American Oil and Gas Reporter - July 2019 - 66

SpecialReport: Reservoir Characterization
phase to determine if differences in results
could be attributed to completion design
or differences in rock properties between
the two wells. The rock MSE trajectory
plots for all four Wolfcamp study wells
are shown in Figure 1. They illustrate the
differences in well paths and rock properties along each of the laterals, as represented by the different colors used to
represent rock MSE values. The same
color scale is used in all images.
The degree to which differences in
rock properties (as represented by rock
MSE) can affect the stimulation treatment
pressure responses depends on the completion design method, the average rock

MSE values within each completion stage,
and the heterogeneity of the rock MSE
values among the various perforation
clusters within each treatment stage.
Wolfcamp Wells
On Pad 1, Well A (engineered completion) and Well B (base line design)
were completed simultaneously in the
Wolfcamp with a single fracture equipment setup. The separation distance between the two wells was considered
sufficient to minimize interference between the induced fractures from the
two wells. The rock MSE and gamma
ray plots for Well A (Figure 2) show

FIGURE 2
Rock MSE and Gamma Ray Readings in Wolfcamp Well A
Wolfcamp Well A

Rock MSE

Gamma Ray (MWD)

Gamma Ray (Wireline)

Heel

Toe

FIGURE 3A
Wolfcamp Well A Stimulation Treatments ISIPs
3,500

3,000

ISIP (psi)

2,500

2,000

1,500

1,000

Heel
500

Toe
Wolfcamp Well A

66 THE AMERICAN OIL & GAS REPORTER

differences in rock properties at both
the heel and toe, with increasing variability at the approximate center of the
lateral. The images also show good
depth control, and indicate that changes
in rock MSE properties occur where
the gamma ray profiles show similar
changes (however, it should not be inferred that rock MSE values directly
correlate to gamma ray values).
Treatment pressures while completing
the Pad 1 Wolfcamp wells showed identifiable relationships between fracture
treatment pressure responses and rock
properties, as represented by the average
rock MSE values within each completion
stage. The first observation was that the
breakdown pressures recorded during
each of the stimulation treatments tended
to increase with increasing average rock
MSE values. A second observation was
that ISIPs were generally lower in treatment stages with average rock MSE
values in excess of 50,000 psi.
Figure 3A shows how the ISIPs compare with the rock MSE profile and rock
property variability in the horizontal section of Well A. The results show that
completion stage breakdown pressures
are related directly to the average rock
MSE values in each stage. The ISIPs are
mostly independent of the average rock
MSE values above and below the critical
value of 50,000 psi. The lowest ISIPs
are found in the section of the lateral
where rock MSE values are highest, increasing as rock MSE values decrease
as the completion progresses toward the
heel of the well.
Well B's rock MSE profile was computed after it had been completed with
the base line design and placed on production. The data showed a more uniform
profile throughout the entire length of
the Well B lateral as compared with
Well A. Based on the more homogeneous
nature of the rock MSE profile, it might
be expected that the breakdown pressures
and ISIPs would mirror the results in
the toe-downward heel section of the
Well A lateral, where there was greater
similarity between the rock properties
in the two wells. In fact, the opposite
was true.
More than 70 percent of the stimulation
treatments in Well A generated more net
pressure based on ISIP comparisons than
the corresponding stimulation treatment
stages in Well B. The breakdown pressures
during Well B treatments were more ran-

American Oil and Gas Reporter - July 2019

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