American Oil and Gas Reporter - February 2018 - 65

SpecialReport: Advancing Shale Science

Approach Identiļ¬es Refrac Candidates
By Ahmed Alzahabi,
Mohamed Y. Soliman
and Marshall Watson
MIDLAND-Even as the industry
ramps new well drilling and fracturing
activity in shale plays, operators continue
to look at the potential for refracturing
existing horizontal wells. Consequently,
as they plan their initial completion designs, more operators are considering the
possibility that wells may need to be reentered at some future date to recomplete
sections of the lateral.
While refracturing technology is obviously focused on unconventional reservoirs today, refracs long have been a
viable option in conventional formations
for extending the life of producing
wells. In fact, the first targeted refrac
campaign was conducted on 71 Clinton
wells in Ohio in the early 1970s, resulting in a reported average production
increase of 4,000 barrels a well. The
possibilities to increase production and
reserves recovery are exponentially
higher in low-permeability shale reservoirs, in which only 20-30 percent of
the fracture stages may be effective-
leaving 70-80 percent contributing little
or no production.
The effectiveness of each stage in a
multistage horizontal tight oil or shale
gas well largely is dictated by the ability
to create hydraulic fractures to connect
the wellbore to natural fracture "swarms"
in the rock matrix. Given the extremely
low-permeability matrix, natural fracturing
is critical to productivity, giving hydrocarbons conduits to flow to the borehole.
However, natural fractures that contribute significantly to production early
in the life of a well can start to close
quickly, as can the propped induced hydraulic fractures connected to the natural
fractures. Refracturing can reactivate natural fractures, and perhaps more importantly, stimulate virgin portions of the
reservoir not in communication with
initial frac treatments to restore production
and flatten the steep decline curves typical
of shale plays.
While the science of refracturing shale
reservoirs is in its infancy, the early results
are promising. For instance, field studies
of successful refrac projects in the Eagle
Ford and Bakken shales show that restimulation increased reserves by 53 and

69 percent, respectively, on average. Another study of 200 Barnett Shale refracs
showed that most of the wells yielded
two-four times their initial production
rates after treatment.
There are numerous reasons for why
refracturing potentially can improve production and recovery rates in shale wells,
but there are likely many cases where
the initial fracturing job designs were
simply not effective, or where significant
volumes of rock were left untreated or
understimulated. In addition, both natural
and hydraulically induced fractures tend
to rapidly lose conductivity over time as
the in site stress field changes with depletion and proppant is flowed back
during production.
One of the most basic factors in refracturing success is selecting appropriate
candidate wells to ensure economic performance. A Texas Tech University research project evaluated 149 refrac treatments in both vertical and horizontal
wells, and culminated in the development
of a new fuzzy logic-based tool to guide
the refrac candidate selection process and
assist in planning initial completions and
refrac treatments in unconventional reser-

voirs. It uses genetic algorithms and fuzzy
logic techniques to identify candidates
based on three categories of input data:
* General information about each
well, including location coordinates, depth
indications, and the date wells started
production;
* Reservoir quality information, including net pay, porosity, saturation, permeability and pressure; and
* Stimulation information, including
the types and volumes of proppants and
fracturing fluids, perforation density and
number of zones.

HOUSTON-Rosehill Resources Inc.
has completed its acquisition of 1,940
net acres, certain mineral and royalty interests and two producing wells in the
Southern Delaware Basin in Pecos County,
Tx., for $39 million. The purchase increases the company's total net acreage
to 11,150 net acres, with more than 400
gross Wolfcamp A, Wolfcamp B and
Bone Spring locations.
The Pecos County transaction follows
Rosehill's $78 million acquisition of 4,565
net acres and producing oil and gas properties in the Delaware Basin in mid-December. The company says that transaction
nearly doubles its total net acreage, to
9,200 net acres, with the potential for additional acreage acquisitions through
March 8 under terms of the agreement.
The earlier acquisition increases the
company's horizontal drilling potential by
more than 160 gross locations, with opportunities in multiple Wolfcamp A, Wolfcamp
B and Bone Spring horizons. Rosehill adds
additional upside potential comes from
deeper Wolfcamp and Woodford horizons

as well as from shallower Avalon horizons.
Rosehill says the first purchase establishes a second core operating area in
northwestern Pecos County, and provides
enhanced size and scale for operational
efficiencies. The company adds the continuous acreage position enables 7,00010,000 foot laterals.
According to the company, its 2018
guidance assumes it will use a two-rig
drilling program for the first three quarters
of the year, with a third rig to be added in
the fourth quarter, as well as a dedicated
fracture crew for the full year. Rosehill
says it expects to drill between 50 and 54
wells in 2018, completing as many as 46.
"We believe there is tremendous upside
in our Delaware Basin assets, and we remain focused on delivering value-added
growth by executing on our plan," says
J.A. "Alan" Townsend, Rosehill's president
and chief executive officer. "Our operational plan for 2018 and preliminary forecast for 2019 is fully funded within
existing liquidity and anticipated growth
in our borrowing base."
r

Candidate Selection
The million-dollar question is why
refracs seem to work very well in some
shale reservoirs but not so well in others.
Shale is very heterogeneous, as evidenced
by very different production statistics
from wells within the same localized
play areas. Mineralogy and physics control the nature of shale heterogeneity,
but shale compositions tend to be highly
complex with random distributions of
total organic carbon and other key mineralogical, geomechanical and petrophysical parameters. The details of the

Rosehill Resources Buys Delaware Basin Acreage

FEBRUARY 2018 65



American Oil and Gas Reporter - February 2018

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