1st Combined Network Meeting on Modelling and

Wellbore Integrity, Perth Australia, April 27-29, 2 011

Cementing Strategies for Effective Zonal Isolation of CO 2 Wells

Andreas Brandl (Baker Hughes)Scott Bray (Baker Hughes)

Christina Magelky (Baker Hughes) Ragheb Dajani (Hess Corporation)

OVERVIEW

• Review: Zonal Isolation of CO2 wells (field studies)

What can we do ‘in addition’ to prevent leakage?

• Sealing Spacer improves cement placement

• Expanding cement system supporting bond

• CO2 tolerable cement for long term bond

RESULTS FROM FIELD STUDIES

• Portland cement degradation due to CO2: <10 mm / 30 yrs (J.W. Carey et al. 2007)

• Degradation mainly occurs along existing / induced pathways (B. Kutchko et al. 2009)

• Pozz/Portland cement inhibit CO2 migration after carbonation (W. Crow et al. 2009)

⇒ Leakage only due to CO2 attack very unlikely

⇒ Cements ability to resist CO2 attack is secondary

⇒ Important: Good initial cement bond

OVERVIEW

• Review: Zonal Isolation of CO2 wells (field studies)

What can we do ‘in addition’ to prevent leakage?

1. Sealing Spacer improves cement placement

2. Expanding cement system supporting bond

3. CO2 tolerable cement for long term bond

SEALING SPACER - PURPOSE

Reducing lost circulation problems & damages

• Permeable, fragile, and weak formations

• (Natural) fractures

• Depleted reservoirs

Strengthening wellbore & Allowing cement placement

• Low frac gradients

• Narrow ECD margins (limit cement density)

SEALING SPACER - BENEFITS

Sealing

Typical Spacer

applied prior cementing

Sealing Spacer

applied prior cementing

• Prevents formation breakdown & fall back of cement tops• Strengthens wellbore for improved cement slurry placement

STRENGTHENING OF WELLBORE

Before Sealing Spacer was applied:• Cementing required a stage tool, since desired height exceeded max. ECD of 10.93 ppg

After using Sealing Spacer:• Cementing in single stage at ECD 12.26 ppg• No losses, top of cement found at desired top

=> Operator saved time & money with a high quality cement job

SEALING SPACER’s EFFICIENCY

Sealing Spacer

Typical Spacer

No flow

Blow

out

No losses when Sealing Spacer is applied

20/40

frac sand

MORE BENEFITS OF THE SEALING

CO2

Mg2+

H2S

Sealing

SO42-

• Sealing acts like a “condom”• Potentially protects cement sheath towards corrosive fluids

OVERVIEW

• Review: Zonal Isolation of CO2 wells (field studies)

What can we do ‘in addition’ to prevent leakage?

1. Sealing Spacer improves cement placement

2. Expanding cement system supporting bond

3. CO2 tolerable cement for long term bond

Expansion and Shrinkage Under Temperature and Pressure

• Patented BHI Molds (US 6,918,292)• Placed in a modified HTHP curing chamber • Measures shrinkage & expansion real time• SPE/IADC 79911

Cement Additives for ExpansionLeft Sample: Class G cement + 0.75% EC-2 + 35% S-8 + 0.8% FL-25 + 0.6% CD-32 + 0.5% R-

8 mixed at 16.7 ppg, Yield = 1.40 cu ft/sk, and Fre sh water = 5.06 gal/sk

-0.3

-0.25

-0.2

-0.15

-0.1

-0.05

0

0.05

0.1

0.15

0 20 40 60 80 100 120 140 160Elapsed Time (hr)

% L

ine

ar

Exp

ans

ion

or S

hrin

kage

0

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

Te

st T

em

pera

ture

(°F

) a

nd P

ress

ure

(ps

i)

Test Temperature

Test Pressure

% linear Expansion

Base-Line

The Cement was heated in 4:00 hrs to its final (BHST) Temperature and Pressure. After 4 hrs, the temp and pres has estabil ized. Any test data above the base-line are consider expansion and below are shrinkage.

