Scaling – From Production to Reinjection
3rd GNS Science - JOGMEC Workshop

Ed Mroczek
GNS ScienceWairakei
New ZealandTokyo
10 December 2018

2Outline•••
••••
•
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The New Zealand geothermal reservoir
Rotokawa reservoir
ECC cement grout
Deep Acidity Examples and Management
Silica Scaling
Calcite Scaling
Anhydrite Scaling
Iron sulphides
Antimony sulphide (stibnite)
Silica and Calcite Scaling Management

GNS Science

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The New Zealand Geothermal Reservoir– concentration• pH of the brine• temperature ofseparation•boiling-point fumarolicdischarge

EFsteam cap Dcondensation

aquiclude

hanging aquifer

piezometric surface

Crecharge
nrecharge

BeCto020oinX
X• transported as HCl

G

condensate
pot

gp

Vapour Dominated– Cl in superheated vapour

cold gas
seep

acid
condensate
fluidsilin•

Boiling– injects CO2& H2S inthe shallow reservoir– Mixing withoxygenated fluids– Very corrosivebo•

mixing &conductive cooling

Deep Acidity - Magmatic Fluids– 4SO2 → H2S + 3H2SO4– HClomixing

near-neutral
chloride
fluids

A030

recharge

pelovemixing &conductive cooling

Cmajor convective
upwelling

mixingB. Christenson (GNS)

recharge

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The New Zealand Geothermal Acid Features

Rotorua
TauharaRelative B-Cl-SO4
TH1 (1964)
TH1 (1967)
TH2
TH2 (1967)
TH3 (1967)
TH6
TH9
TH10
TH11
TH12
TH13
TH14

Wairakei
Relative B-Cl-SO4
WK26B
Wk30
Wk105
Wk243
Wk245
Wk247

Cl/10

Relative B-Cl-SO4
Rotokawa
Ohaaki

Wairakei

Rotokawa

80

Cl/B
1960'sTauhara

56
40
30
20

10SO4

10B

GNS Science

5The New Zealand Geothermal Reservoir
cold gas
seepG

condensate
potacidcondensate
fluidsboiling-point fumarolicdischargeEF

steam cap D

condensation

aquiclude

hanging aquifer

piezometric surface

Crechargenrecharge

toin
ilin
boBeC

gpo

020

mixing &conductive coolingomixing

near-neutral
chloridefluids

A

030

recharge

pelovemixing &conductive cooling

Cmajor convective
upwellingmixing

B. Christenson (GNS)

recharge

GNS Science6

New Zealand Rotokawa Reservoir
highly corrosive acidic SO4-Cl rich fluids
1 Deep upwelling reservoir fluids;
rise to shallow levels [5]2 Clay Cap (weekly developed)
3 Central Field Fault
4 Lake Rotokawa extensive areaof acid-SO4-Cl fluids
6 Drain back downward togenerate advanced argillicalteration in RK4/RK2
7. Boiled fluids inject large
quantities of CO2 and H2S intosteam condensates• Rotokawa Cross Section Winick et al, 2009. NZGW

8 Mix with oxygenated fluids

GNS Science7External Casing Corrosion of Cement Grouts••Ohaaki well Br23
– 0.4 mol/kg H2CO3– pH 5 @150°C
10 months exposure– fully carbonated all samples andcause severe corrosion– Added quartz sample• lost over 60% of its volume– Pure cement

Cement Grout Dissolution

Milestone, IRL Ltd; GRC 1990

• 35% of its volume lostGNS Science•

Deep Acidity
Common in Many Volcanic Geothermal Fields

8

Not all acid is created equal!
HSO4/SO4 & CO2/HCO3 Buffers
SO4/HSO4/ & CO2/HCO3 Buffers– pH at depth is neutral– Acidity increases markedly at shallow depth– Well bore corrosion

L• HCl– Completely dissociated– Low pH in reservoir and at shallow depths

Lichti et al; NZGW 1998

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Deep Acidity – GNS reviews•Mt Apo; Philippines– pH 3.2-5.5– Cl-Na-K relative
proportions– No excess Cl– Acidity due to SO4– Silica• 1000 mg/L
• No deleterious scaling• Little pipe corrosion• Amorphous silica
protects from corrosion

