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Shale gas extraction: frac water treatment

By 15 September 2016case, oil, pcf

The Client
The Client is a company which makes part of a Group based in the Eastern Europe and specialized in drilling activities and well services for the exploration/extraction industry.

The Client’s needs
Shale is a sedimentary rock that is predominantly comprised of consolidated clay-sized particles. Shale gas is produced from organic-rich shale formation, that typically function as both the reservoir and source for the natural gas (90% methane). It is an important source of natural gas in the United States, Canada, Europe, Asia, and Australia.

The gas stored in micro pores and trapped in shale at low permeability, cannot move easily without artificial fractures. To create additional permeability, the combination of sequenced hydraulic fracture treatments and horizontal well completions has been crucial in facilitating the expansion of shale gas development. Wells are drilled either vertically or horizontally and are hydraulically fractured to stimulate production of the shale gas: water is pumped at high pressure in the deep subsurface and has to be recovered and treated.

The Solution provided
The wastewater treatment plant supplied to the Client includes a clarifloculation and press-filter systems, followed by a two-steps evaporation plant. First, the wastewater passes through the clarifloculation unit where chemicals are dosed to precipitate part of the suspended solids and heavy metals, then the press-filter removes solids from the aqueous fraction.
Clarified water containing organic pollutants and highly concentrated in chlorides and sulphate is then sent to the EVALED® evaporators. The first step is made up of three EVALED® PC E8000, each one with a capacity of 8,000 lt/day of distillate and a specific energy consumption of 0.15 kW/h per liter, which recover about 70% of the inlet flow rate. The concentrate of this first evaporation phase is used to feed two EVALED® evaporators type PC R2000, each one with a capacity of 2,000 lt/day of distillate and a specific energy consumption of 0.12 kW/h per liter, employed to further reduce the waste volume of 1.5 times. The outcoming distillate is discharged on soil while the concentrate is collected and disposed by a waste contractor company.

Results & benefits
The EVALED® units PC E8000 produce a fluid concentrate containing up to 300 g/l of dissolved solids, while the R2000 units’ concentrate contains up to 450 g/l of salts.
Evaporation plant’s performance allows an excellent yield in terms of quality of the distillate and reduction of wastewater volume.
Table below show physical-chemical characteristics of frac water and distillate after evaporation.

Parameter U.M. Frac water Distillate
pH 6 -7 7 – 8
Suspended solids mg/l 2000 – 4000 < 5
TDS 105°C % 3 – 10 < 0.1
Conductivity µS/cm 40000 – 65000 50 – 200
COD mg/l 1500 – 5500 150 – 200
Chlorides mg/l 15000 – 45000 < 50
Sulphates mg/l 1000 – 6000 < 10
Oils mg/l 1000 – 2000 < 50
Calcium mg/l 200 -1800 (*) < 2

– (*) before clariflocculation
A further value added offered by EVALED® units applied to hydrofracking job is the opportunity to move the units on the base of the drilling site’s location.