American Oil and Gas Reporter - August 2015 - 54

SpecialReport: Horizontal Well Operations

Pioneers See Success In Shale Refracs
By Kari Johnson
Special Correspondent

As refracturing proves itself as an effective means for increasing production
and reserves from older wells, companies
across North America are evaluating and
selecting horizontal wells that have the
possibility of improved performance following additional stimulation.
For many early candidates, these pioneering companies report, the quickest
qualification for refracturing is wide cluster
spacing. They note that early completion
designs left significant swaths of rock
unstimulated. The improved production
rates and reserves resulting from greatly
reduced fracture spacing have led them
to apply this newer design to older wells.
Others suggest restimulation may also
assist wells that have experienced damage
as a result of scaling, excessive salting,
fracture collapse, and other mechanisms.
In all cases, the goals are to accelerate
production and increase reserves without
negatively affecting the well's own current
production as well as production from

other wells in the area.
Refracturing is not without risk however, and companies report they actively
test the process and have developed detailed selection criteria and completion
designs to mitigate that risk. Over the
past few years, individual experience has
combined into a body of helpful lessons
for operators hoping to revitalize wells.
The Marcellus Shale is one region
where a key reason for revisiting wells is
that early horizontal completions had
large cluster spacings, ranging from 300
to 500 feet, observes Andrea Passman,
vice president of Pennsylvania operations
for CONSOL Energy, who notes the
company now typically spaces frac stages
150-300 feet apart.
"We can increase estimated ultimate
recoveries in some wells simply by adding
new perforations and fractures," she says.
So far, Passman reports, CONSOL
Energy has completed seven refracs of
this nature. "These were all wells in
which we felt we did not stimulate as
much rock as we could have," she says.
Down the road, Passman says, CON-

SOL also expects to revisit existing fractures to improve connectivity and conductivity.
All seven of the refractured wells were
completed originally using "plug and
perf," three to five year ago, Passman
says. For the first refrac, she says CONSOL tried mechanical diversion using
liners, but without success. For the remaining wells, it used a chemical diverting
agent to protect existing perforations and
enable new ones. "By changing the pH,
we could wash out (the well) and reopen
existing perfs," Passman explains, adding
the process worked so well that CONSOL
now sometimes uses it in initial completions as well.
"We saw initial production greater
than original IPs in some wells, and all
of them were more than 80 percent of
initial production," enthuses Passman.
In addition, she reports refractured
wells' decline curves indicate greater
EURs. "Some of the recompletions were
performed more than two years ago, so
we are pretty confident in those curves,"
she attests.

Production Data for CONSOL Marellus Recompleted Wells
6,000

30,000

5,000

25,000

4,000

20,000
Case 1-6 Recompletion
05/2014-06/2014

3,000

15,000

2,000

10,000

1,000

5,000

0
Aug-13

Jan-14
Case 7

Case 3

Jun-14
Case 6

Case 4

CONSOL Energy reports 30-month estimated ultimate recoveries
for the seven Marcellus Shale wells it has refractured increased
between 65 and 123 percent. The company says initial production

54 THE AMERICAN OIL & GAS REPORTER

0
Apr-15

Nov-14
Case 5

Case 1

Total Production Rate (Mcf/d)

Production Rate (Mcf/d)

Case 7 Recompletion
11/2013

Case 2

Grand Total

rates in some of the wells were greater than original IPs, and all
were more than 80 percent of original completion IPs.
American Oil and Gas Reporter - August 2015

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