. The nominal fold of the final
bin grid was 80.
There were 5,217 receiver points and
3,885 source points during the survey.
Sweep frequencies were nonlinear, ranging
from 8 to 96 hertz to help avoid damaging
ground roll at the lower end. Receiver
groups (six phones per group) were
planted in the ground wherever possible.
When not possible, the receiver groups
were planted in a sandbag with another
sandbag on top to help minimize noise.
Each wireless receiver group had an associated battery pack and data collection
box. Every few days, data from the collection boxes were collected and uploaded.
The most difficult challenge during
any urban survey-and the Greeley 3-D
survey was not an exception-is maintaining a sufficiently high signal-to-noise
(S/N) ratio with the presence of rigorous
engineering limitations dictated by the
proximity of vibrator trucks to residential
and commercial buildings. Sometimes,
only one vibrator out of a group of four
was used on a vibration point, with only
20 percent of force allowed.

FIGURE 5

114 THE AMERICAN OIL & GAS REPORTER

Greeley 3-D Survey Interpretation Montage
North Wattenberg Field Well Map

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*
*
*
*
*

Horizontal Niobrara Well Stats

Niobrara Vertical Type Log

Drilled in Highly Structured Area
Thick "B" and "C" Chalk Pay
Drilled Oblique to Minimum Stress
Transverse and Longitudinal Fracs
Wells Drilled Updip and Toe Up
Steered to Plan

Production Decline Curves
20,000
Target Zones
15,000

Cross-Line Section

Enhanced Well No. 1
Enhanced Well No. 2

10,000

Series 1
Series 2

500

Series 3

Wattenberg Field

Niobrara Time Horizon

1 3 5 7 9 11 13 151719 21 23

3-D Structural Framework Model
from Seismic and Well Interpretation

American Oil and Gas Reporter - August 2015

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