American Oil and Gas Reporter - December 2016 - 60

SpecialReport: Well Stimulation & Completion Technology

Method Detects Proppant in Far Field
By Matt Czapski,
Keith Lynch,
Terry Palisch,
Wadhah Al-Tailji,
Lewis Bartel
and Chad Cannan
HOUSTON-Maximizing production
and hydrocarbon recovery in horizontal
resource plays requires understanding
which portions of the reservoir are adequately stimulated and contributing production, and which portions are not. The
starting point for making these evaluations
is accurately detecting the location of
the proppant pumped during hydraulic
fracturing treatments in both the nearand far-field areas of the reservoir.
In addition to traditional fracture mapping technologies, knowledge of near- and
far-field proppant distribution is necessary
to overcome single-digit ultimate recovery
factors in low-permeability, unconventional
plays. While near-wellbore detection can
determine whether all perforation clusters
received proppant and can assess the impact
of proppant overflush, proppant detection
depends on the depth of investigation of
the logging tools. In most cases, that limits
the radius of investigation to 18-24 inches
from the wellbore.
Although far-field proppant detection
techniques largely have been absent in
the industry's toolbox, the powerful insights that would come from understanding
the propped fracture network profile outside the immediate borehole radius have
led many to consider far-field proppant

detection to be the elusive Holy Grail of
fracture diagnostics. Accurately determining far-field proppant placement would
impact everything from well and stage
spacing to stage design and refracturing
candidate selection, and would allow significant optimization of diversion techniques.
To enable these benefits, a novel farfield proppant detection technique has
been developed that utilizes electromagnetic (EM) differencing and a specialty
detectable proppant. The first field test
was conducted in a horizontal Bone Spring
well in the Permian Basin, and the preliminary results show the system successfully visualized proppant distribution
in the far-field fracture network.
Energized Wellbore
The technology "electrically energizes"
the wellbore prior to and after fracturing,
using a specialty proppant that possesses
EM characteristics sufficiently different
from the subsurface medium surrounding
it. During the energizing operation, EM
responses are recorded by receivers located
on the surface or in offset wells in a time
(frequency-dependent) series of data collections. Electric current is carried to an
energizing point in the wellbore by an
insulated cable that contacts the well casing, allowing the casing to become a current line source producing subsurface
EM fields (a grounding point on the
surface completes a positive-to-negative
electric circuit).
The EM fields interact with the fracture

FIGURE 1
Candidate Well Profile with Perforation Interval
And Current Source Injection Point

True Vertical Depth (ft)

6,000

6,500

Current source
injection point

7,000

7,500
Stage 16 proposed
perforation interval
8,000
0

500

1,000

1,500

2,000
2,500
3,000
Lateral Distance (ft)

60 THE AMERICAN OIL & GAS REPORTER

3,500

4,000

4,500

5,000

containing the specialty proppant to produce secondary electric (e) and magnetic
(b) fields, which then are measured to
characterize proppant-filled fractures.
The EM proppant imaging technique is
best described as a stepwise methodology
that encompasses acquiring EM data before hydraulic fracturing, treating the
well using EM-conductive proppant, processing the recorded data, and then constructing highly-resolved 3-D images of
the "differenced" pre- and post-treatment
EM wave field propagation/diffusion results using a finite-difference numerical
algorithm.
The detection, location and characterization of the conducting proppant depends on several factors, including the
net conductivity of the fracture (proppant),
fracture volume, fracture height and
length, and the conductivity of the surrounding earth. Conventional sand, resincoated sand and ceramic proppants typically exhibit very poor EM properties,
so an integral part of developing the farfield detection technique was designing
a cost-effective proppant with high-EM
contrast properties that could provide adequate fracture flow conductivity.
After significant material research, a
ceramic proppant was developed that
features an electrically conductive coating. This approach ensured both adequate
flow conductivity and proppant strength,
while avoiding the need to develop a
completely new substrate. The primary
research work centered on coating material selection and the optimal process
for coating the ceramic proppant grains.
In addition to being electrically conductive, the coating had to be durable
and maintain its adhesion to proppant
grains throughout the fracturing process.
The coating consists of a proprietary
initial coating that promotes adhesion
of the outer conductive layer to the lowdensity ceramic substrate.
The specialty proppant possesses current conductivity, electric permittivity,
and magnetic permeability characteristics
that can be enhanced in any combination
to distinguish proppant from the surrounding geologic formation. The
stronger the EM material property contrast between the proppant and subsurface
medium, the stronger the scattered EM
wavefield recorded in post-fracturing
data acquisition.
American Oil and Gas Reporter - December 2016

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