1

Wellbore Cements Durability Under Geological Sequestration Conditions

MILEVA RADONJIC Tevfik Yalcinkaya,

Nnamdi Agbasimalo, Abiola Olabode, Tao Tao & Dinara Dussenova

LOUISIANA STATE UNIVERSITY

mileva@lsu.edu

RECS 2011, Birmingham, AL – June 8

1

Outline Cements 101

Cement chemistry Cement hydration

Cement microstructures

Well Cementing Well design

Well cement role

Well Cements Deterioration Field vs Lab examples

Cement/Casing Interface Cement/Formation Interface

Conclusion

2

Range of length scales in subsurface engineering – applications for CCS

From Tyagi and Thompson, LSU

Sub-pore scale Pore scale Core-plug scale Wellbore scale Reservoir scale

Length scale (m)

103 – 10?? 10-7 – 10-4 10-4 – 10-2 10-2 - 103 10-9 – 10-6

Ref: Deepwater Horizon Accident Investigation Report Appendix W

3

Capacity- Injectivity - Containment

4 Time line: Containment – Trapping - Risk

https://ww

w.crc.gov.au/Inform

ation/default.aspx)

1.  CO2 must remain trapped over extended time periods 2.  In the injection period, trapping is only provided by

physical barrier systems such as CAP-ROCK and WELLBORE CEMENT.

Abandoned wells

Injection wells

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•  More than 8,000 wells in the GOM have sustained casing pressure. (U.S. Federal Register, 2010)

•  14,477 wells out of the 316,439 wells in Alberta, Canada are leaking. (Watson & Bachu, 2009)

•  CO2 sequestration cannot be carried out in the presence of leaky wells.

What we know from O&G

Pre-production •  Inadequate drilling mud removal •  Incomplete cementing due to casing eccentricity •  Cement shrinkage and casing contraction •  Contamination of cement by various wellbore fluids During Production •  Mechanical stress/strain due to changes in pressure and temperature

leading to - formation of micro-annulus at the casing-cement interface

- formation of micro-annulus at the cement-formation interface - development of fracture network in the cement

•  Geochemical attack – Acid and sulfate attack leading to degradation of cement and corrosion of casing

Wellbore leakage is caused by the following:

4

Rock

 Cement      Sheath  

Wellbore  Cement    

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•  Risk assessment of abandoned wells prior to implementation.

•  Wellbore cement is the key for ensuring wellbore integrity over extended period of time. Production

Casing

Intermediate Casing

Evaluate interaction between fractures inside cement sheath and acidic brine .

Main functions of wellbore cements are:

1.  ZONAL ISOLATION 2.  STRUCTURAL SUPPORT 3.  CASING PROTECTION

Fracture

Potential Pathways for Wellbore Leakage

•  Leakage occurs at microscale

•  Integrated measures are necessary for large-scale models

5

The impact of micro-properties of hydrated cement paste on its durability in a chemical

environment

•  Composition –  (mix-design, hydration level,P/T)

•  Microstructure –  (morphology, texture, porosity)

•  Physical integrity –  (microcracks)

• Permeability

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Hydra2on  of  Cement      

Four stages of hydration in a microstructural model of C3S hydration (Garboczi, nist.org) The degrees of hydration: top left--0, top right--20 %, bottom left--50%, bottom right--87%. Red=unreacted cement, blue=CH, Yellow=C-S-H, Black= macroporosity.

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11

Hydrated  Cement  Conduc2vity      

Sources: Cement Chemistry, H.W. Taylor, 1996)

Shift in Pore structure

•  Hydration is 70% complete in the first 28 days

•  C-S-H makes up to 70% , CH up to 20%

•  Water/cement ~ 0.4

has 25% to 35% porosity

•  Capillary pores and gel pores (bellow 0.01 µm)

•  Time effect on the cement microstructure

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•  pH of cement pore water is ~ 13-14, (highly alkaline)

•  CO2 dissolved in formation water results in pH lower than 7

•  Wellbore cement not compatible with an acidic solution

•  How fast cement will deteriorate depends on several parameters (permeability, flow rate, chemistry, stresses..).