100150TNa/K/oC
200
NaCl

250

300
350

Dissolved Rock10KCl/2

KCl

Nogara et al. 27 Workshop on Geothermal Reservoir Engineering, 2002

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Deep Acidity – Philippines•Mt Apo;– Now lower pH 2.5– Corrosion observed– pH too low for Am Silica protection– NaOH injection trial• pH to 4.5– Not successful• Mahanagdong– pH 2.87 - 4.05
– NaOH solution through a 1″
Incoloy 825 tubing at 20 m depth– Thinning rate decline•

1.05 to 0.21 mm day−1– corrosion control pH of 4.5

Tamboboy et al. 2015; WGCÁrmannsson H (2012) Geochemical
Aspects of Geothermal Utilization.
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Deep Acidity – Philippines•Tiwi– The production liner was removed and the corrosive zones isolated– injection of 4 wt.% NaOH at a depth of 1070 m (12.7 mm capillary tubing ofInconel 625.
– The pH is controlled at 4.5–5.0.
– Overdosing with NaOH (pH > 6) is found to exacerbate silica scaling– Dissolved iron concentrations in the fluid have been reduced by 80%Ármannsson H (2012) Geochemical
Aspects of Geothermal Utilization.

GNS Science12NaOH Steam Scrubbing••

Italy, Larderello.
– downhole using a capillary
and at the wellhead using
corrosion-resistantwellheads,USA, The Geysers, California.
– Superheated to wellhead– NaOH has been usedsimilarly– trials successful with dry
steam scrubbing using
calcite packed beds andamines which avoids thereduction in steam utilization
efficiency

Ármannsson H (2012) Geochemical Aspects of Geothermal
Utilization.

https://docplayer.net/50647816-The-geysers-steampurity-steam-scrubbing-process-evolution-innovations
grc-o-m-best-practices-workshop-october-23-2016.htm
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Silica Scaling in New Zealand• Major & difficult
problem – given
the large
volumes of brine
disposed• Abovesurface piping• Reinjection
Wells
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New Zealand “Unnatural” Acidity – pH Mod

pH 6.7 (86% of acid requirement)
10.0

pH 6.2 (7% of acid requirement)

9.0
8.0
7.0

pH 5.5 (7% of acid requiremen

6.0
5.04.03.0
2.0

mls 0.01N H2SO4 added

Mroczek et al. WGC 2010.

GNS Science

16.00

15.00

14.00

13.00

12.00

11.00

10.00

9.00

8.00

7.00

6.00

5.00

4.00

3.00

2.00

0.0

1.00

1.0

0.00

Control of silica scaling– H2SO4 dosing– 3 NZ Geothermal fields• Including Rotokawa !
– Difficult process to control• Adding acid
• Corrosion pH 5.5 (@25°C• Heavy metal (Sb & As) causing
corrosion on Fe pipes (Quest
Integrity GNS sponsoredresearch (Lichti et al; WGC 2015)• Water rock reaction of acidicfluids• Operational and Infrastructural– Acid delivery, storage,handling, costpH•Experimental Chemistry - Laboratory Studies
Private Companies (NZ & International)
NEDO - GNS Corrosion studies

15

High Temp./Press. Apparatus
400oC & 500 bar“realworld”“simulatedworld”

GNS ScienceScaling – Experiments and Modelling

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With silica deposition rate data we can calculate
the effect of scaling in the reinjection aquifer !

1.00

350.95mg cm-2 year-130
25
20
15
106wt% Al
1wt% Al
8wt% Al50406080

100Permeability reduction factor

400.900.850.800.75
0.70
0.65
0.60
0.55
0.50

120

0t /oC

20406080 100 120 140

Distance from well (m)

20

5.6
5.5

16

Pressure (mPa)

Deposition (kg m-3)

1814121086

5.4

with permeability reduction

5.3
5.2
without permeability reduction

4

5.1

20

5.0

0

20

4060

80 100 120 140

Distance from well (m)

01000

2000

3000

4000

Geochimica, 1998; NZGW 1997, 1999;
Geothermics 2000.

