Knowledge of the direction of hydraulic fractures can impact reservoir management of hydraulically fractured reservoirs. Fracture direction can affect where wells are placed, how well patterns for EOR floods are designed, how fracture treatments are designed, and the stability and fracturing of horizontal wells. This paper presents a field study of six different techniques for determining or predicting the azimuthal orienta- tion of hydraulically induced fractures. The techniques were tested in four wells in northwest New Mexico. The six techniques were compared to one another on the basis of reliability of results, operational requirements, and cost effectiveness.
The techniques tested include:
1) shear acoustic anisotropy measurements on oriented core,
2) anelastic strain recovery measurements on oriented, core,
3) overcoring of fractures induced by microfrac tests,
4) natural and coring induced fractures in oriented core,
5) borehole monitoring of fracture related microseismic events, and
6) borehole televiewer measurements of induced and natural fractures.
All six techniques gave similar results with the average of all the data from all four wells suggesting a hydraulic fracture direction of 41 ø azimuth. This agrees with regional in-situ stress direction for the area (see Zoback and Zoback, 1980). There were only small variations between wells and the fracture direction was consistent with depth over the 300 feet of formation tested. The direction of natural fractures as seen in the core and in the borehole televiewer was similar to the hydraulic fracture direction.
Based on the quality of the measurements and the degree of scatter in the results, the shear acoustic anisotropy and borehole micro-seismic methods appear the most reliable of the different methods. The shear acoustic anisotropy and core fracture techniques were the most cost effective. Anelasfic strain recovery, shear acoustic anisotropy, and drilling induced core fracture methods also have the advantage that they are predictive techniques. Since they measure the direction of maximum horizontal in-situ stress in order to deter- mine fracture direction, they can predict fracture direction before the well is fractured.
Overall, the study shows that fracture direction can be reliably determined with current technology. We would recommend that fracture direction in any given field is best determined by using at least two different methods in at least two wells. We believe fracture direction can profoundly affect the recovery of hydrocarbons from fractured fields and should be a datum that is collected routinely in the development of such fields.