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by Carl Schonborn, Pr Eng
Shale Gas
Field
Volume of
Drilling Water
per well (l)
Volume of Fractur-
ing Water per
well (l)
Total Volumes
of Water per
well (l)
Approximate Number of
40 000 (l) road tankers
Barnett Shale
1 500 000
8 700 000
10 200 000
250
Fayetteville Shale 230 000*
11 000 000
11 230 000
280
Haynesville Shale 3 800 000
10 000 000
13 800 000
350
Marcellus Shale 300 000*
14 400 000
14 700 000
370
Table 1 presents estimated per well water needs for four
shale gas fields in the United States of America.
Froma paper, ‘Modern Shale Gas Development in the United
States for the US Department of Energy by GWPC and ALL
Consulting – Tulsa Oklahoma’ [1], there is discussion about
the ultimate location of fracturing fluids after drilling and
fracturing of a shale bed. Unrecovered fluids, if any, will be
located in the natural shale bed pores and some will occupy
the micro-pore space vacated by the gas that is produced.
Also, some of the fracturing fluids remain stranded in
* Drilling carried out with ‘mists’ (less water) or oil-based
muds for deep horizontal well completions.
6
Chemical Technology • May 2016
New water treatment technologies and new
applications of existing technologies are
being developed and used to treat shale
gas produced water. The treated water can
be reused as fracturing make-up water,
irrigation water, and in some cases even
drinking water. New approaches and more
efficient technologies are needed to make
treatment and re-use a widespread reality.
The potential of water re-use
in shale gas bed
fracturing in
South Africa
T
he drilling and hydraulic fracturing of a horizontal
shale gas well may typically require 7,5 – 15 mil-
lion litres of water [5], with about 12 million litres
being most common. The volume of water needed may
vary substantially between wells and the volume of
water needed per metre of well appears to be decreas-
ing as technologies and methods improve over time.
fractures within the reservoir rock and heal after
fracturing,
thus preventing the fluids from flowing back to the well.
There are two sources of water that emanate from the
hydraulic fracturing of shale beds. Flowback water and
Produced water.
Flowback water
is a water-based solution that flows back
to the surface during and after the completion of fracturing.
It consists of the fluid used to fracture the shale. The fluid
contains clays, chemical additives, dissolved metal ions and
total dissolved solids (TDS). Most of the flowback occurs
in the first seven to ten days while the rest can occur over
a three to four week time period. The volume of recovery
is anywhere between 20 % and 40 % of the volume that
was initially injected into the well, ie, 2,5 - 5 million litres of
water. The rest of the fluid remains absorbed in the shale
formation.
Produced water
, in contrast, is naturally occurring wa-
ter found in shale formations that flows to the surface
throughout the entire lifespan of the gas well. This water
has high levels of TDS and leaches out minerals from the
shale including barium, calcium, iron and magnesium. It
also contains dissolved hydrocarbons such as methane,
ethane and propane.
Some of these stranded fluids may flow back to the well in
very small volumes over an extended time span. By pursuing
the pollution prevention hierarchy of ‘Reduce, Re-use, and
Recycle’, statutory bodies are examining both traditional
and innovative approaches tomanaging shale gas produced
water. This water is currently managed through a variety of
mechanisms, including underground injection, treatment
and discharge, and recycling.
Table 1: Estimated water needs for drilling and fracturing wells in some USA
shale gas fields