American Oil and Gas Reporter - April 2015 - 70

SpecialReport: Refrac Facts

Technology Key To Enabling Refracs
By Jamie Phillips

HOUSTON-Unconventional oil and
gas wells typically exhibit steep decline
curves, and the only way operators have
been able to maintain or grow reserves
has been to drill and hydraulically fracture
large numbers of new wells, leading to
substantial growth in U.S. tight oil production. Of course, that growth has been
based almost entirely on horizontal wells
completed with multistage frac techniques
that produce at high initial rates but
decline rapidly.
Consider, for example, the Eagle Ford
Shale, which the U.S. Energy Information
Administration reports has the highest
average per-well productivity of any U.S.
tight oil play. While the average initial
production rate more than tripled between
2010 and 2013, the first-year decline averaged 69 percent in 2013, according to
data from Drillinginfo (Figure 1). Moreover, second-year declines have increased
significantly in the Eagle Ford, averaging
nearly 50 percent for wells drilled in
2013.
At those rates, a well that came on line
in April 2013 with an IP of 350 barrels a

day was yielding about 110 bbl/d by April
2014, and would now be making on the
order of 55 bbl/d, representing an 84
percent loss of productivity within 24
months of starting production.
With historically high oil prices and
plentiful prospects making aggressive
drilling programs feasible over the past
several years, the strong IPs of new wells
more than offset the characteristic steep
decline curve of existing wells.
The furious pace of unconventional
development has slowed with falling oil
prices. Operators are finding the time to
think about ways to improve and extend
production from wells in which they already have invested millions of dollars
apiece to drill and complete.
With hopes of adding low-cost production and reserves, while boosting estimated ultimate recovery, there is a lot
of talk about refracturing wells in unconventional plays. However, the reality
is that refracturing is still in its infancy,
and the industry has much to learn about
refrac engineering best practices and technology solutions before refrac campaigns
can be expected to add significant reserves.
The situation is not unlike the ongoing

learning curve associated with optimizing
the multistage frac techniques developed
over the past decade for horizontal shale
plays.
Unfortunately, however, some of the
completion techniques that made shale
development possible also make economic
refracs difficult to achieve in these plays.
But the future will be different as newgeneration tools are employed and operators engineer initial frac treatments with
the understanding that productive wellbore
intervals may need to be accessed at
some point to pump a refrac.
Biggest Obstacle
To date, a few operators have attempted
refracturing on a limited scale and with
mixed results, and numerous papers and
articles have been written about various
aspects of restimulation: candidate selection, optimum time to refrac, reservoir
pressures, refrac design, in situ stress reorientation, etc. However, the biggest
obstacles to successful restimulation are
finding a way to isolate sections of the
wellbore to be treated and delivering the
stimulation treatment with high enough
rates and pressures to be effective.

FIGURE 1
Eagle Ford Horizontal Well Decline Curves in First 48 Months of Production
(Including All Subplays, and Oil, Wet Gas and Dry Gas)
Color by
Year
2009
2010
2011
2012
2013
2014

400

350

Daily Production (bbl/d)

300

250

200

150

100

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
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48

0
Months Produced

Source: Drillinginfo

70 THE AMERICAN OIL & GAS REPORTER

American Oil and Gas Reporter - April 2015

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