Page 218 - Reservoir Geomechanics
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199    Compressive and tensile failures in vertical wells



         a.                                           b.
               0   56   112  168  224  280  336
           3837
                                                                       N




          Depth (meters)                                 W                           E





           3838



                                                                       S
                                                                  BOTTOM
                                                                  OF WELL
                       ANISOTROPIC
                    BREAKOUT FAILURE


            c.                                     d.




                           60 0                                    60 0


                          130 0                                   110 0

                          Bottom                                 Bottom






               Figure 6.16. (a) Ultrasonic televiewer image of breakouts influenced by rock strength anisotropy
               associated with the presence of weak bedding planes cutting across a wellbore at a high angle.
               Note that there are four vertical bands of low reflectivity rather than two as shown in Figure 6.4.
               (b) Cross-sectional view of a breakout influenced by the presence of weak bedding planes shows a
               distinctive four-lobed shape. (c) This can be modeled by slip on bedding planes as the stress
               trajectories bend around the well. (d) When mud weight is increased, the size of the breakouts
               decreases.
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