American Oil and Gas Reporter - August 2017 - 54

SpecialReport: Hydraulic Fracturing Technology
viscosity development can be obtained
in a variety of water types, usually with
reduced viscosity when compared with
cleaner water sources.
VFR fluids can provide higher fracture
conductivities through different mechanisms. First, since higher proppant concentrations can be transported and placed
with a viscosified fluid, VFR can achieve
higher fracture conductivities than lowviscosity slickwater. Second, higher retained fracture conductivities are observed
with VFR systems than with linear and
cross-linked gels.
For example, testing performed at an
independent third-party laboratory showed
a 96 percent regain conductivity for the
VFR at a 3.0 gpt concentration compared
with 60 percent regain for a linear guar gel
at a concentration of 30 pounds per 1,000
gallons (ppt), and only 33 percent regain
for a 15 ppt cross-linked gel. The higher
regain conductivities show that the VFR
fluid will tend to provide cleaner hydraulic
fractures and better well production.
Finally, since the VFR system is run
as a liquid additive on the fly, viscosity
changes can be made as required during
a job. On-the-fly viscosity adjustments
may be made to lower friction reducer
loading if a job is proceeding with no
problems to reduce chemical cost, to increase viscosity to facilitate placing higher
proppant concentrations or larger proppant
volumes than originally designed, or to

help mitigate the effects of "tight spots"
(areas of fracture width restrictions, in
which higher viscosity helps move proppant beyond the tight points).

Eagle Ford Case Study
To date, the PAM-based VFR system
successfully has pumped more than 15,000
total frac stages in multiple basins, including in the Eagle Ford Shale and the
Permian Basin Wolfcamp and Spraberry
plays.
The Eagle Ford is considered a "transitional" shale, with facies exhibiting
both brittle isotropic properties and ductile
anisotropic properties. In general, transitional shales respond well to hybrid-type
fracturing treatments that initially utilize
a low-viscosity fluid to promote fracture
complexity and a higher-viscosity fluid
in later stages to prop open the main
fracture wings.
The VFR fluid system was used to
complete two Earthstone Energy-operated Eagle Ford wells in the northern
liquids-rich portion of the play near
Flatonia in Fayette County, Tx. In this
area, the Eagle Ford formation is not as
thick or as thermally mature, and it has
somewhat lesser natural fracturing (the
Eagle Ford's characteristics change substantially across the southwest-to-northeast strike of the play, with pressure
gradients, total organic content and mineralogy varying significantly).

Earthstone's frac fluid selection evolved
from hybrid designs to using fully crosslinked fluids in 2014-15 to increase the
amount of proppant placed during each
stage. Although positive production results
were observed with cross-linked gels,
low oil prices mandated a need for lower-cost completions. In 2016, Earthstone
switched to a VFR system with the goals
of creating more fracture complexity
using a less-viscous fluid, placing similar
proppant volumes as hybrid and crosslinked designs, reducing completion costs,
simplifying operations, and achieving
production results comparable to or better
than previous designs.
Earthstone's general frac design strategy in the Flatonia area is to develop a
significantly complex fracture network
during the early portions of treatment,
followed by packing the fracture network
with higher concentrations of larger-sized
proppant. To accomplish this on these
two wells, a low concentration of VFR
was used for the first portion of the job,
followed by increasingly higher viscosities
of VFR fluid to transport higher proppant
concentrations and pack the fracture network during later stages.
The perforating strategy consisted of
five clusters spaced at 40 feet. A tapered
perforation design, with fewer heel-side
shots and more toe-side shots, was employed to promote higher cluster efficiency.
Table 1 shows an example pumping sched-

TABLE 1
Pumping Schedule for VFR-Based Treatments (Earthstone-Operated Eagle Ford Wells)
Stage
#
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17

Description
Load Well
15% HCL
Pad
0.25 ppg 100 Mesh
0.5 ppg 100 Mesh
0.75 ppg 100 Mesh
1.0 ppg 100 Mesh
1.25 ppg 100 Mesh
1.5 ppg 100 Mesh
1.75 ppg 100 Mesh
2.0 ppg 100 Mesh
1.5 ppg 40/70 Mesh
1.75 ppg 40/70 Mesh
2.0 ppg 40/70 Mesh
2.0 ppg 30/50 Mesh
2.5 ppg 30/50 Mesh
Flush

Fluid Type
Slik-Vis VFR
Slik-Vis VFR
Slik-Vis VFR
Slik-Vis VFR
Slik-Vis VFR
Slik-Vis VFR
Slik-Vis VFR
Slik-Vis VFR
Slik-Vis VFR
Slik-Vis VFR
Slik-Vis VFR
Slik-Vis VFR
Slik-Vis VFR
Slik-Vis VFR
Slik-Vis VFR
Slik-Vis VFR
Slik-Vis VFR

Stage Stage
FR
Liquid Liquid
Conc. Conc. Volume Volume
(PPA) (gal/M) (gal)
(bbl)
1,000
24
3,000
71
0.50
40,000
952
0.25
0.50
30,000
714
0.50
0.50
30,000
714
0.75
0.50
30,000
714
1.00
1.00
30,000
714
1.25
1.00
35,000
833
1.50
1.50
35,000
833
1.75
1.50
35,000
833
2.00
2.00
35,000
833
1.50
2.00
40,000
952
1.75
2.50
40,000
952
2.00
2.50
27,000
643
2.00
2.50
11,500
274
2.50
2.50
9,200
219
15,000
357

54 THE AMERICAN OIL & GAS REPORTER

Cum.
Cum.
Liquid Liquid
Stage
Cum.
Volume Volume
Prop.
Prop. Pump Stage
(gal)
(bbl)
Prop. Type Mass
Mass
Rate Time
1,000
24
0
0
10 2.4
4,000
95
0
0
10
7.1
44,000
1,048
0
0
72 13.2
74,000
1,762 100 Mesh
7,500
7,500
72 9.9
104,000
2,476 100 Mesh 15,000 22,500
72 9.9
134,000
3,190 100 Mesh 22,500 45,000
72 9.9
164,000
3,905 100 Mesh 30,000 75,000
72 9.9
199,000
4,738 100 Mesh 43,750 118,750
72 11.6
234,000
5,571 100 Mesh 52,500 171,250
72 11.6
269,000
6,405 100 Mesh 61,250 232,500
72 11.6
304,000
7,238 100 Mesh 70,000 302,500
72 11.6
344,000
8,190 40/70 Mesh 60,000 362,500
72 13.2
384,000
9,143 40/70 Mesh 70,000 432,500
72 13.2
411,000
9,786 40/70 Mesh 54,000 486,500
72 8.9
422,500 10,060 30/50 Mesh 23,000 509,500
72 3.8
431,700 10,279 30/50 Mesh 23,000 532,500
72 3.0
446,700 10,636
0 532,500
72 5.0



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