American Oil and Gas Reporter - December 2015 - 59

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SpecialReport: Well Stimulation & Completion Technology
FIGURE 5
Depth View of Microseismic Events Colored by Well
And Sized by Magnitude (All Three Laterals)

monitored, given the increasing distance
and longer offsets from the receiver array.
With identical stimulation designs,
microseismic distribution with the hydraulic fracture geometry was expected to
be relatively consistent from one stage to
the other in each lateral. However, the microcosmic data showed the stages treating
very differently. Figure 5 presents a depth
view of microseismic activity, with events
colored by well.
Treatment slurry rates were adjusted
throughout the real-time fracturing operations to limit upward microseismic height
growth observed on some of the stages.
The observed microseismic event depths
indicate that despite real-time variations
in stimulation treatment rates to control microseismic height development, the microseismic distribution did not display consistent behavior with the changes implemented. There were clear variations in
height growth in the first 12 stages of the
Neal 345H.
To investigate microseismic variations in developed fracture geometry,
geomechanical and petrophysical log
measurements from the Neal 307 offset
(located less than a half mile away) were
compared with the microseismic distribution in stages 1-12 in the Neal 345H. The
upper boundary that potentially limits
upward fracture height growth and microseismic activity appeared variable from
one segment of the lateral to the next.
Downward growth showed more consistent change, with more stages completed
and more microseismic downward growth
for the stages toward the heel.

Identifying Fracture Barriers
Without a clear understanding of the
lateral changes in rock properties at different depths, it becomes more challenging to determine variations in fracture treatment pressure responses, in addition to microseismic event distribution and source
parameter. Potential fracture barriers were
identified from Neal 307 vertical logs. The
minimum in-situ stress was propagated
across a 3-D geomechanical grid, taking
into account the stratigraphic framework
from 3-D seismic (Figure 6).
Since numerous fracture barriers could
be identified by examining the contrast
from low- to high-stress regions, the mi-

croseismic height growth distribution remained inconclusive. The zone-wise consistent, laterally interpolated stress profile
appeared to match microseismic height
only on a few stages, and failed to capture
the lateral facies variability influencing microseismic fracture response.
Figure 7A shows treatment results
from the fifth stage of the Neal 345H. The
image at top left shows microseismic
events in map view colored by time and
sized by magnitudes. Microseismic events
in depth view against a zoned stress profile are shown at top right. The bottom
graph shows the treatment plot with surface pressure (red), treatment slurry rate
(blue), proppant concentration (green), microseismic event rate (bars), microseismic
event count (purple), and microseismic cumulative moment (black curve).
The data indicate the majority of microseismic activity in stage 5 developed
with upward height growth, where most
of the event density was located within the
lower-stress zones of the Wolfcamp B
(above the wellbore). A few events propagated shallower into the Wolfcamp A,
where the 346H lateral is located, and more
dispersed events were scattered within
deeper portions of the Wolfcamp B in both
lower- and higher-stress zones. It is clear
that this stage had relatively decent height
confinement compared with the microseismic distribution on the other stages of the
345H lateral.
On the other hand, the stage 10 stimulation saw the majority of microseismic
height growth (Figure 7B) occur down-

FIGURE 6
Neal 345H Microseismic Events by Stage
Displayed Against a Zoned Stress Profile
Very few events surpassing potential frac barriers.
Possibly dry events as they appear to be strictly
disconnected from the main event clouds nearer
to the wellbore.

Potential frac barriers limiting upward growth.

Neal 345H
landed in
Wolfcamp B.

Potential frac barriers limiting downward growth.

Color
Stage

Very few events surpassing potential frac barriers.
Possibly dry events as they appear to be strictly
disconnected from the main event clouds nearer
to the wellbore.

All stage events are sized by the magnitudes.
Events are colored by stage.

DECEMBER 2015 59

American Oil and Gas Reporter - December 2015

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