Scaling – From Production to Reinjection3rd GNS Science - JOGMEC Workshop

Ed MroczekGNS Science Wairakei New Zealand

Tokyo10 December 2018

GNS Science

Outline2

• 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

B

A

C

D

EFG

near-neutralchloridefluids

mixing &conductive cooling

mixing &conductive cooling

hanging aquifercondensation

steam cap

boiling-point fumarolicdischarge

condensate potcold gas

seep

boilin

g oin p

tne

velop

erecharge

aquiclude

acidcondensate fluids

major convectiveupwelling

mixingrecharge

recharge

300

Co

200 Co

mixingrecharge

piezometric surface

The New Zealand Geothermal Reservoir3

B. Christenson (GNS)

• Boiling – injects CO2& H2S in

the shallow reservoir– Mixing with

oxygenated fluids– Very corrosive

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

– HClX

• Vapour Dominated– Cl in superheated vapour

• transported as HCl– concentration

• pH of the brine• temperature of

separation

X

GNS Science

The New Zealand Geothermal Acid Features4

Rotorua

Rotokawa

10B

Cl/10

10SO4

TauharaRelative B-Cl-SO4

TH1 (1964)TH1 (1967)TH2TH2 (1967)TH3 (1967)TH6TH9TH10TH11TH12TH13TH14

WairakeiRelative B-Cl-SO4

WK26BWk30Wk105Wk243Wk245Wk247

Relative B-Cl-SO4RotokawaOhaaki

Wairakei

TauharaCl/B

20

30

40

56

80

1960's

GNS Science

B

A

C

D

EFG

near-neutralchloridefluids

mixing &conductive cooling

mixing &conductive cooling

hanging aquifercondensation

steam cap

boiling-point fumarolicdischarge

condensate potcold gas

seep

boilin

g oin p

tne

velop

erecharge

aquiclude

acidcondensate fluids

major convectiveupwelling

mixingrecharge

recharge

300

Co

200 Co

mixingrecharge

piezometric surface

The New Zealand Geothermal Reservoir5

B. Christenson (GNS)

GNS Science

New Zealand Rotokawa Reservoirhighly corrosive acidic SO4-Cl rich fluids

• Rotokawa Cross Section Winick et al, 2009. NZGW

6

1 Deep upwelling reservoir fluids;

rise to shallow levels [5]

2 Clay Cap (weekly developed)

3 Central Field Fault

4 Lake Rotokawa extensive area

of acid-SO4-Cl fluids

6 Drain back downward to

generate advanced argillic

alteration in RK4/RK2

7. Boiled fluids inject large

quantities of CO2 and H2S into

steam condensates

8 Mix with oxygenated fluids

GNS Science

External Casing Corrosion of Cement Grouts7

Milestone, IRL Ltd; GRC 1990

Cement Grout Dissolution

• Ohaaki well Br23– 0.4 mol/kg H2CO3

– pH 5 @150°C• 10 months exposure

– fully carbonated all samples and cause severe corrosion

– Added quartz sample• lost over 60% of its volume

– Pure cement • 35% of its volume lost

GNS Science

L

Deep AcidityCommon 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

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

Lichti et al; NZGW 1998

GNS Science

Deep Acidity – GNS reviews9

Cl/210K

TNa/K/oC

100

150

200

250

300

350

KCl

NaCl

Dissolved Rock

• 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

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

GNS Science

Deep Acidity – Philippines 10

• 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; WGC

Ármannsson H (2012) Geochemical Aspects of Geothermal Utilization.

GNS Science

Deep Acidity – Philippines 11

• 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 of

Inconel 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

NaOH Steam Scrubbing12

• Italy, Larderello. – downhole using a capillary

and at the wellhead using corrosion-resistant wellheads,

• USA, The Geysers, California. – Superheated to wellhead– NaOH has been used

similarly– trials successful with dry

steam scrubbing using calcite packed beds and amines which avoids the reduction in steam utilization efficiency

Ármannsson H (2012) Geochemical Aspects of Geothermal Utilization.

https://docplayer.net/50647816-The-geysers-steam-purity-steam-scrubbing-process-evolution-innovationsgrc-o-m-best-practices-workshop-october-23-2016.htm

GNS Science

• Major & difficult problem – given the large volumes of brine disposed• Above

surface piping• Reinjection

Wells

Silica Scaling in New Zealand 13

GNS Science

New Zealand “Unnatural” Acidity – pH Mod 14

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0

10.0

0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

8.00

9.00

10.0

0

11.0

0

12.0

0

13.0

0

14.0

0

15.0

0

16.0

0

mls 0.01N H2SO4 added

pH

pH 6.7 (86% of acid requirement)

pH 6.2 (7% of acid requirement)

pH 5.5 (7% of acid requiremen

• 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 sponsored research (Lichti et al; WGC 2015)

• Water rock reaction of acidic fluids

• Operational and Infrastructural– Acid delivery, storage,

handling, cost Mroczek et al. WGC 2010.

