American Oil and Gas Reporter - August 2015 - 57

derstimulated wells. "In the progression
of almost any play, the completion design
evolves over time," he observes. "We
started conservatively, with wider cluster
spacings and smaller stimulation volumes.
Now, we complete wells with tighter spacing and much larger stimulation volumes."
That means, Hunter posits, that older
completions left rock unstimulated.
The nine wells Encana chose to refracture averaged 10,000-12,000 feet total
vertical depth with laterals around 4,000
feet. "At the time these were drilled, we
were drilling section-long laterals only,"
Hunter recalls.
He says the wells were in core areas
of the Haynesville and typically had
smaller hydraulic fracture jobs. "We
learned that bigger jobs led to better
results, so the smaller jobs were deemed
understimulated," he says.
"We played around with our design,
including fluid type and perforation strategy," Hunter continues. "We tried pumping into initial perforations, and also shot
(new perforations) to try to get closer to
our optimum cluster spacing."
He says the team used a decision
matrix to select the safest and best options
for diversion, and chose chemical diversion. "In the future, we may try mechanical
diversion also," Hunter allows. "It carries
higher costs and risks, but may yield
better results."
He says Encana bull-headed into open
wellbores with the intent of sealing off
the most depleted perforations. There was
some evidence of scaling and fracture closures, which Hunter says he believes were
addressed by pumping high volumes.

production profiles to rate the wells."
He says the team is collecting realtime pressure, and gas and water production rates to model performance.
Refracturing has proven a good strategy
in the Haynesville, affirms Hunter. After
initial experimentation, he says Encana
has stabilized its refracturing costs there
at about 10 percent of the cost to drill
and complete a new well. "Return on investment for our Haynesville refracs has
looked very encouraging," he announces.
To date, Hunter says refracs have been
limited to wells that are near uneconomic
production rates, which he says helps to

ensure that refracturing has the best chance
to demonstrate incremental production
and reserves. While production rates following refracturing have not reached
initial rates, he says the wells are economic,
and Encana continues to investigate diversion methods to increase pressures and
total stimulated rock volume.
"Refracturing is definitely a promising
application in almost every play because
of the continuing evolution of completion
design," Hunter concludes. "Revisiting
wells in this manner provides a very economical way to tap reserves that otherwise
would have been left behind."
❒

Monitoring Results
"The biggest prize I see is accessing
new rock, which gives us both increased
reserves and accelerated production," assesses Hunter.
He says he is actively evaluating how
well the diversion has worked, and is
eager to determine whether it is nearwellbore or far-field.
Encana does quite a bit of modeling,
Hunter mentions, so it can match a well's
actual to predicted performance. He says
this process helps verify the designation
of wells as understimulated.
"One of our biggest questions, once
we got started, was whether the refrac
would provide additional reserves or
merely accelerate production," Hunter
relates, noting that Encana wanted to do
both, and based on results thus far, has
been successful.
"We are monitoring four wells with
microseismic to give us an idea where
the frac fluid went and what was stimulated," he reports. "We also use our own
AUGUST 2015 57

American Oil and Gas Reporter - August 2015

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