This reference paper reviews and describes 15 techniques for determining hydraulic fracture azimuth. The techniques described are categorized intocore-based, bore- hole-based, near-wellbore, and regional geologic indicators that can be used to predict or measure hydraulic fracture azimuth. The core based methods include:
circumferential velocity anisotropy,
an elastic strain recovery,
differential strain curve analysis,
axial point load tests,
petrographic examination of micro-cracks,
overcoring of archived core,
drilling-induced fractures in core, and
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.
This paper summarizes the techniques that can be used to determine maximum horizontal stress direction for oil and gas field development. Maximum horizontal stress direction is important for patterning hydraulically-fractured field development wells to optimally drain a reservoir, patterning waterflood wells to optimize recovery, and determining the natural fracture set with the greatest production capacity since the natural fractures that parallel maximum horizontal stress are often the most productive.
The techniques for determining subsurface stress direction described in this report are divided into core-based techniques, borehole-based techniques, near-wellbore techniques, and regional geologic indicators.