Compressive and tensile failure in verticalwells

Stress around circular cavity

© Cambridge University Press (Fig. 6.1, pp. 169)Zoback, Reservoir Geomechanics

Kirsch solution

Example

© Cambridge University Press (Fig. 6.2a, pp. 171)Zoback, Reservoir Geomechanics

Along azimuth of Along azimuth of

© Cambridge University Press (Fig. 6.2b,c, pp. 171)Zoback, Reservoir Geomechanics

Variation of wellbore stresses

© Cambridge University Press (Fig. 6.3a, pp. 173)Zoback, Reservoir Geomechanics

Wellbore breakout region

© Cambridge University Press (Fig. 6.3b,c, pp. 173)Zoback, Reservoir Geomechanics

Mudweight stabilization

As increases, decreases and increases.

© Cambridge University Press (Fig. 6.3b, pp. 173 and Fig. 6.5a,pp. 177)

Zoback, Reservoir Geomechanics

Breakouts as indicators of far-�eldstressesSimplify Kirsch equations at wellbore wall , so

has min at 0 and 180

has min at 90 and 270 , so

Tensile induced fractures

© Cambridge University Press (Fig. 6.5a, pp. 177)Zoback, Reservoir Geomechanics

Safe drilling mud window

Mud weight too lowBreakouts

Mud weight too highTensile induced fractures leading to lost circulation

Imaging breakouts

Ultrasonic -wave Electrical resistivity Breakout cross-section

© Cambridge University Press (Fig. 6.4a,b,c, pp. 176)Zoback, Reservoir Geomechanics

Four-arm caliper data

Caliper data Breakout indication Examples of variations

© Cambridge University Press (Fig. 6.9a,b,c, pp. 183)Zoback, Reservoir Geomechanics