American Oil and Gas Reporter - PBIOS 2014 Official Program Guide - 180

profile along the wellbore with each treatment.
DTS data are acquired by emitting a
laser light pulse at the surface from a DTS
interrogator. The light pulse travels at a relatively known speed with a known wavelength, and is returned to the same DTS
interrogator. The fiber optic cable imparts
a backscatter effect to the traveling light

as it moves down the well. The backscatter signal contains anti-Stokes and Stokes
Raman components. The amplitude difference between the two Raman components
at a certain point provides the capability
to acquire temperature information. To be
effective, the amplitude difference must be
calibrated at a known temperature point.
Once calibration is complete, the DTS ca-

FIGURE 2
Post-Fracture Model and DTS Results for Four-Interval Treatment

Target perforation
intervals

FIGURE 3
Thermal Recovery for Four-Interval Treatment
50
10,400
10,450
10,500

Temperature (F)
110
130

Expected vertical
coverage based
on thermal
recovery results

170

6:31:17 a.m.
During injection
10-min recovery
30-min recovery

10,550
Measured Depth (ft)

150

60-min recovery
10,600

6-hr recovery
12-hr recovery

10,650

24-hr recovery
48-hr recovery

10,700
10,750

10,800

10,850

Perforation intervals
10,900

180 THE AMERICAN OIL & GAS REPORTER

ble provides accurate temperatures along
the fiber optic cable's entire length.
Because the fiber optic cable was deployed permanently behind casing in a vertically oriented wellbore, it was assumed
that distributed temperature results would
relate directly to the hydraulic vertical fracture height near the wellbore. Thermal recovery was assessed after each stimulation
treatment to monitor the temperature profile before the near-wellbore area was restored to geothermal temperature. If no injected completion fluid was immediately
behind the wellbore, the thermal recovery
toward geothermal was expected to be very
rapid.
Figure 1 highlights the temperature profile plot using all the DTS data acquired
during all 11 stages. It shows that DTS data
were collected continuously throughout the
entire duration of the project. The initial
temperature profile is in blue and the final temperature profile is in orange. The
y axis for all plots represents the measured
depth of the wellbore at the same scale.
The color map ranges in temperatures
from 85 to 155 degrees Fahrenheit, with
the blue hues representing cooler temperatures and the red to black hues representing warmer temperatures. The horizontal
white lines indicate the measured depth of
perforations. The history plot displays the
treatment parameters for each stage over
the same time span as the color map.
For fracture modeling, a well log was
broken down, selecting data 150 feet
above and below the perforation interval
from the open-hole results. Fluid loss estimates were made based on the treatment
fluid. A pressure match was performed using the final instantaneous shut-in pressure
(ISIP), and pressure fall-off was monitored
after each stage. The open-hole logging
data were acquired, processed and reviewed before beginning completion operations. Proprietary log analysis algorithms were used that output several
processed log results and illustrated critical attributes of the formations.
Four-Perforation Cluster Stage
Figure 2 shows DTS data acquired
while fracturing a stage with four five-foot
perforated intervals. For this stage, the average flow rate was 88 barrels a minute,
and surface treating pressure averaged
5,900 psi. The total proppant placed was
stopped prematurely because of higherthan-expected treating pressures.
The blue curve in the temperature
profile plot is the preinjection curve for this
stage, establishing a base line for understanding thermal response after injection. The orange curve is a point in time
midway through the stimulation, and the
pink curve is a trace approximately 10

American Oil and Gas Reporter - PBIOS 2014 Official Program Guide

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