American Oil and Gas Reporter - December 2020 - 47

SpecialReport: Well Completion Technology
This change ties in with the preference
for regional sands and helps to reduce
fluid viscosity needs. These trends are
evident in the Williston Basin, where operators largely have replaced coarser
20/40 with 40/70 and 100-mesh as they
have switched from gels to slickwater
systems with friction reducers, and also
have replaced ceramics with northern
white sand.
Similar trends are evident in the Permian Basin and Eagle Ford, but in these
plays, operators are switching from northern white to regional sands. The Powder
River Basin is the only tight oil province
that still uses a large percentage of 20/40mesh sand and some RCS.
Fracture Conductivity
Choosing an economical proppant that
will hold up to stress, time/corrosion,
fluid and crushing, while offering the
highest possible conductivity, is difficult.
This analysis examined 1,500 proppant
field samples collected during the past
eight years from 100 operators and 75
manufacturers. It included a range of
proppant types-from sintered bauxite and
ceramics to sand and RCS-from wells in
the Williston, Powder River, D-J, Eagle
Ford and Permian.
The laboratory test database includes
145 regional brown sand samples and

685 northern white sand samples from
the D-J, Eagle Ford and Permian. Tests
were performed at 6,000 psi constant
stress to determine crush pressure, percent
crush fines, conductivity, permeability
and width. Fracture conductivity is the
product of the proppant permeability and
the closed fracture width on proppant.
Under the same test conditions, median
100-mesh and 40/70-mesh white sand
provided 1.8 times and 2.4 times more
conductivity, respectively, than regional
sand (Figure 2). Proppant mesh size is
even more important. The 20/40 white
sand had eight times the median conductivity of the 100-mesh regional sand.
But while regional sands have significantly lower conductivity values than
white sand, they also cost significantly
less. The question is whether using regional
sands hurts well performance in any way.
To help answer this question, the analysis
compiled oil production data from 1,770
white sand and 300 regional sand wells
in the Eagle Ford, and 1,050 white sand
and 350 regional sand wells in the Permian.
Production was normalized per lateral
foot (bbl/ft) over 365 and 730 days.
The results indicate that the wells
stimulated with regional sand perform
very similarly to the wells stimulated
with white sand. Considering both the
fairly large sample size and the lab test

conductivity results, one may expect a
more significant performance difference
if higher fracture conductivity significantly drives well performance. What
explains this?
Summarizing the results of the analysis
in a qualitative way, the minimum fracture
conductivity needed for the range of permeabilities encountered in unconventional
plays decreases with the tighter fracture
spacing and shorter fracture half-lengths
characteristic of high-intensity completion
designs. The traditional definition of dimensionless fracture conductivity (FcD)
assumes constant reservoir deliverability
during the early time flow period, which
is very high. Over time, as fracture interference sets in and flow begins to transition
away from linear flow, reservoir deliverability declines and the required fracture
conductivity decreases.
In other words, high-intensity horizontal
completions with today's tighter cluster
and frac spacing require much less fracture
conductivity (generally below 10 millidarcies-ft) than widely spaced clusters
or vertical well completions in unconventional reservoirs. The move to mitigate
fracture-driven well interference with
shorter and more precise frac lengths additionally reduces fracture conductivity
requirements for most unconventional
permeability scenarios.

FIGURE 2
Conductivity of Field Samples of Regional versus White Sands at Different Mesh Sizes

1400

Cond (mD-ft)

1300

20/40

Regional Sand, 40/70
Regional Sand, 100
White Sand, 20/40
White Sand, 30/50
White Sand, 40/70
White Sand, 100

1500
1400

30/50

1300

1200

1200

1100

1100

1000

1000
40/70

900
800

900
800

700

700
1.8x increase
from regional to
white (100 mesh)

600
500

2.4x increase
from regional to
white (40/70)

400

Cond (mD-ft)

1500

600
500
100
400
40/70
100

300
200

300
200

100

100
0%

5% 10% 15%

20%

25%

30%

35%

40%

45%

50%

55%

60%

65%

70%

75%

80%

85%

90%

95% 100%

% of Total Running Sum of Number of Records

DECEMBER 2020 47
American Oil and Gas Reporter - December 2020

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