American Oil and Gas Reporter - August 2015 - 64

THERE ARE
A LOT OF
WAYS TO
MAKE HOLES.

www.perf.com

Customized Frac Stages Improve
Completions In The Bone Spring
By Lyle V. Lehman

HOUSTON-An evolving stimulation
and completion strategy, building off an
interconnected methodology that customizes individual frac stages to quantify
permeabilities and reservoir quality
throughout the lateral, continues to yield
new insight into the economical drainage
of the triple-bench Bone Spring formation
in New Mexico's Delaware Basin.
The methodical strategy has evolved
to overcome a number of technical impediments, with early results showing
sequential improvements in per-well recoveries. Early on, the investigation reinforced the importance of selecting a
carrier fluid based on proppant transport
requirements, as well as fracture height
and breaking ability to optimize conductivity placement.
The unique flow regime and cycling
stresses of the Bone Spring also were
found to justify using more play-compatible ceramic proppant, further illustrating the elevated understanding of the
real-world trade-offs between less expensive, but equally less beneficial, technologies and practices.
One of the key learnings arising from
the study was the quantifiable impact of
lateral setting depth, which goes hand-inhand with the fluid and proppant in optimizing a frac design. Accordingly, geomechanical data collected from offset wells
were incorporated in a predrilling workflow
model, utilizing a 3-D frac simulator to
establish the optimal target zones for both
the lateral and stimulation treatments.
Complementing the stage isolation
component of the Bone Spring "boutique"
frac design, the multifaceted analysis
found that replacing basin-standard plugand-perf completions with sliding sleeve
systems enhanced completion efficiency
nearly 100 percent. Along with selective
stage isolation, a multistage port completion was shown to enhance production
results and improve the calibration of
the reservoir quality model.

Bone Spring Geology
Generally described as a thick sequence
of interbedded sandstones, carbonates
and shale, the Bone Spring overlies the
Wolfcamp Shale, the Ellenburger group
and the Morrow at depths ranging from
6,000 to 13,000 feet (Figure 1) in Southeast
New Mexico's Delaware Basin, extending
into West Texas. Each layer of the three

benches making up the Bone Spring play
consists of equally productive sand carbonate layers, although the uppermost
zone is believed to seldom develop porosity and permeability.
Before the acceleration of hydraulically
fractured horizontal wells, the Bone Spring
source rock was largely a bypass zone
for the presumably more prospective and
deeper zones. When new-generation logs
revealed a much thicker pay zone, the
Bone Spring quickly emerged as a primary
lateral target for multistage fracs, bolstered
by the superb well control when landing
horizontal sections between mature and
deeper vertical wells.
Observed permeability from production
history matching ranges from a high of
0.25 millidarcy in the second sand to a
low of 0.0044 md in the third bench. Unlike other shale plays, the Bone Spring
reservoir pressure gradient varies from
normal to only slightly elevated at 0.443
to 0.455 psig/foot.
Because of the wide variance in permeabilities, a completion/stimulation strategy was initiated to frac each stage based
on its level of permeability. Specifically,
a customized workflow, in tandem with
a patented fracture design and analysis
software, were employed to capitalize
on readily available mud log response
data to precisely plot distinct permeabilities
(reservoir quality) across the entire lateral.
The ensuing data cleared the way for the
stage-specific frac strategy, which unlike
the typical homogenous approach of uniform lateral-wide stimulation treatments,
was engineered to match the stimulation
of each zone to its degree of permeability,
thereby optimizing coverage and ostensibly
increasing cumulative production rates.
Zonal permeability isolation served as
the springboard for the systematic study,
focusing on the second and third Bone
Spring, with the objective of resolving the
five remaining hurdles to a cost-effective
stimulation and completion strategy.

First Three Hurdles
The first hurdle to be addressed in the
evolving study involved landing the lateral
to accommodate the most efficient frac
design. The primary considerations focused on the lateral length and azimuth,
followed by determining the most effective
transport fluid (the second hurdle). The
third hurdle was selecting the proppant
type best suited for the relatively high
closure pressure gradients, ranging from
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American Oil and Gas Reporter - August 2015

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