American Oil and Gas Reporter - August 2015 - 62

SpecialReport: Hydraulic Fracturing Technology
FIGURE 2
Mill-Out Times in Eagle Ford Well
30

Mill-Out Time (min)

A
Pl vg
ug .s
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

Composite Plug Number

ture setting. Adding these pins did not adversely affect the performance of the plug or the slip.
Three weeks later, 52 plugs were run on a two-well pad operation in the Permian Basin. While each plug incorporated the
design changes to fix issues encountered in the previous field runs,
one plug still became stuck during deployment. Examining the
plug showed that the lower slip had broken, and one slip segment
was missing. A full analysis of the plug dimensions suggested
the standoff from the minimum outside diameter of the plug and
maximum outside diameter of the slip buttons was too small. The
slips were redesigned to increase this clearance while at the same
time reinforcing them for additional strength.
A final field trial in the Permian Basin used 23 plugs in one
well. While the plugs were deployed down hole without getting
hung up, two of the plugs were initially pumped past their desired setting depth. When the operator attempted to pull the plugs
up to location with wireline, they would not move. This led the
design team to believe that the upper slip was breaking during
run in, which would not be an issue until the plug was pulled up
hole.
The slip was subsequently reinforced to increase the break force
on the upper slip, and the problem has not been observed since.
After this final revision, the composite plug technology has performed with extremely high reliability in more than 19,000 runs
in all U.S. basins.
Functionality And Efficiency

The field trials helped prove the plug's functionality and efficiency in a variety of well architectures, while allowing design
problems to be identified quickly and addressed. The culmination of the design, laboratory qualification and field trial work
was a more compact and lighter plug with a smoother outside diameter body and minimal metal content to provide the necessary
sealing strength while circumventing many of the deployment and
milling challenges common to legacy plugs.
For example, the high-integrity seal provided by a largely composite-based plug allows each plug to be 21⁄2 to 9 inches shorter
than other composite frac plugs. In a multistage completion with
62 THE AMERICAN OIL & GAS REPORTER

35 plugs, using a shorter composite plug can significantly reduce
the amount of material to mill through, on the order of 18 feet
in some cases. Reduced milling footage, of course, translates directly to rig time savings.
The composite material also allows for rapid drill-out using
conventional drilling equipment, including coiled tubing drilling
motors. The plug's average mill-out time of 10.5 minutes per plug
represents a 50 percent reduction in the milling times typical of
traditional plugs.
Figure 2 shows mill-out times in an Eagle Ford well. Each plug
was milled much faster than the average mill-out time for plugs
used in previous wells (far left), with many plugs milling out in
half the time. In addition, the composite material consistently mills
into small, lightweight cuttings to minimize the risk of plugging
surface equipment.
Further refinements include adding an optional pump-down
ring on the mule shoe. This ring has a slightly larger outside diameter than the plug, which creates a larger overall outside diameter for the plug assembly to capture the full hydraulic energy of the fluids conveying the plug down hole. A pump-down
ring can pump the plug into position more quickly and with less
water.
This was demonstrated in a field trial in which two plugs were
run into a well. One plug was equipped with a pump-down ring
and the other was pumped without a ring. For the plug run without the pump-down ring, 300 barrels of fluid were required to get
the plug to the setting depth 10,873 feet in the well and with a
maximum line speed of 219 feet/minute.
The plug with the pump-down ring installed was deployed with
a maximum line speed of 380 feet/minute and required only 147
barrels of fluid to get the plug to a target depth of 10,596 feet.
Extrapolating these results to a well with 30 frac stages, the reduced fluid requirement would result in a 50 percent reduction
in the amount of water required to pump a plug to its location.
Since the field trials and subsequent design changes, the new
composite frac plug has set successfully and held pressure more
than 99.9 percent of the time in thousands of well runs. The technology is suitable for a wide range of applications-including vertical, deviated, horizontal and multilateral wellbores-and also enables underbalanced drill-out of multiple plugs to protect sensitive formations.
Ultimately, composite plug technology's deployment flexibility, reliable sealing during stimulation, and easy mill-out combine
to make it an economically attractive and efficient component of
the lower-cost completion in any oil price environment.
❒

MATTHEW CRUMP is composites product line manager at Weatherford. He joined the company in 2011, and
previously served as product line manager of open-hole
packers and as product line champion for completions. Before joining Weatherford, Crump served in business development and project management roles at Baker Hughes,
and as a project manager at Redding Linden Burr Consulting Engineers. He holds a B.S. in mechanical engineering
from Texas A&M University and an M.B.A. in finance from
the University of Houston.

American Oil and Gas Reporter - August 2015

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