ABSTRACT
Over the past few years, the Strain Relaxation (SR) method (or the anelastic strain recovery) has been used for predicting the orientation of induced hydraulic fractures in oil wells. Reliability of the method requires a sensitive measuring device and cores free of natural cracks.
A SR device that uses DC displacement transducers was developed and tested in laboratory and field conditions.
An extended version of the SR method is suggested for laboratory use to predict directions and magnitudes of the in-situ stresses. In the laboratory, effects of pore pressure and natural fractures on SR data are investigated. It is observed that jacketed cores that have been subjected to hydrostatic pressure, expand in all directions on the release of the pressure, and that unjacketed porous cores subjected to the same pressure contracted in all directions during their relaxation period. Agreement between the laboratory azimuth predicted by both type of tests is observed.
The calculated fracture direction suggested by SR data collected through testing cores which contain natural fractures is likely to be perpendicular to the maximum horizontal in-situ stress, thus the calculated direction will be 90° away from the true direction. On-site, the SR method is applied in three different wells. Results from two wells are in a fair agreement with predictions of other fracture orientation detection techniques.
