3.4 Exadaktylos Borehole stability.ppt - Δομή Δια...

Operational Programme “Education and Lifelong Learning”Continuing Education Programme for updating Knowledge of

University Graduates:

“Modern Development in Offshore Structures”

3.4 Stability of deep boreholes

George ExadaktylosProfessor of Rock Mechanics & Mining Engineering, School of Mineral

Resources Engineering, Technical University of CreteEmail: [email protected]

AUTh TUC

Administrator

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Το παρόν υλικό δημιουργήθηκε στα πλαίσια του Προγράμματος Δια Βίου Μάθησης ΑΕΙ για την Επικαιροποίηση Γνώσεων Αποφοίτων ΑΕΙ "Σύγχρονες Εξελίξεις στις Θαλάσσιες Κατασκευές" (Επιχειρησιακό Πρόγραμμα "Εκπαίδευση και Δια Βίου Μάθηση") για αποκλειστική χρήση από τους εκπαιδευόμενους του Προγράμματος. Τυχόν άλλη χρήση του υλικού ή/και αναπαραγωγή αυτού δεν επιτρέπεται, καθόσον αποτελεί πνευματικό δικαίωμα του εκάστοτε διδάσκοντος.

Contents

• Introductory remarks• Observational background• Homogeneous & isotropic rocks• Anisotropic rocks• Jointed rocks• Size effect• Sand production

Stability of deep boreholes

The aim is to predict and prevent any potential hole instability at large depths, that may result in loss of the wellbore or borehole, based on lab experiments, theoretical mechanics and collection and interpretation of logging data directly in the borehole.

Wellbore instabilities cost $6 billion/year.Instabilities of boreholes may be manifested in the following forms:(1)Borehole breakouts.(2)Excessive borehole deformations

(closure, hole ovalization).(3)Activation of nearby faults or pre‐

existing joints due to alteration of in situ stresses induced by borehole drilling.

Introductory remarks (overview)


Introductory remarks (structure of deep underground space)


Hoek and Brown (1980)

H027.0v

(Hoek &1980)

Ko=100/z+0.3

Ko=1500/z+0.5

Introductory remarks (in situ geostatic stresses)


Approximately 19% of the stress orientation indicators in the World Stress Map (WSM) database have been determined from borehole breakouts. http://dc‐app3‐14.gfz‐potsdam.de/pub/stress_data/stress_data_frame.html

Introductory remarks (World stress map (Mediterranean region)


Deep drilling:• Oil, gas, geothermal energy or

scientific purpose‐oriented wells. • Initially circular openings. • These openings are subjected to

varying pressure, temperature and flow conditions and are more or less efficiently supported depending on whether the drilling fluid penetrates the rock in the course of drilling. At a later stage, the borehole is cased with a steel casing, which can be subject of deformations that may cause failure. Rock failure may also cause wellbore failure.

The problem of the borehole in a deep rock layer

Introductory remarks


Due to the action of significant geostatic and tectonic forces that are encountered at great depths, deep boreholes suffer from severe instabilities, breakouts and exfoliations that can become critical for the progress of the drilling process and may interrupt or even stop energy production. Breakouts lead in general to progressive deterioration of the borehole.



During drilling hole is supported by the mud pressure calculated using mechanical models– low mud‐pressure: hole collapse– high mud‐pressure: formation fracturing, low rate of penetration

Introductory remarks (the mud pressure)

HP m


Theoretical approach: The ability to predict fracture and stress orientations is becoming increasingly important in development of production wells.

Experimental approach: Wireline borehole scanner data to identify the borehole breakouts and its orientation to maximum stress zones.

http://csgexploration.com/Structural%20Geology%20and%20Tectonic%20Analysis.html



http://astro.temple.edu/~davatzes/Methods/Methods/Borehole_Analysis.html



failure in geomaterials may take place in localized deformation in shear bands…. (Vardoulakis and Sulem, 2006)

Observational background (crack propagation)


(Reinecker et al., 2003)

dark vertical bands of lower electrical resistivity

http://www-odp.tamu.edu/publications/204_SR/108/108_f3.htm

Observational background


….or as surface exfoliation (slabbing) and flaking at the wall of a borehole



• Failure in geomaterials takes place in localized deformation in shear bands

• Modelling localization of deformation requires material softening

(Vardoulakis & Muehlhaus, 1986).

