Chemical Technology May 2016

WATER TREATMENT

While a TDS of 5 000 mg/l is the minimum threshold for a water to be considered brine, the typical range is 30 000 to 100 000 mg/l. In South Africa drinking water must meet the require- ments of SANS 241 [4], which specifies, amongst other constituents, a maximum allowable value in mg/l of Nitrate, N<11, Sulphate, SO 4 <250, Fluoride, F<300, Chloride, Cl<200 and Sodium as NA of about 10. Natural formation water has been in contact with the reservoir formation for millions of years and thus contains minerals native to the reservoir rock. The salinity, TDS, and overall quality of formation water vary by geologic basin. After initial production, produced water can vary from brackish to saline to supersaturated brine (50 000 mg/l to >200 000 mg/l TDS) [5], and some shale gas operators have reported TDS values greater than 400 000 mg/l. The variation in composition changes primarily with changes in the natural formation water chemistry. TDS concentration is calculated as the sum of the con- centrations for Na + , K + , Mg 2 + , Ca 2 + , Cl-, SO 2 -, TAL, NO 3 -, F-, PO 4 3 - and NH 4 + in a sample filtered through a 0,45 µm filter [6]. See Table 2 on page 8. One factor in shale gas water use is that operators need this water when drilling and hydraulic fracturing activities are occurring, requiring that the water be procured over a relatively short period of time, and these activities will occur year-round. Operators may need to store water for later use. At some point, the water that is recovered from a gas well makes a transition from flowback water to produced water. This transition point is sometimes identified according to the rate of return measured in m 3 /day and by looking at

The costs of transporting water from the source to the well site can quickly and dramatically exceed the simple cost of obtaining the water [2]. Regulation of impacts on water quality in South Africa In South Africa the National Water Act, No 36 of 1998, states in the preamble that one of the objects is: ”Recognising that the protection of the quality of water resources is necessary to ensure sustainability of the nation’s water resources in the interests of all water users.” [3] What this means is that hydraulic shale bed fracturing becomes a water use, thus requiring a water use license. The Act should be studied to understand the ramifica- tions in more detail, in particular: • Water use • Prevention and remedying effects of pollution • Determination of quantity of water which may be allo- cated by the responsible authority • Licences for use of water found underground on property of another person • Regulations on use of water • Controlled activity • Declaration of certain activities as controlled activities • Water classification. Water can be classified by the amount of TDS (Total Dissolved Solids) per litre: Fresh water < 1 000 mg/l TDS

Brackish water 1 000 to 10 000 mg/l TDS Saline water 10 000 to 30 000 mg/l TDS Brine > 30 000 mg/l TDS

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Chemical Technology • May 2016