Measurement of in situ stresses using hydraulic breakdown pressures
The widely accepted method of in situ stress measurements derived from hydraulic fracture experiments requires careful review. It commonly assumes that tension fractures will form when pore fluid pressure exceeds the tensile strength at the borehole wall. If so, the critical breakdown pressure should increase with an increasing tectonic stress. New experimental evidence from the hydraulic fracturing of sandstone, oil shale, and low-permeability granite which shows that either tension or shear fractures may develop in laboratory samples depending on permeability, pore fluid viscosity, injection rate, and differential stress. All of our samples, including very low permeability granite, failed in shear rather than tension at low injection rates. This is because in higher permeability samples or at slower injection rates, pore fluid diffusion into the samples decreases the effective confining pressure until failure occurs by shear fracture. In this case the critical breakdown pressure decreases with an increase in the differential stress, in direct opposition to the relation for tension fractures. Hydraulic fracturing in regions of significant tectonic stress may well produce shear rather than tension fractures, in which case stress determinations based on presumed tension fractures would lead to erroneous results.
- Research Organization:
- Geological Survey, Menlo Park, CA
- OSTI ID:
- 5262298
- Journal Information:
- EOS, Trans., Am. Geophys. Union; (United States), Journal Name: EOS, Trans., Am. Geophys. Union; (United States) Vol. 57:12; ISSN EOSTA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
040300 -- Oil Shales & Tar Sands-- Drilling
Fracturing & Mining
58 GEOSCIENCES
580300* -- Mineralogy
Petrology
& Rock Mechanics-- (-1989)
BITUMINOUS MATERIALS
CARBONACEOUS MATERIALS
ENERGY SOURCES
FOSSIL FUELS
FRACTURING
FUELS
GRANITES
HYDRAULIC FRACTURING
IGNEOUS ROCKS
OIL SHALES
PERMEABILITY
ROCKS
SANDSTONES
SEDIMENTARY ROCKS
SHEAR
STRESSES
TECTONICS