Identifying the recycling and 

treatment criteria that must be met to 

avoid scaling and enable successful 

re-use 

Timothy Cheung 

Production Chemist 

Shell Canada Limited 

October 29, 2012 

1 
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Overview 

The water cycle 

What to analyze and analysis methods: 

— Bacteria 

— Scale 

Water compatibility

Treatment required: 

— For recycling 

— For disposal

Chemical management – impact on friction reduction 

Summary
The water cycle 

Typical flowback during a well’s life: 

New Well

Water >3 m3/hr Completions 

Equipment

Temporary Pad 

Separators

Directly to Plant as 

3-phase flow

3 m3/hr < Water >2 m3/d

Water < 2 m3/d

Increasing ion 

and TDS content
The water cycle 

Source water and frac with it 

Early flowback: relatively low salinity (close to the 

water that has been used for the frac) = easy to 

recycle

Later flowback (produced water): higher salinity = 

more difficult to recycle

Recycling/Reuse: need method to recycle most of 

the water but recycling water chemistry varies 

Disposal: water is injected 
The water cycle – flowback vs. produced water 

Water (bbl/day)

Injected frac water profile

Flowback

Produced water 

Time (Days to weeks) 

Distinction between flowback and 

produced water is operationally, not 

technically defined 

Flowback = lots of frac water 

Produced water = some frac water 
The water cycle – flowback vs. produced water 

Conclusion: the two streams must be assessed differently 

Water type Flowback water Produced water 

Flow rate High Low 

Duration Days to weeks Well life 

TDS conc. Frac water TDS then 

increases 

High, determined by 

formation 

Organic polymer conc. High with return of frac

chemicals Some 

Surfactant conc. Higher conc. depending 

on frac chemical makeup 

Consistent if foamer is 

added 

Condensate conc. Some Consistent depending on 

condensate production 

Sand conc. Extremely high Low 

Other solids conc. High Depending on corrosion 
Overview 

The water cycle 

What to analyze and analysis methods: 

— Bacteria 

— Scale 

Water compatibility

Treatment required: 

— For recycling 

— For disposal

Chemical management – impact on friction reduction 

Summary
What to analyze and analysis methods – bacteria 

Bacteria control: risk of souring and/or corrosion

Analysis methods: 

BART (Bacterial Activity Reaction Test) 

Serial dilution 

TMEC (Total Microbial Equivalent Content) 

Molecular biology methods (DNA analysis) 

Field method results confirmed by molecular biology 

methods  may be different elsewhere
What to analyze and analysis methods – bacteria 

Tested fresh water and flowback/produced water 

mixtures at different points in time 

Results: 

Limited bacterial activity for SRB (Sulphate 

Reducing Bacteria) – only found some in pigging 

sample 

Low level bacterial activity identified for APB (Acid 

Producing Bacteria) 
What to analyze and analysis methods – bacteria 

Conclusions from bacteria analysis: 

Factors that make bacteria growth more difficult: 

high TDS in produced water, no guar gum (use 

polyacrylamide instead) 

Factors that make bacteria growth more easy: pH, 

TDS in fresh(er) water, temperature, sulfate level 

Biocide and dosage of biocide 

Long-term monitoring required 
What to analyze and analysis methods – scale 

Why care about ions? (solubility of some salts at 25 

deg C in water): 

Salt mg/L Comment 

NaCl (halite) 356 000 Lots of scale, evaporation 

CaSO4 (gypsum) 2 080 

SrSO4 (celestine) 129 Often with BaSO4 

CaCO3 (calcite) 53 Acid soluble, Δp issue 

BaSO4 (barite) 2.3 Difficult to remove 

Solubility generally decreases if organic solvents are present
What to analyze and analysis methods – scale 

Possible scale indicators:

Samples in recovered equipment 

Deposits at chokes or in facilities 

Tubing restriction 

Rapid loss of PI (with changes in water cut or 

analysis) 

Test problems with SSSV 

Water analysis: ion loss/modeling predicts scale 

Stimulation response 

ESEM/EDX  filter scale from produced fluids 
What to analyze and analysis methods – scale 

