Page 248 - Reservoir Geomechanics

229 Determination of S 3 from mini-fracs

2700

2750

2800
Depth (mRKBMD) 2850

2900

2950
0 45 90 135 180 225 270 315 360
Azimuth (degrees from North)

Tensile fractures
Bit trips
Wash and ream

Figure 7.12. Depths at which drilling-induced tensile fractures were observed in one of the Visund
wells studied by Wiprut, Zoback et al.(2000), along with indications of depths where there were
wash-and-ream operations or bit trips that may have caused sudden increases in wellbore pressure.
Reprinted with permission of Elsevier.

when excessive formation failure blocks the annulus around the bottom-hole assembly
during drilling. To assure that this was not the case, Wiprut, Zoback et al. (2000)
carefully noted depths at which such operations occurred (Figure 7.12) and restricted
analysisofthedrilling-inducedtensilefracturestodepthsatwhichsuchactivitiesdidnot
occur.
The results of the S Hmax analysis based on drilling-induced tensile fractures in the
Visund field are shown in Figure 7.13 (after Wiprut, Zoback et al. 2000) which shows