Cement  Chemistry    

Source: Applications of Environmental Aquatic Chemistry, Weiner E

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Tea Pot Dome 19yrs old cement well cement 1 well cement 3a

Tea Pot Dome well cement 1

BSE & EDS

Ca

Ca Ca

Ca

Ca

Ca

Ca

Si

Si

Si

Si

Si

Si Si

Al

Al

Al

Al Al

Fe

Fe Fe

Fe

Ti Ti

Ti

S S

S

S

O

O

O

O O

O O

Mg

Mg

Mg Mg Al

Cl

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SHALE – CEMENT AFTER YEARS OF CONTACT WITH CO2

9

Optical image of a porous opening in the SFZ showing a boxwork texture.

1mm

Source: Carey et al, 2006

Polished slab showing orange zone with gray cement on the left and Shale Fragmented Zone on the right.

Adapted from Carey et al, 2006

Gray cement

Orange zone SFZ

X-ray EPMA maps (WDS): cement osteoporosis spatial elemental distribution across reacted-cement sample

Ca

S Fe

Si

1

1

1

1

2

2

2

2

3

3

3 cc ACIDIC

BRINE

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Laboratory Set-Up & Sample Prep 19

12 in

1 in

Fracture Width (w)=0.6 in Aperture Size (b)

Fracture length, L=12 in

Single Fracture Geometry Regions of Interest

Hassler Holder

Syringe Pump Cement Core (1 in by 12 in)

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X-­‐Ray  Computed  Tomography  (Low  Resolu2on  CT)

•  The un-reacted and reacted cement cores were scanned at 8 different locations along the core from bottom to top in order to nondestructively visualize the alterations along 12 in core.

Inlet

Outlet

Inlet

Slic

e #1

Sl

ice

#7

Unreacted Reacted

7

8

7

Unreacted Reacted

Low    Pressure    Experim

ent

8

Outlet

•  Visible increase in fracture aperture.

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21

⎥⎥⎦

⎤

⎢⎢⎣

⎡ Δ×=

µlbpwQ3

10611.5Days   Pressure Drop

Data  Aperture  

control   5.6 psi   57.2 µm  

1   5.6 psi   57.2 µm  7   7 psi   53 µm  

14   8 psi   50.8 µm  21   5.2 psi   58.6 µm  28   4.9 psi   59.6 µm  30   5 psi   59.4 µm  

Unconfined Stress conditions

Confined Stress conditions (600 psi)

4% Widening

Average ~ 24.5%

Widening

Std. Deviation ~ 8.5%

Fracture  Aperture  Measurements/Calcula2ons

Measured Values

Calculated Values

Axial Slice#   Aperture, unreacted  

Aperture, reacted  

1 (outlet)   0.71 mm   0.90 mm  2*   0.59 mm*   0.81 mm  3   0.97 mm   1.06 mm  4   1.15 mm   1.34 mm  5   1.05 mm   1.35 mm  6   0.85 mm   1.04 mm  7   0.72 mm   0.91 mm  

8 (inlet)   0.79 mm   1.04 mm  

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Reacted core-Top view LP, low

magnification Two regions

3 mm 0.1 mm

Ca/Si  is  5.64  for    Unreacted  core  

Ca/Si ~4

Ca/Si ~ 42

Ca/Si ~ 13

Reacted core-Top view LP, medium

magnification Partial fracture

healing

Reacted core-Top view LP, high magnification Calcite growth

within the fracture

ESEM & EDS

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Unhydrated cement

Altered cement Secondary micro fractures/oriented growth parallel and perpendicular to the observed primary fracture

Identification of spatial distribution of phases and pore/fracture detection Brighter color-higher atomic mass

ESEM EBS 23

Bridging

Crystal growth within fracture 24

13

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Calcite-black arrow

Dissolution-red arrow

Intact cement- white arrow

Element   Wt %   At %   C K   04.13   07.42   O K   50.27   67.81   SiK   02.38   01.83   CaK   41.02   22.09   FeK   02.21   00.85  

Reaction products at the fracture wall

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Outlet

Outlet

Inlet

I  

II

Fracture Surface

Inner Part

Cross sectional view of LP Experiment Micro-CT along xy/ Axial Slices-30days

Micro-CT Images: Different Orientations

I

II  

LP Experiment Micro-CT along xz (H=5mm)

HP xz (H=3mm) HP Experiment Micro-CT along xy/ Axial Slices-10days

Fracture Surface

Inner Part

Transition

Transition

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Outlet

Inlet

I  

II

Time Effect clearly visible when comparing 4 weeks to 12weeks experimental data: extensive fracturing and loss of solid/increased porosity/permeability, compromised overall integrity of cement matrix.

