Page 251 - Reservoir Geomechanics

232 Reservoir geomechanics

Breakout azimuth
0 90 180 270 360
5390
Ultrasonic televiewer data

5394

5395

5396
5395
5397

Depth (meters) 5398

5399

5400
5400

5401

5402

5403

5404 5405
−60 −40 −20 0 20 40 60
o
Temperature gradient ( C/km)

Figure 7.14. Rotation of wellbore breakouts near a fault at 5399 m in the KTB borehole that can be
modeled as the result of a perturbation of the stress field induced by slip on the fault (Barton and
Zoback 1994). This is illustrated on the right (see text).

illustrated in Figure 6.4, the dark bands on opposite sides of the well correspond to
breakouts. Near the fault at 5399 m there is both an absence of breakouts immediately
above the fault and an apparent rotation of breakout rotation immediately above and
below the fault.
Breakout rotations were first noted in a scientific research well drilled near the San
Andreas fault in southern California (Shamir and Zoback 1992). In that study, it was
shown that slip on active faults was the most likely cause of the breakout rotations.