1
Wellbore Cements Durability Under Geological Sequestration Conditions
MILEVA RADONJIC Tevfik Yalcinkaya,
Nnamdi Agbasimalo, Abiola Olabode, Tao Tao & Dinara Dussenova
LOUISIANA STATE UNIVERSITY
RECS 2011, Birmingham, AL – June 8
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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
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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
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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:
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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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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
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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
14
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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!
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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
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