Chapter 11 - CasingCollapseAndShear

8/17/2019 Chapter 11 - CasingCollapseAndShear

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Chapter Eleven:Chapter Eleven: CasingCasingCollapse and Shear Collapse and Shear

Topics Salt Movement

Casing Collapse and Shear

Multi-Lateral Junction Stability


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© 2005 GeoMechanics International2

Chapter Objectives

Be able to describe at least two causes of casing

collapse.

Be able to calculate reservoir pressures thatmay cause casing collapse.


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Mud Weight in Salt SectionsMud Weight in Salt Sections


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Objectives

Model salt creep in openhole using finite element technology

hole closure as a function of time

Simulation using openhole geometry and standard f low laws

for salt

Assumptions

Salt solution due to circulation of mud not considered

Cooling of salt due to circulation of mud roughly estimated

Primary creep of salt not included



Mesh Generation Around Borehole

Finer mesh is used

around the

wellbore than in

the far-field in

order to accurately

measure the

deformation of the

wellbore wall



Deformed Mesh

Green is original mesh

Black is deformed

mesh

The deformation of the

material becomes more

severe at the wellbore

wall and decreases to

very small values a

short distance from the

wellbore



Magnitude of Creep Strain

Hot colors indicate larger values of creep strain.


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Temperature in Germany

Source: Database GGA Hannover,

Schellschmidt 2003

• The salt temperature has a

major influence on salt creep

rates

• Estimation of equilibriumtemperatures from

temperature maps at different

depth levels


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Zechstein Evaporites – 140 deg Celsius

Depth: 4510 m

Stress: 2.29 sg

Flow law: Carter &

HansenYoung's Mod.:

30000 MPa

Pois. ratio: 0.25

Hole size: 12.25“

0

5

10

15

20

25

30

0 1 2 3 4 5 6 7

time (days)

% c l

o s u r e

(

r / / R 0 )

MW = 1.6, Temp = 140

MW = 1.65, Temp = 140

MW = 1.7, Temp = 140

MW = 1.75, Temp = 140

MW = 1.8, Temp = 140

MW = 1.85, Temp = 140

MW = 1.9, Temp = 140

2% closure is

critical forthis operation

Time to reach the critical wellbore hole closure value in the

Zechstein salt for different mud weights


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Hole Closure after 3 Days

Hole closure after 3 days

0

5

10

15

20

25

1.55 1.6 1.65 1.7 1.75 1.8 1.85 1.9 1.95

mud weight [sg]

% c

l o s u r e (

r / / R 0 )

4510 m, 140 °C

4510 m, 151 °C

4670 m, 145° C

4670 m, 156° C

Dependence of

hole closure on

mud weight fordifferent

temperatures

St d S lt D (I)


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Stresses around a Salt Dome (I)

Setup of Finite-Element Model

Light blue – salt; continuous salt layer at bottom;asymmetric salt dome in center

Colors – sediment layers with different densities

2-D cross section


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Stresses around a Salt Dome (II)

The upward movement of the salt causes large stress differences at the top and abovethe salt dome

Typically normal faults are seen in this region

Due to the small stress differences in the salt, one of the principal stresses close to thesurface of the salt dome has to be normal to this surface

This causes significant rotations of the stress tensor


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Stresses around a Salt Dome (III)

The common assumption of the vertical stress being a principal stress is not validanymore

The common assumption that the stress field is approximately constant with magnitudeand orientation over a field is not valid anymore

Stress orientation and stress magnitudes are changing rapidly as a function of position

relative to the salt body


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Problems Related to Salt

Salt creep can cause high loads on casing strings

Creep dependent on

Composition

Temperature Stress

Casing with internal liner is used for cases with high expected casingload

For isotropic loading casing can tolerate higher loads than foranisotropic loading

Anisotropy can be caused by

Oval hole shape

Oval shape of casing

Bad cement

Point loading

Anisotropic stresses

Washouts


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Casing Shear Casing Shear

Casing Deformation under High


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Tectonic Stresses

Highly compressive stress

situations may cause

casing deformation

problems

BP (SPE 74560) reportssuch problems for their

fields in Colombia

Problems Restricted access

Reduced collapse resistance

Wells drilled into faults inactively deforming tectonic

regions have a high likelihood

of shearing as a result of

reactivating the faults


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Sheared Casing – Middle East


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Sheared Casing – Middle East



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Tectonic Stresses

Deformation not related to faults; extends over long hole sections

Early time response with up to 3% deformation within the first 100 days

Casing buckling may be postponed with better casing or a double

casing string, but the most effective way of maintaining casing integrity

is to have a good cement job.


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Example of Casing Shear in Tectonic Area

Problem:

• Production from

100+ wells is lost

instantaneously due

to casing shear.• Recovered pipes

show significant

bend.


