B3 Gunnar Skúlason Kaldal
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Transcript of B3 Gunnar Skúlason Kaldal
Structural modeling of casings in high temperature
geothermal wells
05/02/2023
#GGW2016
Gunnar Skúlason Kaldal ([email protected])PhD student at University of Iceland / Engineer at ÍSOR – Iceland GeoSurvey
Magnús Þór Jónsson, Halldór Pálsson and Sigrún Nanna KarlsdóttirUniversity of Iceland
Introduction• PhD project at University of Iceland• Structural models of casings for evaluating well integrity and casing
failure modes• Examples FEM analyses and results• Thermal expansion is one of the most severe structural concerns in
high temperature geothermal wells• Cemented steel casings are constrained by the cement and high forces
generate plastic (permanent) deformations as the casings warm up• Failure modes from thermal expansion (and contraction) include:
• Casing collapse (in the form of a bulge/pucker) • Tensile rupture where the casing (pin) is teared out of the coupling (box) by the
threads or the pipe body
#GGW2016
High temperature geothermal wells• Typical casing program includes 3 casings (API grades)
• Conditions sometimes call for more casings• Casings are cemented over their full length• Perforated liner supports the wellbore in the
production section of the well• Expansion spool is used to allow thermal expansion of
the production casing at the wellhead
Fig: Sigrún Nanna Karlsdóttir
#GGW2016
High temperature geothermal wells• The design of high temperature geothermal wells is
based on API materials and methods, and knowledge gained over the past decades in the geothermal industry
• The design procedure for typical high temperature geothermal wells is good and failures are not very common in conventional wells
• There are however several exceptions• Many parameters influence success of wells• “Structural success” is an important one, for usability
and overall reliability and safety
#GGW2016
Design challenges for the future• Most casing failures that occur in wells are directly related to
large temperature changes and high annular pressure
• Typical wellhead temperatures in high temperature geothermal wells is 200-300°C
• In IDDP-1, still the hottest recorded well to date, superheated steam was produced at the wellhead with temperatures of 450°C
• Future aim is to produce from supercritical source where temperatures could reach as high as 550°C – IDDP-2?
• This provides new challenges in casing design as design standards do not account for these high temperatures
#GGW2016
Failure modes• Collapse (bulge/pucker) – pressure difference/thermal expansion• Tensile rupture – thermal expansion (axial)
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HS Orka / ÍSOR
Adopted from a diagram by Rahman & Chilingarian, 1995
FEM Modeling• The nonlinear behavior of materials, displacements
and friction between contacting surfaces are solved with numerical methods.
• The (Nonlinear) Finite Element Method is used.• Thermal and structural models of the cased section of
the well.• The models are used to evaluate the structural
integrity of the casings when subjected to transient thermo-mechanical loads.
• Three models presented:– Cased section of the well (2D axi-symmetric)– Connection in concrete (2D axi-symmetric)– Section of the well (3D collapse analysis)
i.ii.
iii.
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FEM results1. Cooling due to drilling2. Warm-up3. Discharge (12 minutes)4. Discharge (3 months)
1 2
3 4
700
m
100 m
• Production history modeled.• T-P logs and wellhead data are used as load.• Transient thermal analysis is performed and
the results used as load in the structural analysis.
1. Cooling due to drilling.2. Thermal recovery.3. Discharge (12 min).4. Discharge (3 months).
◦C
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• The wellhead rises as the casing suddenly warms up during discharge.
• The production casing expands and slides inside the wellhead (expansion spool). Wellhead displacement.
Temperature distribution after 9 days of discharge.
Stress-strain curves are implemented for steel. Stress reduction at elevated temperatures is accounted for by scaling E, σy and σu (acc. to Snyder). Friction is defined between
casings and concrete.
Karlsdottir, S.N. and Thorbjornsson, I.O.,2009
FEM results #GGW2016
Wellhead displacement survey
Photographic series of the wellhead of HE-46 during discharge.
52 mm40 mm
Merged photographs of the wellhead of RN-32 after 9 days of discharge.
26 mm
#GGW2016
• Wellhead displacement measured during discharge.
Kaldal, G.S., Jonsson, M.T., Palsson, H., Karlsdottir, S.N., 2015. Structural modeling of the casings in high temperature geothermal wells. Geothermics 55, 126 – 137.
Wellhead displacement survey
#GGW2016
• Modeled wellhead displacement compared to data.
Model resultsKaldal, G.S., Jonsson, M.T., Palsson, H., Karlsdottir, S.N., 2015. Structural modeling of the casings in high temperature geothermal wells. Geothermics 55, 126 – 137.
#GGW2016
• Anchoring of couplings in concrete.• Large stresses are produced near couplings.
Concrete failure
Model i. Cased section of the well Model ii. Coupling in concrete
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• Connection displacement in concrete.• Upward displacement of 5 mm.
Damaged concreteConcrete failure
• Case study: structural analysis of IDDP-1.• Operation history modeled.
• Initial conditions.• Warm-up.• Discharge.• Shut-in and quenching.
Kaldal, G.S., Jonsson, M.T., Palsson, H., Karlsdottir, S.N., 2015. Structural modeling of the casings in high temperature geothermal wells. Geothermics 55, 126 – 137.
Discharge history of IDDP-1
FEM results #GGW2016
Ingason et.al, Geothermics 2013:
• Stress and strain analysis. Discharge phase V of IDDP-1
Anchor casingProduction casing
FEM results #GGW2016
• Permanent strain is generated in the casings during the operation history.
Anchor casingProduction casing
Discharges: Cyclic stress-strain and temperature of the production casing at 50 m depth.
FEM results #GGW2016
• Collapse analysis of the production casing.• Some instability needs to be introduced.
