American Oil and Gas Reporter - November 2018 - 44

Industry In Motion
FIGURE 2
Wolfcamp Core Interval and Hydraulic/Natural Fractures
Natural Fracture
45
0'

Producing
Horizontal
Well in UW

60'

ulation technology. Results from the
SCW, subsurface proppant distribution,
and insights from other acquired datasets
are providing the basis for the research
team to visualize and describe the physical
parameters of the subsurface hydraulic
fracturing process.
Proppant Analysis

Continuous
Core Sections

Slant Core
Well

Hydraulic Fractures

Clamshell Core
Extraction Method

Hydraulic Fractures

completion of the horizontal wells. Radioactive tracers were not detected during
core logging or in drill cuttings sampling.
Cut ends of the three-foot core sections
were photographed to document their
states prior to laboratory transport.
The SCW trajectory enabled the collection of core with varying lateral distance
from adjacent producing wells to provide
insights into both the vertical and horizontal fracture geometries. Figure 2 (upper
left) shows an example of the SCW trajectory with respect to the offset producing
horizontals. During drilling operations,
cuttings samples were collected every
five feet to obtain additional proppant
and lithology information along the path
of the cored interval. Mass spectrometry
data were analyzed with the intent of assessing reservoir compartmentalization
and hydraulic fracture identification, but
did not yield any fundamental insights.
Once coring was completed, the curve
and lateral sections of the SCW were
logged utilizing a quad-combo logging
suite, including an image log (oil-based
mud imager). The log data and additional
information collected while drilling, specifically the image log, were used to supplement the core data and aid fracture
analysis in lateral sections where core
was not obtained. After logging, the well
was cased, cemented and multiple isolated
44 THE AMERICAN OIL & GAS REPORTER

gauges were installed to monitor pressures
at select intervals within the producing
wells and target formations. These gauges,
along with additional pressure gauges
placed in producing horizontals and select
offset legacy wells, were monitored for
pressure changes during production.
CT scans before removing core from
the barrels assisted in determining core
integrity as well as the best extraction
methodology, since maintaining core in
a pristine condition was critical for physical
fracture description. Figure 2 (bottom)
shows a whole core interval after using
the "clamshell" core barrel extraction
method, with a hydraulic fracture in the
right panel. CT scans were also utilized
to differentiate in situ (natural and hydraulic) fractures from fractures created
while removing core from the barrels.
The recovered core captured hundreds
of hydraulic and natural fractures, and
in many cases, captured the interaction
of a hydraulic fracture with a natural
fracture. Comprehensive hydraulic and
natural fracture characterization was performed. Figure 2 (upper right) shows a
hydraulic fracture cutting across a natural
fracture with a slight offset. Documented
SCW hydraulic fracture frequency and
complexity is considered to greatly exceed
current industry technology with respect
to hydraulic fracture modeling and sim-

The recovered core provides a unique
opportunity to not only capture hydraulic
and natural fractures, but also to capture
material contained within the fractures.
It was anticipated that proppant would
be discovered in the collected whole core
within hydraulic fractures. Following core
extraction, sludge residue was recovered
from coring operations within the core
barrels, including drilling mud, rock cuttings, proppant and aluminum shavings
generated during cutting the barrels to
remove core. A sample was collected and
catalogued by depth interval for each
three-foot cut core section. Most of the
sludge was located on the exterior of the
core, and within the core barrel.
Determining proppant distribution
within the stimulated reservoir volume
was a primary objective, so ensuring accurate and reliable proppant detection
protocols within the SCW interval was
of paramount importance. Detailed sampling procedures of proppant and associated residues were undertaken on all fracture faces, the exterior core surface, and
within core sleeves. Samples were
processed following cleaning and preparation, and the dried, segmented and
weighed samples then were scanned using
high-resolution transparency imaging.
Imaged samples were processed using
an automated image processing workflow
to detect all identifiable particles of
interest, including proppant, natural calcite
and shale.
Lateral and vertical proppant distribution has been documented via proprietary workflows developed by the HFTS
consortia, which when incorporated with
other available data, is anticipated to improve proppant distribution modeling and
simulation technologies. To identify the
origin of hydraulic fractures and proppant
located within the SCW, more than 20

American Oil and Gas Reporter - November 2018

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