In-situ stress variations and hydraulic-fracture containment in layered rock: observations from a mineback experiment
The purpose of this paper is to summarize the results of realistic in-situ experiments which have been conducted in an existing tunnel complex at the US Department of Energy's Nevada Test Site to examine hydraulic fracture propagation in layered rock under many different conditions. These facilities are ideal for hydraulic fracture experiments because they provide a realistic in-situ medium with the appropriate boundary conditions (in-situ stresses, with no face surfaces) yet still allow for detailed examination of the induced fractures and geological features through mineback. Although the experiments are conducted in layered, volcanic-tuffs and not sandstones and shales usually encountered in gas reservoirs, proper application of rock mechanics principles allows the extrapolation of these results to gas reservoir conditions. Small scale hydraulic fraxctures were created at various stratigraphic horizons in inclined, sub-horizontal boreholes drilled from an existing tunnel using dyed-water fracture fluid (0.6 m/sup 3/) injected at low rates (0.05 m/sup 3//minute). The results of these experiments show that determination of the in situ stresses in a reservoir stratigraphic sequence is important for proper design of massive hydraulic fracture treatments, particularly for determining the height of the fracture. This would provide an estimate of whether stress magnitudes in the reservoir rock and bounding layers would result in containment of the fracture or enhance out-of-zone propagation and failure of the treatment. The magnitude of the required compressional stress difference in the bounding layers may depend on a number of factors, including the size of the fracture, fracture pressure, and fluid leakoff. These parameters will be evaluated in larger fracture experiments.
- Research Organization:
- Sandia National Labs., Albuquerque, NM (USA)
- DOE Contract Number:
- AC04-76DP00789
- OSTI ID:
- 6446865
- Report Number(s):
- SAND-82-0282C; CONF-830401-1; ON: DE82010080
- Country of Publication:
- United States
- Language:
- English
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58 GEOSCIENCES
580300 -- Mineralogy
Petrology
& Rock Mechanics-- (-1989)
COMMINUTION
CRACK PROPAGATION
FAILURES
FRACTURES
FRACTURING
GEOLOGY
HYDRAULIC FRACTURES
HYDRAULIC FRACTURING
LAYERS
NATIONAL ORGANIZATIONS
NEVADA TEST SITE
STRATIGRAPHY
STRESSES
TUFF
US DOE
US ORGANIZATIONS