American Oil and Gas Reporter - December 2015 - 52

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SpecialReport: Well Stimulation & Completion Technology
The three laterals were stimulated in a
simultaneous zipper frac sequence with
geometric stage placement. Real-time
microseismic monitoring was used to observe the treatments and the resulting
heights and lateral extent of the hydraulic
fractures. Although identical pumping
schedules were intended initially for all
three laterals, it became apparent during
the treatments that microseismic height
growth varied significantly across the
laterals within individual stages.
Linear regression analyses showed
strong correlations between seismic Pwave impedance versus microseismic
data and fracture pressure responses,
shale mineralogy compositions, and geomechanical properties calculated from
core-supported petrophysical data. Mineralogical and geomechanical shale properties were measured directly from 3-D
surface seismic data lengthwise along
lateral trajectories at individual frac stages.
The results indicate that microseismic
fracture height variability in the three wells
was influenced most by changes in shale
stratigraphy and mineralogy composition, without a definitive relationship
with treatment injection rates. Optimal
fracture heights were observed in landing
areas with significant volumes of calcite
(Vcal), characteristic of high Young's
modulus and closure stress (variables estimated from 3-D seismic).

For validation, the production histories
of the three laterals and numerous other
wells in the field confirm a strong correlation between inverted seismic P-wave
impedance and initial 120-day cumulative
oil in landing zones with high Vcal (brittleness) and correspondingly low clay.

Wolfcamp Geology
Callon Petroleum is focused on onshore
unconventional oil and natural gas reserves, with its asset base concentrated in
the Midland Basin. Its operations are focused on horizontal drilling in several
prospective intervals, including multiple
levels of the Wolfcamp and Spraberry formations. The company operates two horizontal drilling rigs focused on five
prospective development zones.
Wolfcamp laterals are typically 5,00010,000 feet long. The lower costs associated with drilling stacked horizontals in a
chevron pattern from pads (Figure 1) improves economics, while simultaneously
completing multiple wells in a zipper sequence increases stimulation efficiency
and achieves higher initial production
rates. Obviously, increased production is
particularly critical during periods of low
crude oil prices.
The Wolfcamp formation has four independent landing zones in the Upton
County, Tx., area of the Southern Midland
Basin: the A, B, C and D (or Cline). Each

FIGURE 1
Stacked Laterals in Chevron Pattern (A)
And Wolfcamp A and B Well Spacing (B)

zone is well within the oil window, and
contains varying volumes of mineral
compositions, including quartz, limestone, clay and kerogen. In this three-well
project, microseismic data were acquired
for the Wolfcamp A and B zones only.
The Wolfcamp B generally has relatively higher initial production rates and
greater estimated ultimate recoveries than
the other zones, given its ideal mineralogy for enhanced brittleness and greater oil
saturations. The Wolfcamp A typically
contains massive carbonate detrital deposits toward its base that can act as fracture barriers. The C and D zones are deeper in the section and have higher fracture
gradients. They are increasingly influenced
by deeper-seated structures that potentially can induce geosteering challenges.
For all four zones, mineralogy compositions define the mechanical layers that
are most prone to fracturing, which is a
function of changes in lateral and vertical
depositional (mineralogical) facies. Wolfcamp mineralogy varies considerably
across the Midland Basin, as demonstrated by petrophysical logs acquired in
vertical wellbores.
Geologically, Wolfcamp rocks in the
central and southern parts of the basin are
characteristic of kerogen-rich dark shales
and interbedded detrital carbonates, muds,
sands and silts that were deposited predominately by debris/gravity flows and turbidity currents downslope from the Central Basin Platform (CBP), likely in a proximal basin plain environment. Shelf-ward
toward the CBP, carbonate deposition increases to a point where large detached
blocks of dolostone are common proximal
to the platform margin.
Consequently, the abundance and distribution of carbonate-rich detrital flows
can be used as a proxy in determining relative distance from the CBP margin,
which in turn, defines carbonate fairways prone to fracture stimulation for increased production when high grading
acreage for development.

Two Distinct Units
Each Wolfcamp zone can be subdivided into two units: a high clay volume
(Vclay) ductile "flooding surface" interval, which saw minimal carbonate shedding, and a more brittle calcite-rich carbonate "bench" interval. Operators typically land laterals below the flooding
surface and within the more brittle carbonate bench to optimally initiate wide hydraulic fracture networks near the well52 THE AMERICAN OIL & GAS REPORTER

American Oil and Gas Reporter - December 2015

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