Publication Name: The Sedimentary Basins of WA
Authors: S.D. Mildren, R.R. Hills, T. Fett and P.H. Robinson
Publication Volume: 1
Date Published: July 1994
Number of Pages: 21
Reference Type: Book Section
Abstract:
Borehole breakouts are zones of elliptical wellbore cross-section caused by compressional shear failure ofthe wellbore wall. In vertical wells the long axis of breakout ellipses is parallel to the minimum horizontal contemporary stress direction. Drilling-induced hydraulic fractures are narrow, vertical openings striking
parallel to the maximum horizontal stress and are orthogonal to the long axis of breakout ellipses.
Four-arm caliper data and electrical images from Formation MicroScanner (FMS?) logs run in five wells in the Timor Sea, (Beluga-1, Cleia-1, Harbinger-1, Iris-1 and Shalimar-1), have been analysed for breakouts and drilling-induced hydraulic fractures. Breakouts are predominantly oriented southeast-south-southeast and hydraulic fractures are predominantly oriented northeast. Both modes of wellbore failure can be consistently interpreted in terms of an approximately northeast oriented maximum horizontal stress.
Fault-traps in the Timor Sea are more likely to be sealing if they are oriented southeast. However, more detailed information on stress magnitudes and pore pressures is required to ascertain fault-trap integrity. Data on the contemporary stress field also have implications for the drilling direction of deviated wells, and the orientation of fractures in reservoirs.