American Oil and Gas Reporter - December 2020 - 44

SpecialReport: Well Completion Technology
As the shale revolution has pushed
into lower-quality reservoirs, lateral
lengths, stage counts, and proppant volumes have increased along with costs
and pressures related to lower commodity
prices. The concept of dimensionless conductivity has led the industry to use
cheaper and lower-quality proppant materials for high-intensity completion designs, first moving away from ceramics
and resin-coated sands (RCS) in favor of
northern white sand, and more recently
displacing northern white with regional
sands mined in West and South Texas.
To understand how different proppant
types and mesh sizes have performed in
unconventional plays, data from the Williston, Permian, Eagle Ford, Powder River
and Denver-Julesburg basins was evaluated
using a combination of techniques, including multivariate statistics, lab conductivity testing, detailed fracture and
reservoir modeling, and direct well group
comparisons. Using a variety of data
sources, analysis techniques and economic
criteria provides a more holistic approach
to proppant selection.
Then, the results were combined with
economic analyses to provide a perspective
on proppant selection criteria. The comparisons were anchored to permeability
estimates from production history matching and diagnostic fracture injection tests
and thousands of well site proppant con-

ductivity tests to determine dimensionless
conductivity estimates that best approach
what is obtained in the field.

ever-denser frac fairways by:
· Drilling longer laterals to access
more rock at a lower incremental cost
with a reduced environmental footprint;
· Increasing stage counts and stage
intensity/reducing spacing;
· Increasing proppant mass and fluid
volume;
· Using lower-quality proppants;
· Using slickwater with high-viscosity
friction reducers (fewer and smaller volumes of chemical additives to place a
pound of sand in the formation); and
· Increasing pump rates.
As the industry has ramped proppant
mass to 2,000 pounds per lateral foot or
higher in many plays, it has shifted toward
lower-cost regional sands to achieve justgood-enough economics, marginalizing
the use of higher-quality RCS and ceramics
in the process. Studies have shown that
larger proppant mass more than makes
up for poorer proppant quality in the production response of horizontal shale wells.
A typical horizontal well has hundreds
of fracs contributing to wellbore flow,
which means that each frac carries only
a small proportion of the total hydrocarbon
flow. This dramatically lowers the need
for fracture conductivity.
Moreover, the industry is demonstrating
a growing preference for smaller proppants, first shifting from 20/40- to 40/70mesh, and more recently, to 100+ mesh.

Just-Good-Enough Economics
Typically, proppant selection is based
on crush resistance to stress loading,
fracture conductivity under various flow
conditions, and of course, cost. However,
dimensionless fracture conductivity is
the main driver of well performance as
it relates to proppant selection, since it
includes the relationship of fracture conductivity provided by the proppant relative
to the rock's actual flow capacity (the
product of permeability and effective
fracture length).
The analysis indicates how much fracture conductivity is adequate for a given
effective fracture length and reservoir
permeability and in shale formations. It
also examines the economics of achieving
" just-good-enough " target conductivity-
either through less proppant mass with
higher-cost proppants, or more proppant
mass with lower-cost proppants-as well
as mesh size considerations.
Figure 1 is a compilation of public
data from several sources for liquid-rich
shale basins. It illustrates trends in stage
count, proppant and fluid volumes, and
injection rate normalized for lateral length
during the past decade. The technology
has focused on creating ever-larger and

FIGURE 1

Max Pump Rate/
Stage Length
(bpm/ft)

Stage Spacing
(ft/stage)

Completion Parameters Normalized by Lateral Length for Five Liquids-Rich Basins

400
200

Average

0
0.6
0.4
0.2

Proppant Mass/Lat
Length (lbs/ft)

Total Clean Volume/
Lat Length (bbl/ft)

0.0
40
20
0
2K

1K

Basin
WILLISTON
POWDER RIVER
D-J
EAGLE FORD
PERMIAN

0K
2010

2011

2012

2013

2014

2015

Year of Production Start Date

44 THE AMERICAN OIL & GAS REPORTER

2016

2017

2018

2019
American Oil and Gas Reporter - December 2020

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