## 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

### DEFINITIONS AND CAUTIONARY NOTE

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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 ) = e asy to recycle

Later flowback (produced water ): higher salinity =

m ore difficult to recycle

Recycling/Reuse : need method to recycle most of

the water b ut r ecycling water chemistry varies

Disposal : water is injected

### The water cycle – flowback vs. produced waterWater (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, Δ p 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  n eed 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 μ Sv /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 inhibitor s)

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 2055bbl/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?

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