Days

Injection into of 130oC Fluid into a Reservoir at 80oC at 50 kg/s for 10 years
Assumptions about the geometry of the porosity of the aquifer required
GNS Science17Calcite Scaling Thermodynamics
Calcite Deposition – Production Problem
Ca++ + CO3= ↔ CaCO3
Most CO3= present as HCO3- or H2CO3On boiling
H2CO3 → CO2↑ + H2O
2HCO3- → CO3= + CO2↑ + H2O
Overall
2HCO3- + Ca++ → CaCO3 + CO2(g) + H2O

RETROGRADE SOLUBILITYGNS Science18•
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Deposition Kinetics - Rapid (heterogeneousnucleation – seed available)
Occurs within wellbore just above flash point
Scaling calibrated for the field Some wells predicted to scale but don’t Depends on how the boiling occurs andrapidity of depressurization
Severe scaling can results out in the formation
 Cannot remediate easily
Surface Pipes• Mixing of incompatible fluids (high HCO3and high Ca• Degassing due to depressurization

Water+Steamscaling

Water

Pressure increasing

Calcite Scaling Kinetics

GNS Science19Anhydrite Scaling
Ca2+ + SO4= = CaSO4
Caused by mixing Ca and SO4 fluids
Independent of pH
Retrograde solubility
Not common in production wells
Mainly volcanic geothermal
environments• But often shallow acid-sulphate zonepresent• Antiscalant (like for calcite) effective• Often self limiting• Treat during well drilling (case off orinjecting calcium salts can work)
••••
•
•

AcidSO4

Neutral(Calcium)

After Mubarok & Zarrouk,2017

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Iron Sulphides
Pyrite FeS2; Pyrrhotite Fe(1-x)S (x = 0 to 0.2)

• Acid fluid can carry a lot of iron fromcorrosion/ erosion• Precipitates in response to boiling &cooling- sensitive to pH and H2S & H2
gas fugacity (redox)• Severe problem can occur- when mixing incompatible fluids(low and high pH, high iron, gas, differing enthalpy)

Jamero et al. 2018

Jamero et al. 2018 Geothermics

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Antimony (& Arsenic) Sulphides
2H3SbO3 + 3H2S = Sb2S3 + 6H2O

• Particular problem in NZ
Geothermal Fields (Brown, 2011)• Now reported elsewhere• Binary Plants• pH mod for silica inhibition• Low pH and cool temperatures
required• Highly insoluble under theseconditions• e.g. pH 5 & 15 mg/l H2S 150oC
3.34 mg/l; 100oC 0.008 mg/l
• Caustic dissolves (anionH2SbO3-)• Antiscalants show promise (Gill,2013)
GNS solubility experiments (Olsen et al 2018)

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NZ Calcite Scaling Management• Keep the scaling in the wellbore• Maintain WHP and control output
0.1 mg/l Ca

800

0.25 g/tonne CaCO31000

31 Step Flash

Casing depth/m

2Log Q/K

10-1

BR56
BR59
BR61

-2

1200

1400

1600

scaled liner

After Brown (UNU-GTP-2013-39,2013)

1800

-3
300

275

250

225t/ oC

200

175

150

00.05

0.1

0.15

0.2

0.25

g calcite/tonne flow

Paul Bixley
GNS Science23

NZ Calcite Scaling Management• Antiscalant injection• Highly effective• Below boiling point• Many commercially available• Need to choose appropriate
one (lab and field testing)• Not out in the formation

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NZ Scaling Management – calcite & silica• Periodic Well Workovers• Reaming• Acidizing (implications for well integrity!)– HCl & HF
• High pressure water blasting• Broaching• Novel Chemical treatment (Alkali, EDTA)

What is more expensive Avoidance or workovers ?

RigBroaching Tool
GNS Science25

Geo40 (New Zealand)
Manufacture of colloidal silica
Ohaaki Commercial Demonstration Plant (in co-operation with Contact
Energy Ltd and Ngati Tahu Tribal Lands)

GNS Science26Conclusions
Scaling occurs from Production to Reinjection.
It cannot be totally avoided.
However thorough chemical understanding of the influent andeffluent composition and chemistry, good power station design,monitoring of the reservoir response to production and knowledge
on how to deal with the problem all work to minimizes the potentialfor disaster.

GNS ScienceAcknowledgements

GNS Science
Contact Energy Ltd
Mercury Energy Ltd
Wairakei Prawn park
New Zealand Government Research Funding

GNS Science