American Oil and Gas Reporter - December 2016 - 64

SpecialReport: Well Stimulation & Completion Technology
The first measurement (A) was to be
performed after the geophysical company
had deployed the receiver stations and
transmission equipment, but before mobilizing any hydraulic fracturing equipment. Without the noise clutter caused
by fracturing operations, this measurement
potentially could be compared to the
fourth measurement (D) to difference the
detectable proppant.
Measurement B was designed to occur
immediately prior to placing the detectable
proppant in the stage 16 plug-and-perf
operation and serve as the base-line response to be differenced from measurement C, which was to be performed immediately after completing stage 16. The
response of measurement B would include
any geophysical response generated by
the plug-and-perf operations on the first
15 stages, as well as ambient noise generated from fracturing.
To minimize ambient noise, all unnecessary equipment was shut down and
treating iron was disconnected during
both measurements B and C. The goal
was to ensure a similar ambient noise

environment for both measurements and
minimize noise effects on differenced
signal processing, so that changes between
the measurements would be attributable
to the detectable proppant.
Measurement D would be obtained
after the frac fleet left location to serve
as a companion to measurement A for
differencing the signal responses. Moreover, lab experiments suggested that the
electrical conductivity of the detectable
proppant would increase as stress on the
proppant increased, leading to a stronger
signal to surface.
Since the reservoir consisted of very
low-permeability rock, the design team
expected the fractures would remain open
for several days. Accordingly, measurement D was planned for a time after the
fractures had closed. In reality, however,
fracture analysis during treatment indicated
closure was occurring in less than one
hour. This, along with the fact that the
fracturing equipment would not be off
location until after the successive stimulation of three more wells on the pad, led
the team to change measurement D to

occur only 14 hours after acquiring measurement C.
Operational Results
Stage 16 was designed to utilize 410,000
pounds of 20/40-mesh proppant, with the
first 182,000 pounds consisting of uncoated
white sand and the detectable proppant accounting for the remaining 228,000 pounds.
The treatment went well, with no adverse
effects seen on the fracture fluid system.
However, the conveyor belt "sanded
off" with only about half of the detectable
proppant pumped. The decision was made
to flush the proppant to the perforations,
fix the problem, and then attempt to place
the rest of the detectable proppant. This
was accomplished with all 228,000 pounds
of detectable proppant placed. It was during this short shutdown in the middle of
the stage that pressure decline analysis
showed a much higher-than-anticipated
formation leak-off rate and indicated fracture closure would happen in hours rather
than days (shortening the time between
measurements C and D).
From an operational viewpoint, the

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American Oil and Gas Reporter - December 2016

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