American Oil and Gas Reporter - PBIOS 2014 Official Program Guide - 183

Permian Basin Reports
Upstream

Downstream

FIGURE 4
DTS and Logging Data for Four-Interval Treatment
Clear change in pressure,
brittleness, and rock properties
50
10,400

Temperature (F)
110
130

150

10,450

10,500

10,550

Measured Depth (ft)

hours after completing injection. The four
intervals are identified by the white horizontal bands. The orange curve observed
during injection showed cooling near all
four perforated intervals, indicating each
interval received fluid during treatment.
The post-stimulation temperature (pink)
did not have a consistent thermal recovery
after injection.
The areas with faster thermal recovery
represent areas where very little fluid
volume was placed by the fracture, while
areas with higher fluid volume have a slower return to preinjection temperature. It was
assumed that no fluid cross-flow occurred
after injection. There was clear separation
between the prestimulation and post-stimulation temperatures. This variance was
used to estimate hydraulic fracture height.
Figure 3 shows thermal recovery data
for this stage, with the well's measured
depth plotted on the y axis and temperature on the x axis. Each of the four perforated intervals is highlighted by the fivefoot segment to the left of the expected vertical coverage. The warmest blue trace is
the preinjection trace. The traces highlighting thermal recovery in time help establish
estimates for hydraulic fracture height at
each perforation interval. Each of the
four color bands across the traces represents the associated hydraulic fracture
height near the wellbore for each interval.
A total of 48 hours of thermal recovery data are displayed in Figure 3 to obtain the most representative output for fracture height. The orange six-hour recovery
trace has a very similar shape to the 48hour trace, but longer thermal recovery data
are always best when trying to quantify hydraulic fluid placement.
To determine upper and lower fracture
height bounds, the thermal departure from
cooler to warmer temperatures relative to
measured depth must be monitored closely. Typically, this clear change in slope
identifies the upper and lower bounds. As
defined by the expected vertical coverage
of each fractured perforation interval, the
upper and lower bounds of the hydraulic
coverage are indicated at the depths where
the thermal signature begins to break to the
slope of the blue preinjection curve.
As mapped by the DTS results, hydraulic fracture height was estimated to be
70 feet for the first perforated interval, 65
feet for the second, 55 feet for the third,

Midstream

10,600

10,650

10,700

10,750

10,800

10,850

10,900

and 60 feet for the fourth interval. That
compared with 72, 60, 53 and 60 feet, respectively, from the post-job fracture
model results. In this stage, there was clear
agreement between both hydraulic fracture
height diagnostic approaches (variances of
3, 8, 4 and 0 percent, respectively).
The next step in the analysis was comparing the mapped DTS results with
processed open-hole logging data. Because
the post-job fracture model was generated using the same open-hole logging
data, and there was clear fracture height
agreement between the two diagnostic approaches, some correlation was expected.
Figure 4 shows DTS thermal recovery results (left) and open-hole logging data
(right). The same estimated hydraulic
fracture height color bands are present
across both images to assist in defining relationships between height growth and logging results.
The areas of focus were at the upper
and lower bounds of fracture height to
identify variability in the logging results.
As indicated in the three right-hand
columns, there was a clear change in
brittleness ("x width"), formation pressure
and rock properties at each of the bound-

ary interfaces of hydraulic fracture height.
It is very possible that downward growth
from the deepest perforation was impacted by the previous fracture stage, since that
stage's fracture height had reached a
measured depth of 10,850 feet just a few
hours before.
The most significant change in the logging results at these depths was a clear decrease in formation brittleness as calculated by dipole sonic data (the wider the red
area under the x width column in Figure
4, the higher the relative brittleness). The
areas with the highest vertical Young's
modulus and lowest vertical Poisson's ratio were defined as brittle. For these four
intervals, the logging data indicated the areas with lower relative brittleness did not
fracture.
Two-Perforation Cluster Stage
Another stage included two 10-foot perforated intervals with 110 feet of separation stimulated at an average flow rate of
85 bbl/min and average surface treating
pressure of 5,300 psi. Figure 5 shows the
DTS data acquired at different points
during stimulation, with blue again denoting the preinjection curve, orange repreOCTOBER PBIOS 2014 183

American Oil and Gas Reporter - PBIOS 2014 Official Program Guide

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