Observational background (shear and extensional failure)


Surface parallel cracking and shear banding are thus the dominant failure modes at the borehole wall (Vardoulakis et al., 1988).



• Despite the micromechanisms of failure the final form of breakout is “dog eared”.

• The common denominator is the incipient failure in the form of dilatant microcracking in the zones of the highest compressive stress concentration around the borehole.

Haimson (2007)



Scale (or size) effect in Thick-Walled CylinderObservational background


Borehole closure (KTB deep borehole project)



Casing and tubing collapse due to fault movements (shearing of the casing)

9/9/86

10/12/86

9/9/86

20/12/86 6/3/87: Collapse!

Maury (1990)

Observational backgroundStability of deep boreholes

Homogeneous and isotropic rocks: Stresses and failure criterion


Π1Π2 Π = Pole


2sin32

1)(2

1

2cos3

1)(2

11)(

2

1

2cos34

1)(2

11)(

2

1

4

4

2

2

4

4

2

2

4

4

2

2

2

2

r

R

r

R

r

R

r

R

r

R

r

R

r

R

hHr

hHhH

hHhHr

2sin2122

2

2cos1422

12

2

22

2

222

r

R

r

RuG

r

R

r

R

r

RuG

hH

hHhHr

Outer problem

0,,2

2

2

2

rr r

RP

r

RP

0,22

ur

PRuG r

Inner problem

Kirsch’s (1898) solution assuming isotropic linear elasticity


Lame’s (1852) solution

P

r

RP

r

R

r

R

hHhH

Rr

hHhH

2cos)(2)(

2cos3

1)(2

11)(

2

12

2

4

4

2

2

• the highest stress concentration occurs always at the points of the contour corresponding to θ=0, 180, i.e. along the direction of the minimum principal stress.

• Ιncreasing the borehole pressure results in a decrease of the tangential stress at these points.


Modification of Kirsch’s (1898) stress solution for holes with breakouts to study their stability (Exadaktylos et al., 2003). This analytical solution has been derived by Muskhelishvili’s (1963) methods of complex analysis combined with conformal mapping of the dog‐eared hole on a circle (see figure below).



Hydraulic fracturing case

Stability diagram: Uniform all‐around in situ stresses

Guenot (1987)


Hydraulic fracturing

Spiral failure lines

Spiral failure lines (high internal pressure)

Toroidal fractures

Toroidal fractures

Helical fractures appearing as spiral lines on the walls

Maury (1990)


Failure patterns

Stresses and failure initiation (failure pattern dependent on material behavior)

Anisotropic in situ stresses

Q1

Q2

Q1>Q2


Maury (1990)


Anisotropic in situ stresses

Maury (1990)

(a)


Anisotropic in situ stresses (borehole orientation)

Maury (1990)

Anisotropic rocks



Fairhurst (1965)


Transversely isotropic rocks: Polar diagrams of the tangential stress

Fairhurst (1965)

Jointed rocks


Where the Size effect is important?

•Interpretation of the physical experiments on small holes used to assess the stability of regular (large holes).•Perforations.

Size or scale effect



Size effect & stability of perforations

Exadaktylos and Vardoulakis (2001)

Sand production is a common challenge, especially in unconsolidated and weakly consolidated sand (and sandstones) where 70% of world oil production is achieved (Bianco and Halleck, 2001). Two separate processes are involved, namely:• Sand failure (grain detachment from solid skeleton) • Sand transport by the moving fluid

For an overview of the topic see Rahmati el al. (2013).


Sand production

…Add difficult ground conditions….(creep, swelling)…add fluid flow and pore pressures……add heat flow….

Lame (1852). Leçons sur la théorie mathématique de l'élasticité des corps solides, Gauthier‐Villars, Paris.