To avoid scale  need knowledge about ions in the 

water to judge risk level: 

Fresh water 

Flowback water 

Produced water 

Risk of iron scales, calcite, and barite 

Need the full and correct analytical techniques (lab 

analyses to include solid precipitates and anything 

unusual) 

Perform QC checks (e.g. ion balance)
What to analyze and analysis methods – scale 

Analyte Typical method 

Metals (minimum: K, Na, Mg, Ca, 

Fe, Ba, Sr, Mn) ICP, AAS 

Anions (minimum: Cl, SO4) ion chromatography 

Sulphide iodometric titration 

Density/Specific gravity hydrometer 

Conductivity/Resistivity automated conductimeter

Salinity calculated from measured chloride 

and water density 

pH at site using chemical electrode 

Alkalinity PC titrator 
Overview 

The water cycle 

What to analyze and analysis methods: 

— Bacteria 

— Scale 

Water compatibility

Treatment required: 

— For recycling 

— For disposal

Chemical management – impact on friction reduction 

Summary
Water compatibility

Analysis (mg/L) A prod. A fresh B prod. B fresh C prod. C fresh 

SO4 <1 100 - 400 80 360 <1 20 

Ba 2 200 <1 1 <1 15 000 <1 

Fe 70 <1 55 2 175 <1 

Ca 11 000 80 3 300 33 24 000 22 

HCO3 70 300 240 310 40 290 

pH 6 7.5 - 8 

TDS 270 000 1 400 50 000 1 300 230 000 400 
Water compatibility

Analysis (mg/L) A prod. A fresh B prod. B fresh C prod. C fresh 

SO4 <1 100 - 400 80 360 <1 20 

Ba 2 200 <1 1 <1 15 000 <1 

Fe 70 <1 55 2 175 <1 

Ca 11 000 80 3 300 33 24 000 22 

HCO3 70 300 240 310 40 290 

pH 6 7.5 - 8 

TDS 270 000 1 400 50 000 1 300 230 000 400 

High barium 

High sulphate 

High salinity 

High calcium 

High iron 
Water compatibility

ScaleChem modelling (thermodynamic): scaling 

potential and severity at reservoir and surface 

Several experiments undertaken to understand the 

kinetics 

Scale precipitates fast when unmitigated  onset in 

minutes, significant amounts in hours 

2 min – 60 min – 23 hr – 3 wks 
Water compatibility

Scale has been observed downhole and at surface

Inlet compressor valve – halite 

Surface tank scale/

sludge 
Water compatibility

Threats due to scale: 

Plugging/skin/production performance 

Accumulation in surface facilities, pipelines, 

completions equipment, well bores, and formation 

Under-deposit corrosion 

NORM
Water compatibility

NORM = Naturally Occurring Radioactive Material 

Main NORM source: barite  radium co-precipitation 

Mainly alpha & beta radiation (less penetrating than 

gamma rays) 

Gamma radiation can be used for screening; can be 

detected without opening equipment 
Water compatibility

Routes of exposure: 

Ingestion 

Dust inhalation  prevent material dryout

Needs special disposal (salt caverns), landfill not 

appropriate or legal 

Typical flight at 30 000 ft: 2.8 – 4.1 μSv/hr 

0.30 mSv/yr of exposure = NORM management plan 
Overview 

The water cycle 

What to analyze and analysis methods: 

— Bacteria 

— Scale 

Water compatibility

Treatment required: 

— For recycling 

— For disposal

Chemical management – impact on friction reduction 

Summary
Treatment required – recycling 

Why recycle: 

Protecting and managing water are important 

issues for both Shell and the community 

To reduce the amount of water we use and to 

minimize impacts for our activities 

So far: 

Built a water storage and recycling facility 

Building pipeline system to distribute water 

throughout the field (minimizes traffic, noise, and 

dust) 

Qualified city waste water as frac water source 
Treatment required – recycling 

Big question remaining: how can we recycle almost all 

water (including high-TDS water)? 
Treatment required – recycling 

Recycling options: 