Collapse analysis
0 5 10 15 20 25 30 35 40 450
10
20
30
40
50
60
70
80
90
100
D/t ratio
K55
Col
laps
e pr
essu
re [M
Pa]
Yield strength collapsePlastic collapseTransition collapseElastic collapse9 5/8 (47.0 lb/ft)13 3/8 (68.0 lb/ft)
ISO/TR 10400:
Eigenvalue buckling analysis (theoretical collapse strength).
1
5
2
6
3
7
4
8
Casing: OD = 13 3/8 in, t = 12.2 mmAPI collapse resistance: 13.4 MPa
Eigenvalue buckling analysis (theoretical collapse strength). Nonlinear buckling analysis (includes nonlinearities). Effect of initial geometry; mode shape perturbation, effect of
ovality and external geometric defect. Collapse shape with and without external concrete support.
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Nonlinear buckling analysis.Other defects:
Mode shape perturbation Ovality External defect Water pocket in concrete
Casing: OD = 13 3/8 in, t = 12.2 mmAPI collapse resistance: 13.4 MPa
• Limit load for a perfectly round casing: 38.4 MPa• Limit load using mode shape perturbation: 21.6 MPa • API collapse resistance: 13.4 MPa
0 10 20 30 40 50 60 70 800
10
20
30
40
50
60
Load
, ext
erna
l pre
ssur
e [M
Pa]
UX displacement [mm]
Perfectly round casing1st mode shape perturbation (0.0005 scaling)1st mode shape perturbation (0.001 scaling)Collapse resistance, 13.4 MPa (API, ISO/TR)Elastic collapse (Timoshenko 1961)
Mode shape perturbation
Dmax
Dmin
Effect of ovality
0 10 20 30 40 50 60 70 800
10
20
30
40
50
60
Load
, ext
erna
l pre
ssur
e [M
Pa]
UX displacement [mm]
Perfectly roundOvality (0.1%)Ovality (0.5%)Ovality (1.0%)Ovality (2.0%)Ovality (3.0%)Collapse resistanceElastic collapse
Von Mises stress at collapse: 440 MPaCollapse at 300°C and 20 bar (wall pressure)
Water pocket in concrete
Collapse analysis
Nonlinear buckling analysis
0 50 100 150 200 250 3000
10
20
30
40
50
60
Displacement [mm]
Loa
d, e
xter
nal p
ress
ure
[MPa
]
Concrete support (linear MP)Without concrete support (linear MP)Concrete support (non-linear MP)Without concrete support (non-linear MP)Collapse resistance, 13.4 MPa (API, ISO/TR)Elastic collapse (Timoshenko 1961)
Casing: OD = 13 3/8 in, t = 12.2 mmAPI collapse resistance: 13.4 MPa
Effect of external defect and concrete support
Collapse analysis #GGW2016
Summary and conclusions• Analyses of the casings in high temperature geothermal wells were presented.• High temperature and pressure differences generate many challenges in geothermal wells.• Thermal expansion is one of the major cause of casing failures.• Three models were presented here:
• (i) the cased well, (ii) detailed coupling in concrete and (iii) 3D model of a section (collapse analysis).
• The models are used to evaluate the structural integrity of casings.• Can be used to analyze various load scenarios and material selections.• Conclusions…
#GGW2016
Conclusions - Collapse• Caused by excessive net external pressure• Impurities and geometry (ovality, eccentricity, material..)• Cement integrity and casing roundness (and other defects) have great
effect on collapse resistance of casings• Cement is very important for lateral and radial support• Collapse resistance can be increased by selecting proper materials (HC)
under strict quality control (casing roundness important)• Biaxial loads affect collapse resistance HS Orka / ÍSOR
#GGW2016
Dall‘Acqua et.al 2012 Burst and Collapse Responses of Production Casing in Thermal Applications
Wu et.al 2008 Casing Failures in Cyclic Steam Injection Wells
• Collapse strength reduction due to axial tension is incorporated into API standards (compression not)
• Axial compression plus net external pressure probably also leads to reduction in collapse resistance (is not well known or standardized)
Conclusions – Tensile rupture• Caused by excessive axial tensile stress when casings cool down
after production, i.e. due to long period shut-in or killing operations
• The phenomenon is well understood, but limits of cooling rate or limit in temperature variations ∆T remains unresolved
• The failure mode has occurred in several wells in Iceland in connection to fast cooling while pumping cold water into a hot well
• FEM analyses indicate that:• Failures are more likely to form near changes in outer casings, e.g. at
material grade changes (T95-K55) and near casing shoes
• Thermal gradient between casing layers leads to thermal expansion mismatch which generates stress/strain
• Slow temperature changes have less consequences than fast ones
• The thermal load is more severe for the innermost casing which is in direct contact to the geothermal fluid than external casings (provided that cementing in between is good)
HS Orka / ÍSOR
#GGW2016
Adopted from a diagram by Rahman & Chilingarian, 1995
What further information is needed?• Material integrity at high temperatures >350°C
• Strength reduction• Corrosion• Creep and stress relaxation
• Can wells for 300°C+ be designed within the elastic region of materials?
• Is it possible to quench/cool a >550°C hot well without causing casing failures?
• What can we do to mitigate thermal expansion?
A well known problem of thermal expansion (ΔT day/night)
Conclusions – Looking ahead #GGW2016
Acknowledgements• The University of Iceland research fund• The Technology Development Fund at RANNIS –The Icelandic Centre
for Research• Landsvirkjun – Energy Research Fund• GEORG – Geothermal Research Group
• Reykjavik Energy, ON, HS Orka, Landsvirkjun, Iceland Drilling, Iceland GeoSurvey (ÍSOR), Mannvit and the Innovation Center Iceland.
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Thank you
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