Inlet Outlet LP Experiment Micro-CT along xy/ Axial Slices

Micro-CT Images: Different Orientations at 100days

Fracture Surface

LP Experiment Micro-CT along xz (H=5mm)

Inner Part

Fracture Surface

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0

0.001

0.002

0.003

0.004

0.005

1 10 100

Cum

ulat

ive

Intr

usio

n (m

L/g)

Pore radius (µm)

Reacted LP_7-8 Unreacted LP LP Reacted_1-2 Unreacted HP Reacted HP

0

0.02

0.04

0.06

0.08

0.1

0.12

0.001 0.01 0.1 1

Cum

ulat

ive

Intr

usio

n (m

L/g)

Pore radius (µm)

Reacted LP_7-8 Unreacted LP LP Reacted_1-2 Unreacted HP Reacted HP

HP porosity increase

LAR

GE

P

OR

ES

S

MA

LL

PO

RE

S

LP porosity different at inlet(-) and outlet(+)

Mercury Intrusion Porosimetry

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29 Induc2vely  Coupled  Plasma  (ICP)  #Days  

Ca2+ (mg/L)   Effluent pH   mf   pf  

HCO3-

(mg/L)  CO3

-2 (mg/L)  

OH-

(mg/L)  

Control Sample   0.48   4.7   0.22   0   134.2   0   0  

0   39.40   5.9   0.56   0   341.6   0   0  6   16.65   6.9   0.23   0   140.3   0   0  

12   14.83   6.8   0.12   0   73.2   0   0  15   12.69   9.5   0.42   0.11   122   66   0  

18   18.05   10.2   0.17   0.06   30.5   36   0  

21   11.55   9.6   0.22   0.01   122   6   0  

24   11.51   9.3   0.15   0.02   67.1   12   0  27   11.28   6.5   0.24   0   146.4   0   0  

30   20.05   10.1   0.25   0.13   0   72   1.7  

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Saturation index (SI)= log (IAP)-log (Equilibrium Constant)

Ion activity product (IAP)= (activity of Ca) * (activity of CO3-2 )

Under-saturated to oversaturated -6

-5

-4

-3

-2

-1

0

1

2

0 5 10 15 20 25 30 35

Satu

ratio

n In

dex

(SI)

Time (Days)

dissolution

equilibrium precipitation

dissolution

Equilibrium precipitation

dissolution

Equilibrium precipitation

SI>0, solution is over-saturated with calcite

SI<0, solution is under-saturated with calcite

Saturation Index Calculations

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0   0.08  mm  

Surface  eleva/on    35.7  x  26.8  mm  @20micron  resolu/on  

0   1.3  mm  

Surface  eleva/on  –  Sample  2        53.4  x  25.3  mm  

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Conclussions 1. Cement pore solution is highly alkaline (Na+, K+, and OH- ions)

2. Acid attack reduces the pH of the pore solution

3. Dissolution (leaching) of Portlandite (Ca(OH)2) creates new access routes to existing pores

4. Carbonation-Conversion of Portlandite (33.1 cc/mol) to calcite (36.9 cc/mol) causes blockage of pores

5. Porosity increase/reduction is determined by the competition between leaching/carbonation mechanisms

6. Time is the PRIMARY factor

Hydrated cement-model

Source:httpciks.cbt.nist.gov~garboczappendix1node7.html

http://lmc.epfl.ch/page18839-en.html

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•  The widening of the fracture aperture proves that pre-

existing fractures within cement sheath STILL constitute a primary concern for safe and long-term containment of CO2 in the subsurface.

•  The confining pressure around the cement sheath tends to decrease the aperture. However, even 1µm microfracture can give ~84X10-5 m2 permeability while considering intact cement has a permeability of 10-18-10-20 m2 (Nelson 2006). The human hair diameter approximately 15 to 150 µm!!!

