Chemical Technology May 2016

The potential of water re-use in shale gas bed

fracturing in South Africa

by Carl Schonborn, Pr Eng

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.

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. Table 1: Estimated water needs for drilling and fracturing wells in some USA shale gas fields

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.

Volume of Drilling Water per well (l)

Volume of Fractur- ing Water per well (l)

Total Volumes of Water per well (l)

Shale Gas Field

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

* Drilling carried out with ‘mists’ (less water) or oil-based muds for deep horizontal well completions.

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

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Chemical Technology • May 2016