Multiscale determination of in situ stress and fracture properties in reservoirs

In this thesis we address the problem of determining in situ stress and fracture properties in reservoirs using borehole logs and surface seismic reflection data. The dissertation covers four subtopics. The first is the determination of horizontal stress magnitudes from measurements in a borehole. Two types of data used are stress-induced rock failures in the borehole, known as "breakouts," and the dispersions of polarized flexural waves which propagate along the borehole. Traditionally these data are analyzed to derive stress orientations but not magnitudes. To determine the magnitude of stresses directly from breakouts, we use an iterative elastic modeling of stresses around the borehole and Mohr-Coulomb failure criterion to match the borehole deformation. As a second method we use dispersion curves of the two polarized flexural waves and their crossover points. These methods are applied to data from a well in northeastern Venezuela. The combination of these two techniques provides a complete profile of stress as a function of depth since the first method is applied at the breakout depths and the second is applied everywhere else in the borehole. Both borehole methods agree in the estimation of stress orientation and magnitude. The maximum horizontal stress is in the NNW-SSE direction, in agreement with a regional stress model calculated from the relative motions of the Caribbean and South America plates. The magnitudes of principal stresses are on average, SHmax 1.1Sv (Sv: vertical stress) and Shmin 0.9Sv (Shmin: minimum horizontal stress). This suggests strike-slip faulting, consistent with earthquake mechanisms in the region. The in situ stresses play an important role on determining the properties of fractured formation. The azimuth of SHmax determines the preferred orientation of open fractures. Surface seismic reflection data provide the means for detecting the fractures.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Earth, Atmospheric, and Planetary Sciences.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2008

Author dc:creator

• Grandi Karam, Samantha, 1973-

Advisor dc:contributor.advisor

• M. Nafi Toksöz and Mark E. Willis.

• Earth, Atmospheric, and Planetary Sciences.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/43150

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/43150