Conclusions

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•  A drilling fluid contaminated composite sandstone-cement core was prepared and cured for 90 days.

•  A CT scan of the sample was obtained prior to plugging it into the Hassler core holder.

•  After 30 hours of injection, the sample taken out of the

core holder because there was loss of pressure. •  The sample retrieved from the core holder was totally de-

bonded.

Latest Experiments….

Cement – formation interface without contamination

Cement – formation interface with contamination

Inadequate mud displacement during cementing leaves residual mud on the formation surface. This residual mud is different from mud cake and is present irrespective of the type of formation being drilled through.

1-300µm

Arrows represent fluid flow.

25mm 25mm

25mm

Schematic of the cement-formation interface

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A2 A1

B1

B2

White arrows show where cross section was taken from A Longitudinal view of Cement – sandstone composite sample B Cross section of Cement – sandstone composite sample

CT Scan of composite sandstone-cement core

Sandstone

Drilling fluid contamination Cement

Cement

Sandstone Drilling fluid contamination

Sandstone

Cement

A1

B1

A2

B2

De-bonded composite sandstone-cement core

Cement with drilling fluid contamination

Sandstone with drilling fluid contamination

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ENGINEERING STRUCTURES-1

39 http://www.google.com/search?hl=en&rlz=1T4ADBF_enUS346US388&prmd=ivns&source=lnms&tbm=isch&ei=z6nuTYGlMcubtwf8_MG2CQ&sa=X&oi=mode_link&ct=mode&cd=2&ved=0CA0Q_AUoAQ&q=oldest%20manmade%20engineering%20structures&biw=1082&bih=580

ENGINEERING STRUCTURES-2

40 http://www.google.com/search?hl=en&rlz=1T4ADBF_enUS346US388&prmd=ivns&source=lnms&tbm=isch&ei=z6nuTYGlMcubtwf8_MG2CQ&sa=X&oi=mode_link&ct=mode&cd=2&ved=0CA0Q_AUoAQ&q=oldest%20manmade%20engineering%20structures&biw=1082&bih=580

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Acknowledgements 41

•  H. Ozyurtkan, Y. ElKhamra, LSU Department of Petroleum Engineering

•  Willson, Clibert, and Best, LSU Civil and Environmental Engineering

•  J.S. Hanor, W. LeBlanc, R. Young, Department of Geology and Geophysics

•  D. Bourgoyne, G. Masterman, J. W. Wooden, LSU Well Facility

•  C. Gardner, L. Dillenbeck, D. Williams, B. Lawrence, Chevron Cementing Team and Chevron ETC Rock/Petrophysics

•  B. Newton,R. Shoultz OMNI Laboratories/ Weatherford

•  D. Beckett, Dylan Jackson, Core Laboratories

•  Argonne National Laboratory, Chicago •  Russ Detwiler, University of California Davies •  George Scherer, Andrew Duguid, Princeton University

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•  HW: •  http://www.ted.com/talks/

richard_sears_planning_for_the_end_of_oil.html

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Questions? And Thank You!

43

44 http://oceanexplorer.noaa.gov/explorations/06mexico/background/oil/media/types_600.html

1, 2) conventional fixed platforms; 3) compliant tower; 4, 5) vertically moored tension leg and mini-tension leg platform; 6) Spar ; 7,8) Semi-submersibles ; 9) Floating production, storage, and offloading facility; 10) sub-sea completion and tie-back to host facility.

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Fluid migration paths through

wellbores

Source: Bourgoyne et al,1999

http://photos.mongabay.com/09/forecast_co2.jpg

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Tea Pot Dome well cement 3a BSE & EDS

Fe

Ca Cl S

Al

Si

Fe

Fe Ca

Ca

Ca

Ca Ca

Cl

Cl

Si

Si

Si

Si

Si

Al

Al

Al

S

S

S

Mg

Mg

Mg

Na

Na

Na Cl

Cl Fe

Ca

S

Si

Al Mg Na

O

O

O

O

O O

Tea Pot Dome well cement 3a BSE micrographs