Right Sample: Class G cement + 35% S-8 + 5.0% EC-2 + 0.8% FL-25 + 0.6% CD-32 + 0.5% R-8 mixed at 16.7 ppg, Yield = 1.40 cu ft/sk and fres h water = 5.02 gal/sk

-2

0

2

4

6

8

10

12

0 5 10 15 20 25 30 35 40 45 50

Elapsed Time (hr)

% L

ine

ar

Exp

ans

ion

or S

hrin

kage

0

500

1000

1500

2000

2500

3000

3500

4000

Te

st P

ress

ure

(psi

) a

nd T

em

pera

ture

(°F)

% Linear Expansion

Test Temperature

Test Pressure

Out of ranges (expansion device)

Base-line

The cement was heated in 4 hrs to its final (BHST) temperature and pressure. After 4 hrs, the temp and pres has estabil ized. Any test data above the base-line are consider expansion and below are shrinkage.

Delayed hydration of MgO

+ Expansion after cement set

- Overdosage → cracking

Cement Additives for Expansion

Metallic aluminum powder as gas generator

- produces H2 gas in alkaline environment

- difficult to control

- gas generation occurs prior cement setting

Metallic aluminum powder as gas generator

- produces H2 gas in alkaline environment (safety issue)

- difficult to control expansion

- gas generation occurs prior cement setting

Expanding Cement System

+ 13.3 – 15.8 ppg

+ HT polymeric extender

+ Stable @ 465 F

+ No gas generation

+ No shrinkage

+ Controlled Expansion

→ Supports bond

→ Reduces micro annuli

→ Field proven technology (SPE ATC 147012)

OVERVIEW

• Review: Zonal Isolation of CO2 wells (field studies)

What can we do ‘in addition’ to prevent leakage?

1. Sealing Spacer improves cement placement

2. Expanding cement system supporting bond

3. CO2 tolerable cement for long term bond

CO2 Attack in API Cement

I. unaltered set cement

III. carbonated cement

IV. porous silica (soft)

CO2 +

H2O ⇌⇌⇌⇌

H2CO3 ⇌⇌⇌⇌

H+ +

HCO3-

V. corrosive fluid

Leaching frontCarbonation front

C-S-H phases

Ca(OH)2

dissolve

Ca2+aq

OH-aq

precipitates dissolves

Ca2+aq

H+aq

HCO3-aq

CaCO3

SPE 132228-PA

After 6 Months Exposure to CO 2

Cement specimen flaked off (diameter ∆=-0.6 mm)Cement bond failure / migration pathways => Loss of zonal isolation

CO2 tolerable cement Conventional

Exposed to 1 M HCl (24 hrs)

2 H+ + Ca(OH)2 Ca2+ + 2 H2O

12 H+ + C6-S5-H6 6 Ca2+ + 5 SiO2 + 6 H2O

CO2 tolerable cement Conventional

Simulate: final of leaching step during CO2 exposure

-60%

-50%

-40%

-30%

-20%

-10%

0%

0 50 100 150 200 250 300

Exposure time to 1 molar hydrochloric acid (days)

Loss

of m

ass

(wt%

)

pozzolan

conventional

Durability in 1 M HCl (250 d)

Conventional

CO2 tolerable cement

After 250 d Exposure to 1 M HCl

EDS analyses confirm complete Ca leaching for both

ConventionalCO2 tolerable cement

Conventional

C.S.= 1,520 psiW.P.= 0.00123 mD

• fell apart• no strength• squishy morph.

Durability in 1 M HCl (250 d)

CO2 tolerable cement

Long Term Zonal Isolation0. Seal & Strengthen Formation

1. Follow good practices with API cement based systems (reliable, field proven & practical)

2. Improved cement bonding

3. Design a cement system:• with suitable mechanical properties • preventing strength retrogression• mitigating all corrosive attacks (Mg2+, SO4

2-, H2S, CO2 …)

∆P

∆T

CO2

Thank You for Your Interest

PERTH, AUSTRALIA