Kirsch, 1898, Die Theorie der Elastizität und die Bedürfnisse der Festigkeitslehre. Zeitschrift des Vereines deutscher Ingenieure, 42, 797–807.

Muskhelishvili, N.I., 1963. Some basic problems of the mathematical theory of elasticity. P. Noordhoff Ltd, Groningen, The Netherlands (p. 718).

Exadaktylos G.E., Liolios P.A., Stavropoulou M.C. (2003). A semi‐analytical elastic stress‐displacement solution for notched circular openings in rocks. Int. J. Solids Structures, 40, pp. 1165‐1187.

http://www.economist.com/node/15602848Hoek E. and Brown E.T. 1980. Underground Excavations in Rock. London: Institution of

Mining and Metallurgy 527 pages http://csgexploration.com/Structural%20Geology%20and%20Tectonic%20Analysis.htmlhttp://astro.temple.edu/~davatzes/Methods/Methods/Borehole_Analysis.htmlVardoulakis, I., and J. Sulem. Bifurcation Analysis in Geomechanics. CRC Press, 2006.http://dc‐app3‐14.gfz‐potsdam.de/pub/stress_data/stress_data_frame.htmlVardoulakis & H. B. Muehlhaus, Local Rock Surface Instabilities, Int. J. Rock Mech. ,Win, Sci.

& Geomech. Abstr. Vol. 23, No. 5, pp. 379‐383, 1986.J. Reinecker, M. Tingay and B. Müller (2003), Borehole breakout analysis from four‐arm

caliper logs, World Stress Map Project, http://dc‐app3‐14.gfz‐potsdam.de/pub/guidelines/WSM_analysis_guideline_breakout_caliper.pdf.


References

P.J. van den Hoek, Prediction of different types of cavity failure using bifurcation theory, ARMA ‐ The 38th U.S. Symposium on Rock Mechanics (USRMS), 7‐10 July, Washington, D.C.

I. Vardoulakis, J. Sulem, A. Guenot, Borehole Instabilities as Bifurcation Phenomena, Int. J, Rock Mech. Min. Sci. & Geomech. Abstr. Vol. 25, No. 3, pp. 159‐170, 1988.

B. Haimson, Micromechanisms of borehole instability leading to breakouts in rocks, International Journal of Rock Mechanics & Mining Sciences 44 (2007) 157–173.

Nordbotten & Celia (2012), Geological Storage of CO2 Modeling Approaches for Large‐Scale Simulation, A John Wiley & Sons, Inc., Publication.

Maury V. (1990). An overview of tunnel, underground excavation and borehole collapse mechanisms. Chapter 16, ISRM Symposium (Rock at Great Depth), Pau (France), August 1989 (V. Maury & D. Fourmaintraux Ed’s).

Guenot A. (1987). Contraintes et ruptures autour des forages petrolieres. In Proc. 6th ISRM Cong., 1 (Ed. By Herget and Vongspaisal), pp. 109‐118.

Fairhurst C. (1965). Measurement of in‐situ stresses with particular reference to hydraulic fracturing. Felsmechanik und Ingeniergeologie, v. II (3‐4), 129‐147.

Bianco, L.C.B., and Halleck, P.M., May 2001. Mechanisms of arch instability and sand production in two phase saturated poorly consolidated sandstones. SPE 68932, the SPE European Formation Damage conference, Hague, Netherlands.


Hossein Rahmati et al. (2013). Review of Sand Production Prediction Models. Journal of Petroleum Engineering Volume 2013, Article ID 864981, 16 pages http://dx.doi.org/10.1155/2013/864981.

Exadaktylos G.E., Liolios P.A., Stavropoulou M.C. (2003). A semi‐analytical elastic stress‐displacement solution for notched circular openings in rocks. Int. J. Solids Structures, 40, pp. 1165‐1187.

Exadaktylos, G.E. and Vardoulakis, I. (2001). Microstructure in Linear Elasticity and Scale Effects: A Reconsideration of Basic Rock Mechanics and Rock Fracture Mechanics. Tectonophysics, 335, Nos. 1‐2, pp. 81‐110.


3.4 Exadaktylos Borehole stability.ppt - Δομή Δια...

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