Techniques for Determining Subsurface Stress Direction and Assessing Hydraulic Fracture Azimuth

ABSTRACT This reference paper reviews and describes 15 techniques for determining hydraulic fracture azimuth. The techniques described are categorized into core-based, borehole-based, near-wellbore, and regional geologic indicators that can be used to predict or measure hydraulic fracture azimuth. The core based methods include: 1) circumferential velocity anisotropy, 2) anelastic strain recovery, 3) differential strain curve analysis, 4) axial point load tests, 5) petrographic examination of microcracks, 6) overcoring of archived core, 7) drilling-induced fractures in core, and 8) direct observation of over-cored open-hole stress test fractures. The borehole based techniques include: 9) borehole breakouts, 10) borehole deformation, 11) borehole imaging of drilling-induced fractures, and 12) directional gamma ray logging. The near-wellbore techniques provided data on the orientation of the fracture induced during an actual fracture treatment and include: 13) microseismic logging and 14) earth tilt surveys. Finally there are the geologic indicators (Method 15) including earthquake focal mechanisms, fault slip data, surface mapping of neotectonic joints, and volcanic vent alignment. These regional data have been compiled for the World Stress Mapping Project and many maps are available that can be used as a first approximation of stress direction. Experience has shown that the more techniques that can be used in a single well or field, the more reliable the result. The concept or theoretical basis for each technique as well as the benefits and limitations of the techniques are described.