GNS Science

Experimental Chemistry - Laboratory StudiesPrivate Companies (NZ & International) NEDO - GNS Corrosion studies

“real world”

“simulated world”

High Temp./Press. Apparatus400oC & 500 bar

15

GNS Science

Distance from well (m)0 20 40 60 80 100 120 140

Perm

eabi

lity

redu

ctio

n fa

ctor

0.50

0.55

0.60

0.65

0.70

0.75

0.80

0.85

0.90

0.95

1.00

Injection into of 130oC Fluid into a Reservoir at 80oC at 50 kg/s for 10 yearsAssumptions about the geometry of the porosity of the aquifer required

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

Days

0 1000 2000 3000 4000

Pres

sure

(mPa

)

5.0

5.1

5.2

5.3

5.4

5.5

5.6

with permeability reduction

without permeability reduction

Distance from well (m)

0 20 40 60 80 100 120 140

Dep

ositi

on (k

g m

-3)

0

2

4

6

8

10

12

14

16

18

20

t /oC

mg

cm-2

yea

r-1

40 60 80 100 1200

5

10

15

20

25

30

35

40

8wt% Al

6wt% Al1wt% Al

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

Scaling – Experiments and Modelling 16

GNS Science

Calcite Deposition – Production Problem

Ca++ + CO3= ↔ CaCO3

Most CO3= present as HCO3

- or H2CO3

On boiling H2CO3 → CO2

↑ + H2O2HCO3

- → CO3= + CO2

↑ + H2OOverall2HCO3

- + Ca++ → CaCO3 + CO2(g) + H2O

Calcite Scaling Thermodynamics

RETROGRADE SOLUBILITY

17

GNS Science

• Deposition Kinetics - Rapid (heterogeneous nucleation – 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 and

rapidity 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

Calcite Scaling Kinetics

Water+Steam

Water Pres

sure

incr

easi

ng

scaling

18

GNS Science

Anhydrite 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 zone

present • Antiscalant (like for calcite) effective• Often self limiting • Treat during well drilling (case off or

injecting calcium salts can work)

19

After Mubarok & Zarrouk,2017

Neutral (Calcium)

Acid-SO4

GNS Science

Iron Sulphides

• Acid fluid can carry a lot of iron from corrosion/ 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)

20

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

Jamero et al. 2018

Jamero et al. 2018 Geothermics

GNS Science

Antimony (& Arsenic) Sulphides

• 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 these conditions

• e.g. pH 5 & 15 mg/l H2S 150oC 3.34 mg/l; 100oC 0.008 mg/l

• Caustic dissolves (anion H2SbO3-)

• Antiscalants show promise (Gill, 2013)

2H3SbO3 + 3H2S = Sb2S3 + 6H2O

21

GNS solubility experiments (Olsen et al 2018)

GNS Science

• Keep the scaling in the wellbore• Maintain WHP and control output

NZ Calcite Scaling Management

0.1 mg/l Ca

0.25 g/tonne CaCO3

300 275 250 225 200 175 150t/ oC

-3

-2

-1

0

1

2

3

Log

Q/K

BR56BR59BR61

1 Step Flash

Paul Bixley

scaled liner

22

0 0.05 0.1 0.15 0.2 0.25g calcite/tonne flow

1800

1600

1400

1200

1000

800

Casin

g de

pth/

m

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

GNS Science

• Antiscalant injection • Highly effective• Below boiling point• Many commercially available• Need to choose appropriate

one (lab and field testing)• Not out in the formation

NZ Calcite Scaling Management 23

GNS Science

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)

24

Broaching Tool

Rig

What is more expensive Avoidance or workovers ?

GNS Science

Geo40 (New Zealand) Manufacture of colloidal silica

Ohaaki Commercial Demonstration Plant (in co-operation with Contact Energy Ltd and Ngati Tahu Tribal Lands)

25

GNS Science

Conclusions

Scaling occurs from Production to Reinjection. It cannot be totally avoided.

However thorough chemical understanding of the influent and effluent 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 potential for disaster.

26

GNS Science

Acknowledgements

GNS ScienceContact Energy LtdMercury Energy LtdWairakei Prawn park New Zealand Government Research Funding