Drilling Risk Reduction

In highly stressed environments, strong Earth shear can be a source of failures at multilateral junctions and along the wellbore. Similar stability problems around sidetracks can be reduced if there is flexibility with the location of the kick-off point acquired from knowing the stress conditions at the time of the sidetrack.


PSI views Geomechanics as comprising two fundamentally different parts, Rock Physics and Earth Stresses. Traditionally these have been seen as one as shown in the diagram below taken from Schlumberger’s 1999 Mechanical Earth Model, both sets of information being totally derived from measured data such as well-logs, minifracs, laboratory rock strength tests, etc.

Extended Reach

Except in some cases of high (reverse fault) stress and soft rock conditions, there is no reason why an ideal drilling direction for a horizontal wellbore cannot be found if the full 3D stress volume is known.

Pressure-Depth Graphs

A stress volume created from the seismic reflection mapping contains the 3D direction and magnitude of each of the three principle, mutually perpendicular stresses SH, Sh and SV. These can be plotted quantitatively with depth and stratigraphy, plus SHD, resulting in a well planning chart for any well displaying the frac gradient (Sh) for low tensile strength rocks, the load (SV) and the compressive stress (SH).

Geological Hazards

Studying a stress section with a planned well trajectory and a pressure-depth graph, the geophysicist can mark potentially active faults which are best traversed perpendicularly by the wellbore. The geologist can relate areas of high stress and fault planes likely to be fractured or prone to sloughing to zones of mud loss. This allows the well planning engineer to redesign the well trajectory in the early stages of planning.

Overpressure - Compression

4DGeoStress can estimate overpressure in areas where the excess pore pressure has deformed relatively impermeable shales to the extent that an over-pressured horizon can be distinguished as a thickened unit within a sequence of otherwise thinning units comprising a growing structure.

Overpressure - Extension

Under Fault seal it was shown that less steeply dipping normal faults can seal and 4DGeoStress can detect increasing seal by analysing the average dip of the fault plane for each isochore. Numerous papers on the Gulf of Mexico show examples of this and also demonstrate that over pressure increases with depth as down to basin faults flatten into shaley sequences.

Pre- versus Post-Drill Stress Costs

Seismically derived full stress data are of minimal cost and ready pre-drill. PSI’s stress from seismic is clearly better, less costly and more timely for development drilling than expensive, time consuming, point source wellbore breakout data.