Keep fresh and produced water separate (avoid 

incompatibilities)  operationally difficult 

Forced precipitation/secondary treatment (e.g. mix 

upstream and force scale to form)  disposal of 

NORM containing sludge difficult and expensive 

Use scale inhibitor to protect water mixtures 

Hybrid between “keep waters separate” and “use 

scale inhibitor” – inhibit the transition zone (i.e. 

where the incompatible waters mix) 
Treatment required – recycling 

Scale inhibitor requirements: 

Protect against high scaling tendencies 

Iron tolerant (iron impacts the effectiveness of 

many scale inhibitors) 

Chemical compatibility with equipment (liners, 

pipes, etc.) and frac fluids 

Chemical compatibility with production chemicals 

(corrosion inhibitor, foamer, etc.)  no plant upsets 

Favorable economics (MIC – minimum inhibitor 

concentration, cost per liter, acceptable HSE 

properties, etc.) 
Treatment required – recycling 

Iron content requires additional attention: 

Iron scales form when iron oxidizes in air 

Amount can be reduced in surface pond 

(precipitation) 

Produced water more suitable for scale inhibition 

and mixing with fresh water after precipitation 

NORMs not an issue when only iron scales form 
Treatment required – recycling 

Use of scale inhibitor, water-piping, and waterseparation strategies can: 

Enable the recycling of almost all water 

Avoid scale formation in pipelines and surface 

equipments 

Avoid NORM sludge issues 

Still allow for simple operations 
 - 

 10,000 

 20,000 

 30,000 

 40,000 

 50,000 

 60,000 

 70,000 

 80,000 

 90,000 

 100,000 

2005 2010 2015 2020 2025 2030 2035 2040 2045 2050 2055 

bbl/day 

Years 

Total Source Water, BBL/Day

Total Water for Recycle or Disposal, BBL/

Day

Treatment required – disposal 

Disposal – everyone will have a disposal stream at 

one point (based on drilling schedule): 

After drilling stops, recycling 

can’t take care of the PW; 

must dispose or discharge 

Drilling schedule interruption also 

produces imbalances 
Treatment required – disposal 

Surface discharge not an option (TDS removal leads 

to NORM-containing solids) 

Deep well discharge has challenges: 

TSS, polymer, and condensate content – requires 

treatment 

Ability of area to take large volumes long-term 

Water compatibility (scale, formation water) 

Corrosion 
Treatment required – disposal 

Corrosion  oxygenated water 

Carbon steel will corrode 

Corrosion inhibitor does not work against oxygen 

corrosion 

If water has calcium content  sulfite-based 

oxygen scavenger unusable (scale) 

Lined steel may be only option for pipeline and 

well (limits pig-ability of pipeline) 
Overview 

The water cycle 

What to analyze and analysis methods: 

— Bacteria 

— Scale 

Water compatibility

Treatment required: 

— For recycling 

— For disposal

Chemical management – impact on friction reduction 

Summary
Chemical management – impact on friction reduction

Chemical management – one example: impact on 

friction reduction 

Slickwater frac  biocide, surfactant, and friction 

reducer 

Friction reducer effectiveness: 

TDS of 150 000 mg/L not an issue; higher is 

possible 

High amount of cations not an issue with the 

friction reducer Shell uses 

Scale inhibitor ran in flow loop with frac cocktail 

result: improves friction reduction
Overview 

The water cycle 

What to analyze and analysis methods: 

— Bacteria 

— Scale 

Water compatibility

Treatment required: 

— For recycling 

— For disposal

Chemical management – impact on friction reduction 

Summary
Summary 

Proper analysis of gas, fluids, solids, and bacteria is 

key to understanding the situation 

Frac fluid composition depends on many different 

requirements  chemicals management is a must-do 

Scale inhibitor helps to recycle water, overcome 

compatibility issues, and avoids NORMs 

Disposal has to happen at one point – need to be 

prepared and understand the issues 

There is no standard solution, each field is different 

and might need a slightly different solution 

Chemistry is a key enabler to overcome the challenges 

presented 
Acknowledgements

The following people have contributed to this work: 

Shawn Baxter 

Cor Kuijvenhoven 

David Langille 

Michael Scheck 

Aurelio Zanni
Questions? 

39