State of lithospheric stress and borehole stability at Deep Sea Drilling Project site 504B, eastern equatorial Pacific

Journal Article · Sun Jun 10 00:00:00 EDT 1990 · Journal of Geophysical Research; (United States)

DOI:https://doi.org/10.1029/JB095iB06p09293· OSTI ID:5014234

Morin, R H ^[1]; Newmark, R L ^[2]; Barton, C A ^[3]; Anderson, R N ^[4]

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1. Geological Survey, Denver, CO (United States)
2. Lawrence Livermore National Lab., Livermore, CA (United States)
3. Stanford Univ., CA (United States)
4. Columbia Univ., Palisades, NY (United States)

Hole 504B in the eastern equatorial Pacific is the deepest hole to penetrate oceanic basement, extending more than 1,500 m beneath the seafloor. Two borehole televiewer (BHTV) logs have been combined and processed in terms of both acoustic amplitude and travel time in order to evaluate the extent and distribution of rock failure along the borehole wall. A histogram of borehole enlargements versus azimuth depicts a dominant breakout azimuth of N122.5{degree}E which corresponds to the direction of minimum principal stress S{sub h}. Furthermore, the bimodality of this histogram, with a secondary mode orthogonal to S{sub h}, indicates that a significant number of enlargements are coalesced tensile fractures occurring along the orientation of S{sub H}, the maximum principal stress. The appearance of this orthogonal, bimodal distribution suggests that the regional horizontal stress field is highly anisotropic, a condition supported by seismic data. The frequency of borehole enlargements increases with increasing depth and depicts a systematic structural deterioration of the well bore. The tensile fractures along the S{sub H} azimuth contribute to this degradation and appear to be induced by thermal stresses due to the injection of cold water into hot rock. The frequency of these extensional features does not increase with depth. Rather, their appearances can be directly correlated with shipboard efforts at deliberately cooling the well and/or with the sudden resumption of drilling after the hole had been allowed to reequilibrate thermally for several days. These latter borehole enlargements are more pronounced than those commonly associated with hydraulic fracturing. The mechanism for fracture initiation and growth, based upon temperature contrasts between the well bore fluid and the adjacent rock may enhance rock failure.

• OSTI ID: 5014234
• Journal Information: Journal of Geophysical Research; (United States), Vol. 95:B6; ISSN 0148-0227
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
OCEANIC CRUST
STRESS ANALYSIS
PACIFIC OCEAN
ANISOTROPY
BASEMENT ROCK
BOREHOLES
DATA PROCESSING
DEPTH
EQUATOR
FLUID INJECTION
FRACTURE MECHANICS
GEOLOGIC FRACTURES
SEAWATER
SEISMIC SURVEYS
STABILITY
STRESSES
TENSILE PROPERTIES
THERMAL STRESSES
WELL DRILLING
WELL LOGGING
CAVITIES
DIMENSIONS
DRILLING
EARTH CRUST
GEOLOGIC STRUCTURES
GEOPHYSICAL SURVEYS
HYDROGEN COMPOUNDS
MECHANICAL PROPERTIES
MECHANICS
OXYGEN COMPOUNDS
PROCESSING
SEAS
SURFACE WATERS
SURVEYS
WATER
580000* - Geosciences