Effect of principal stress magnitudes on hydrofracturing orientation. Final report
Technical Report
·
OSTI ID:6449299
The purpose of this work was to establish the effect of the vertical stress on the direction and inclination of hydrofractures in the vicinity of the borehole wall for a set condition of horizontal stresses, and determine the minimum difference between the two principal horizontal stresses for which hydrofractures cease to be randomly oriented and become aligned with the maximum horizontal stress direction. The study was carried out in the laboratory by use of prismatic specimens of size 5 in. x 5 in. x 7 in. high. Three independent and mutually perpendicular loads were applied to the faces of the specimens to simulate the three principal in situ stresses. Hydrofractures were induced by hydraulically pressurizing a vertical borehole in the center of the specimen. The two tests conducted in Dresser basalt served to verify the results previously obtained in Montello granite. It was found that in massive igneous rocks hydrofractures are vertical and oriented perpendicular to the least horizontal compressive stress (sigma/sub Hmin/) if sigma/sub V/ much greater than or equal to sigma/sub Hmin/ and if sigma/sub Hmax/--sigma/sub Hmin/ much greater than or equal to 200 psi. For a horizontal stress differential less than 200 psi the direction of the resulting vertical hydrofracture is not predictable, but it tends to be only within 25/sup 0/ from perfect perpendicularity to sigma/sub Hmin/. When the vertical stress is smaller than sigma/sub Hmin/, in the great majority of cases hydrofractures initiated in the vertical plane perpendicular to sigma/sub Hmin/ but extended along a horizontal plane so as to be perpendicular to the least principal stress. 1 figure, 2 tables. (RWR)
- Research Organization:
- Wisconsin Univ., Madison (USA). Dept. of Metallurgical and Mineral Engineering
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 6449299
- Report Number(s):
- UCRL-13951
- Country of Publication:
- United States
- Language:
- English
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