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Fault Condition and Stress Regime Diagram

Fracture Orientation Diagram

Wellbore Stability Diagram

Models of Borehole Stability as a Function of the Local Stress Regime and Borehole Deviation

This page shows the relationship between deviated local stress regimes, horizontal borehole orientation and the inclination of natural and hydraulically induced fractures as well as breakouts.

The following diagrams show the origin of fault condition, fracture and breakout propensity directions in normal faulting, strike slip and reverse faulting stress regimes (after R.R. Hillis and A.F. Williams, 1993, Exploration Geophysics, 24).

 The diagram on the left side gives the relation between stress regime and the fault conditions. 

• SV: Vertical stress
• SH: Maximum horizontal stress
• Sh: Minimum horizontal stress

The fracture orientation diagram indicates the drilling direction for best fracture intersection on dependence of the rock stress regime.

The most stable condition exists if the well axis is oriented perpendicular to the plain of the least stress deviator. The wellbore stability diagram shows the most and least stable horizontal drilling directions for the extensional (normal faulting) and compressional (reverse faulting) stress regimes. In strike slip regimes (SH > SV > Sh), as the ratios SH/SV and Sh/SV increases, i.e. as the stress field becomes "more compressional" and "less extensional", wells should be progressively deviated towards SH-direction to achieve a maximum borehole stability. In strike slip regimes optimal oriented horizontal wellbores are subject to zero stress anisotropy.