Water Treament

How is Silica removed?

Along with the precipitated Magnesium Hydroxide, Mg(OH)₂

• The silica is removed from the water through electrostatic adsorption onto the surface of the Mg(OH)₂ precipitate

  • Mg(OH)₂ forms as MagOx is added as a dry chem at the top of the WLS

How can more Mg(OH)₂ be added?

By adding MgO (Magnesium Oxide - aka MagOx) that then forms Mg(OH)₂ upon contact with water

What is hard water?

Water that contains a lot of dissolved ions → particularly Mg⁺² and Ca⁺²

Why does water become hard?

Water is a strong solvent

• It picks up minerals as it moves through rock

  • Produced water has been in contact with the formation for millions of years - amplifying its hardness compared to typical groundwater

Why is water hardness a problem in SAGD operations?

The SPF is essentially a steam factory

• hard water causes efficiency and mechanical problems for steam generators

What are the 3 main functions/processes in a SAGD CPF

1. Treat the produced emulsion

   • ie. separate the oil, water, and gas

2. Treat the produced water

   • Reduce hardness

3. Generate steam for injection

Water treatment is a balancing act between __________ and _________

corrosion and scale control

Why is hardness a problem in SAGD SPFs?

Because hardness causes severe scale in in steam generators

• The magnesium and calcium ions precipitate as scale in boilers and exchangers

  • This scale reduces the efficiency and shortens the life of the equipment used in steam generation (ie. boilers - BFW)

Hardness also damages the heat transfer equipment, which requires downtime for acid cleaning

• Heat exchangers

• Produced water coolers

Name 3 types of common SAGD scale minerals

• CaCO₃ → carbonate

• CaSO₄→ anhydrite

• Calcium-magnesium-silicates

What are the 3 main methods of reducing water hardness at Christina Lake?

• WLS → Warm Lime Softening

  • Bulk removal (80-90% of the load)

  • Solids settle as sludge and are physically removed

• WAC → Weak Acid Cation exchange

  • removes hardness associated with alkalinity (bicarbonate hardness)

• SAC → Strong Acid Cation exchange

  • removes permanent hardness

    • removes remaining Ca²⁺ and Mg²⁺

    • final polishing before boilers

What is the difference between temporary and permanent hardness?

Temporary → carbonate hardness → caused by magnesium and calcium bicarbonates dissolved in water

• Ca(HCO₃)₂

• Mg(HCO₃)₂

• temporary because it can be removed by lime addition (WLS)

• WLS + WAC

Permanent → non-carbonate hardness → caused by sulfates, nitrates or chlorides of calcium and magnesium that cannot be removed by lime addition (WLS)

• CaSO₄

• MgSO₄

• CaCl₂

• MgCl₂

• SAC

What is the device used to measure turbidity?

Nephelometer

• measures tubidity in units of NTU → Nephelometric Turbidity Units

What is alkalinity?

A measure of the water’s ability to neutralize acids

• depends mainly on the amount of bicarbonate present

• Too high → scale deposits can form

• Too low → corrosion

Scale formation rate ______ with increasing pH

increases

What do the following acronymns stand for?

• CPF

• WLS

• WAC

• SAC

• BFW

• CPF → Central processing facility

• WLS → Warm lime softening

• WAC → Weak acid cation exchange

• SAC → Strong acid cation exchange

• BFW → Boiler feed water

• WRU → Water recovery unit

What is the skim tank used for?

Removes free and weakly emulsified oil from the produced water before it continues on for treatment

• Situated after the FWKO and Treaters

• Before WLS

What are the main processes in HLS?

• Deaeration to remove CO₂ and Oxygen

• Induce precipitation reactions

• Silica reduction

• Clarification

What are the 3 main chemicals used by SLB at the CPF?

• Emulsion Breaker (EMBR 10070A)

• Coagulent (CLAR 18114A)

• Flocculent (CLAR 01601A)

What is the purpose of EMBR 10070A and where is it used at the plant?

It is used to break emulsions in the emulsion line feeding the plant

• Added into the line at loop stations to the north of the plant

What is the purpose of CLAR 01601A and where is it used at the plant?

Flocculent

• Used to bind the destabilized particles into large, dense flocs that settle

• Added at the spray box on the WLS

What is the purpose of CLAR 18114A and where is it used at the plant?

Coagulent

• Used to destabilize the suspended particles by neutralizing the surface charge on them

  • Once particles are neutralized they can collide and stick together (ie. coagulate)

What is sludge recirculation used for in the WLS?

Provides seeds to increase precipitation

• These recirculated solid particles provide a surface for the hardness ions to attach to

  • This improves floc size and settling rates

What is the process for checking Treater taps?

1. Open sample line

2. Open by-pass/slop line

3. Open the tap you want to check

4. Go to hood and open valve to check tap

5. Find CW and label with clip or magnet

Describe the chemicals used in WLS

Into the top → lime, magox, soda ash (dry chems)

Inlet produced water stream → Coagulent (CLAR 18114A)

Fed into spray box → Flocculant (CLAR 01601A)

What is the primary role of lime in WLS?

Alkalizing agent that forces precipitation of temporary hardness

What is the primary purpose of magox (MgO) in WLS?

Reduction of silica

Where is the OIW concentration evaluated?

• Describe the process

Off the water dump line of the FWKOs and treaters

1. Take 2 50ml samples of water off the dump line

2. Add 2 pumps of acid to one and shake

3. Add 50ml Varsol to each

4. Shake both and compare colour of Varsol

   • Darker = more residual hydrocarbons = higher ppm

Describe the process of testing sales oil and FWKO oil

Purpose → shows treater performance by testing BS&W before and after the treater

1. Collect a samples from the FWKO outlet and the sales line

2. Bring to oil lab

   • In centrifuge tubes add Varsol to 100 and then the oil to 200 for both samples

   • Place in the centrifuge on opposite ends (to counter-balance)

   • Spin for 10mins and read the BS&W

What can happen if too much floc or coag is added in WLS?

You will overcharge the particles and they will repel eachother

What is the name of the cones used when testing the taps on the WLS?

Imhoff Cones

Describe the process of testing the taps on the WLS units

1. Fill your cones to 100 and start the stop watch

2. After 10mins take the sludge % reading from each cone

What is meant by carryover?

An unwanted substance being carried past where it should have been removed.

• ie. oil carryover from a treater