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0

100

200

300

400

500

600

700

800

900

1000

1100

1200

0 1 2 3

Pressure, sg

D e p t h

, m e t e r s

Overburden EG353

Least prinicipal

stress

Pore pressure

Hydrostatic pressure

Overburden EG484

Overburden EG161

Overburden EG14

Pore Pressure and Stress vs Depth

The least pr incipal stress value obtained from the step rate test in the southern part

of the field is extremely close or equal to the vertical stress magnitude. In the northern part of the field least principal stress magnitude is significantly

smaller than the vertical stress.

South

North

North

North

The stress in the

area wasconstrained to

determine

whether the

stresses weresufficient to

explain the fault

slip event

Slip event

could have

beenreverse

faulting in

the

shallow

subsurface

Summary of S Analysis (South)


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Summary of SHmax Analysis (South)

Pp

Sv

Shmin

SHmax

Stresses in the

south where the slip

event was observed

displayed Shmin

very close to Sv,

indicating this part of

the field may have

been in a reverse-

faulting stressregime.

Summary of S Analysis (North)


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Summary of SHmax Analysis (North)

Pp

Sv

Shmin

SHmax

Stresses in the

north of the field

were not as highly

compressional,and wells in this

part of the field

have not

experienced

sheared casing.

Modeling Fault-Induced Stress at


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g

the Wellbore Wall

Slip on faults perturbs the stress field and will cause rotations of the stress

Large Scale Breakout Rotation in Well A


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(Larger fault)• The fault size above the well

intersection is 200 meters and thefault intersects well at a depth of 440

meters

• The following can be concluded:

1. Well A is intersected by anactive reverse fault with a dip of

~70 degrees.

2. The stress state needed to

model the rotation is consistent

with the stress derived to thesouth of the field.

3. The fault must have a spatial

extent of at least 1km.

4. The fault is ~10x larger belowthan above the well intersection

This is most likely the fault that caused

the casing shear problems

100

150

200

250

300

350

400

450

500

550

600

6500 90 180 270 360

Azimuth (deg)

NO DATA

NO DATAObserved

Modeled


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Large Scale Breakout Rotation in Well C


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Large Scale Breakout Rotation in Well C

• The observed breakoutrotation in Well C can be

explained by a relatively small

fault (10-100 meters) with a

steep dip, again striking

roughly north-south.

• As on previous slides, the

calculations are consistent

with the determined stress

state (magnitudes and

orientation).

Observed Modeled140

150

160

170

180

190

200

2100 90 180 270 360

Azimuth (deg)

Breakout Rotation Near Fractures in Well D


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Breakout Rotation Near Fractures in Well D

• Small rotations in breakouts also are observed on a very small scale around small

fractures. This implies that even fractures with sizes of ~1 meter are currently active.


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MultiMulti--Lateral Junction StabilityLateral Junction Stability

Stability of Multi Lateral

Max stress


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Junctions

The interference of stresses

between the main bore and a

multilateral can be modeled with

finite element analysis.

Poro elasto-plastic materials

Critical plastic strain as failure

criterion

Arbitrary orientation and

geometry

Level 2 Multilateral


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Level 2 Multilateral

Pore PressureDistribution

around

multilateral isaffected by

production

Vertical scale is

reduces by a

factor of 5(original kick-off

angle is 3°).

Optimum Toolface


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Optimum Toolface

The optimum

direction to kick off

the multilateral can

be modeled based

on the stress fieldand the stress

perturbation

induced by the

main bore.

Maximum Drawdown


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Maximum Drawdown

maximum drawdown

can also be modeled

based on the stress

perturbationsassociated with the

pressure depletion

and the perturbations

around the main bore

and the multilateral.

Cross Sections


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Cross Sections

Stress concentrations between the two wellbores when theyare close enough to interfere with each other.

Further Reading


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Further Reading

Barton, C. A. and M. D. Zoback, 1994. StressPerturbations Associated with Active Faults Penetrated byBoreholes: Evidence for Near Complete Stress Drop and

a New Technique for Stress Magnitude Measurement, J.Geophys. Res. 99(5), 9,373–9,390.

Last, N., Mujica, S., Pattillo, P, Kelso, G., 2002. CasingDeformation in a Tectonic Setting: Evaluation, Impact and

Management. IADC/SPE Drilling Conference in Dallas,Texas, 26-28 February 2002, SPE 74560.

Segall, P., J.R. Grasso, A. Mossop, 1994. PoroelasticStressing and Induced Seismicity near the Lacq Gas

Field, Southwestern France, 99 Jour. Geophys. Res.15,423.

Willson, S.M., Fossum, A.F., Fredrich, J.T., 2003. Assessment of salt loading on well casings. SPE 81820.

Chapter 11 - CasingCollapseAndShear

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