American Oil and Gas Reporter - August 2016 - 66

SpecialReport: Hydraulic Fracturing Technology
FIGURE 4
Sample Treatment Pressure/Flow Profiles after Introducing Rate
Fluctuations for Well 6H Stages 9 (Left) and 17 (Right)

8,985

6,983.125

85

5,983.125

80

20.5

21.0

21.5

22.0

22.5 23.0 23.5 24.0
Treatment Time (minutes)

24.5

25.0

Pressure (psi)

90

7,985

90

6,985

85

25.5

19.0

19.5

20.0
20.5
21.0
Treatment Time (minutes)

21.5

Flow Rate (bpm)

7,983.125

Flow Rate (bpm)

Pressure (psi)

8,983.125

22.0

FIGURE 5
Stage-Wise Decay Rate Distributions for Wells 6H (Top) and 8H (Bottom)
300
250
Decay Rate

200
150
100
50
0
1

2

3

4

5

6

7

8

9

10 11 12 13

14 15 16

17 18

19 20 21

22 23 24 25

26

17 18

19 20 21

22 23 24 25

26

Stage #

600

Decay Rate

500
400
300
200
100
0
1

2

3

4

5

6

7

8

9

10 11 12 13

14 15 16

Stage #

FIGURE 6

Flow Rate (Mcf/d)

Flow Rate (Mcf/d)

Production Profiles for Wells 6H (Left) and 8H (Right)

0

100
200
Time (days)

300

66 THE AMERICAN OIL & GAS REPORTER

0

100
200
Time (days)

300

total frictional head loss as the pressure
pulse travels up and down the conduit, it
is intuitive to expect the decay in energy
to be higher for a longer conduit.
In the same vein, the decay also should
be higher if an extensive large-aperture
fracture network is associated with the
stage, which will consequently absorb
more energy as the pressure pulse moves
through the network. Moreover, complex
natural fracture network swarms, coupled
with hydraulic fractures, should lead to a
shorter oscillating pressure response with
a higher decay rate as a result of higher
frictional losses compared with long
planar fracture wings.
Unlike Well 6H, all of the stages in
Well 8H were completed using the traditional design with no rate fluctuations. If
variable-rate pumping opens additional
perforations and creates greater fracture
propagation/growth, one would expect
stages completed with variable-rate pumping to exhibit stronger decay in signal
strength with time than stages completed
at constant pump rates.
The study used a simple decay rate
modeling approach with an exponential
decline model to compute the decay rates
in energy observed at pump shutdown
for each of the completed stages for the
two wells. Pump shutdown procedures
for long-lateral multistage completions
can be quite random and result in highly
skewed pressure transients, which do not
allow for easy decay rate computations.
In order to resolve this issue in the study,
a simple detrending operation was carried
out using a polynomial fitting approach.
The analysis was conducted for the
first 26 of the 27 stages in Well 6H and
for the first 26 of the 28 stages in 8H.
Figure 5 highlights the modeled decay
rate for all stages analyzed. There is a
clear and discernable trend of higher
decay rates for the odd stages compared
with corresponding even stages, except
for stages 10-14 in Well 6H. The pressure
response observed for stages 10-13 follow
the skewed behavior observed in stage 9
in Figure 4. This indicates that the observed
discrepancy could be a result of a modeling
failure and not an actual indicator of
decay in pressure response (stage 26 was
the only other stage where this behavior
was observed).
The average decay rates for Well 6H
were 143 for odd stages and 95 for even
stages, while Well 8H's decay rates averaged 307 and 334, respectively. On a
percentage basis, the odd stages for Well
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