American Oil and Gas Reporter - July 2015 - 48

SpecialReport: Horizontal Well Operations
In this case, he says, refracturing can
be used to connect more reservoir volume
to the wellbore.
The second condition for a refrac candidate is a mechanical or geological failure that is causing a loss of connectivity
between the well and the reservoir. In this
case, Abou Sayed says, refracturing can
reconnect the wellbore to the reservoir.
In both cases, he advises, existing
production needs to be protected.

tage of them by putting pressure on existing wells to restimulate rather than taking
a negative frac hit."
He says the resulting uplift can last for
a year or more. Hundreds of wells show
signs of passive refracturing in the Haynesville and now serve as an analog for refracturing uplift, he adds.
Abou-Sayed says the uplift potential
shown through passive refracturing inspired him to study wells for the potential
of active refracturing. "It is critical to analyze the potential outcome for each well,
both to identify the best candidates and to
reduce risk," he says. "If certain conditions
exist and the design is improper, the well
can be lost."
Many factors come into play in evaluating potential refracturing opportunities.
Abou-Sayed proposes a disciplined well
analysis workflow that reviews in detail the
well condition, performance and potential.
During the technical evaluation, AbouSayed advises engineers to focus on the
weakest link. Sometimes this is the mineralogy. "Clay volume can make a big difference in relative rock hardness, for ex-

Passive Refracturing

One of the interesting effects of
downspacing and drilling offset wells is
unintentionally stimulating nearby older
wells, says Abou-Sayed. Offset well impacts have been seen up to a half mile
away, he says, varying by shale play, reservoir quality, and presence of natural fractures. These impacts can both stimulate or
damage production.
Operators can improve results if they
understand the dynamics within the field
and between old and new wells, says
Abou-Sayed. "Frac hits are a fact of life
for shale plays," he remarks. "Take advanFIGURE 1

Increasing Value

Refrac Well Candidate KPIs

Increasing Value
Increasing Linear

V-Shaped

Decreasing Linear

Key Performance Indicators
➢ Cum Production: Increasing from low to high
➢ % Recovered or Remaining GIP: V-shaped factor
➢ Initial (Gas Rate * FWHP):
Increasing from low to high

48 THE AMERICAN OIL & GAS REPORTER

➢ Current (Gas Rate * FWHP):
Decreasing from low to high
➢ NRI: Increasing from low to high
➢ PV10: Decreasing from low to high

ample," he mentions.
He says in a strong rock such as the
Barnett Shale, the weakest link may be the
proppant, which may crush with enough
pressure. If the rock is soft, as it is in Haynesville, the weakest link may be rock
creep, which accounts for many conductivity issues, he says, adding that rock
creep can lead to fracture closure and loss
of conductivity.
A thorough risk assessment should be
performed. Among the many signs of trouble, Abou-Sayed says, are:
* Scaling;
* Fault proximity;
* Large doglegs;
* Weather induced casing stress;
* Corrosion;
* Carbon dioxide and hydrogen sulfide;
* Pressure on the annuli; and
* Cementing issues.
Well age is another important factor.
"There are many cases of new wells that
have been stimulated passively, but the effect is small," Abou-Sayed observes.
"Older wells get better results and also
present lower risk to existing production."
Economic Evaluation

Key performance indicators (KPIs)
can help identify better refrac candidates,
Abou-Sayed says. As shown in Figure 1,
the candidate well selection process can
be guided by KPIs such as rising cumulative production, initial productivity (IP)
and net revenue interest, and falling current rate and present value of estimated net
future revenues at an annual discount rate
of 10 percent. To these many curves,
Abou-Sayed adds the percentage of remaining recoverable hydrocarbons in
place. Together, he says, they highlight the
subset of wells with the greatest additional production potential.
These wells can be reviewed in light of
refracturing cost and an operator's overall portfolio, Abou-Sayed says. Because
they are in production, he adds that it is
critical to include delayed production in
the calculation. "The goal is to add production and reserves, without risk to existing revenue," he emphasizes.
He says more monitoring and analysis
will contribute to refrac knowledge, enabling
engineers to select better candidate wells.



American Oil and Gas Reporter - July 2015

Table of Contents for the Digital Edition of American Oil and Gas Reporter - July 2015

Contents
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American Oil and Gas Reporter - July 2015 - Contents
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