American Oil and Gas Reporter - July 2018 - 70

SpecialReport: New Tech & Geosciences
Seismic monitoring has the potential to play a critical role in
managing unconventional reservoir development and improving
the economic return on investment. Integrating 4-D multicomponent seismic, vertical seismic profiling and microseismic
surveys provides a unique opportunity to monitor permeability
and stress field conditions over time as wells are drilled,
completed and produced.
By characterizing the reservoir under dynamic instead of
static conditions, the permeability field created by hydraulic
fracturing can be monitored over time. Natural fractures, faults
and stress states profoundly influence the permeability field
created by hydraulic fracturing. The permeability field is a continuum, and it constantly changes as a reservoir is developed.
Monitoring changes in the permeability field can reveal the
region where permeability is enhanced because of stimulation
and how it changes in time, while enabling a better understanding
of the effectiveness of hydraulic fracturing in accessing the hydrocarbons present in the low-permeability rock matrix.
Anadarko Petroleum Corp. and the Colorado School of
Mines Reservoir Characterization Project teamed to conduct an
integrated dynamic reservoir characterization study of a portion
of the Wattenberg Field. Time-lapse multicomponent data were
acquired during the hydraulic fracture stimulation of 11 horizontal
wells as part of a well spacing test within a one square-mile
section called "Wishbone," as shown in Figure 1A (the dark
lines are faults at the top of the Niobrara).
The integrated study sought to determine which parts of the
reservoir were being accessed by hydraulic fracturing operations
and which parts of the permeability continuum were being
FIGURE 1A
Seven Niobrara and Four Codell Horizontal Wells in
Wishbone Section (Dark Lines are Faults)
N

monitored by the various seismic methods. The integration of
seismic and engineering technologies helps optimize well
spacing and other parameters, including completion type and
number of stages (Figure 1B). It is worth noting that the cost of
conducting seismic monitoring operations on the one squaremile Wishbone site is less than half the cost of drilling and
completing a single well in the section.
4-D Multicomponent Monitoring
Seven of the 11 Wishbone horizontals were landed in the
Niobrara and four were landed in the Codell. The base line
multicomponent seismic survey was acquired prior to drilling.
During hydraulic fracturing, a surface microseismic survey was
acquired. A monitor multicomponent survey then was acquired
after the wells were stimulated, but before they were flowed
back. The well trajectories were designed to facilitate hydraulic
fracturing more than maintaining contact with the primary zone
of interest. Most wells were drilled toe-up to facilitate gravity
drainage. Formation image logs show open natural fractures as
well as a considerable number of fractures with calcite fill.
Overpressures in the Niobrara/Codell interval extend several
hundred feet above the reservoir into the basal part of the Pierre
Shale, causing stress relief in the overburden, which is a critical
factor in making the Niobrara a world-class reservoir. Evidence
of pressure compartmentalization occurs in the reservoir set up
by faulting associated with wrench fault tectonics.
Paragon Geophysical Services acquired both the postdrilling/pre-completion base line and the post-fracturing/preflowback monitor surveys. The first survey was conducted
during relatively dry conditions in early summer, but there was
considerable noise present related to operational efforts going
on in the field at that time. The second survey was completed a
couple months later, shortly before storm clouds darkened the
skies as a prelude to a "100-year flood." Paragon Geophysical
used INOVA Geophysical's wireless Hawk™ system to acquire
FIGURE 1B
Location of the Wishbone Horizontal Wells
N

Nio B Chalk

11N

Nio B Marl
N
600'

600'

900'

Nio C Chalk

Zippe

Nio C Marl
Nio D
Fort Hays

CD
10C

CD
800'

CD
950'

FMI

70 THE AMERICAN OIL & GAS REPORTER

900'

Radioactive Tracer

1,200'

r Frac

600'

Codell

Carlile FM

Multiple CFT

American Oil and Gas Reporter - July 2018

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