Relationship between in-situ stress and fractures and faults in the Monterey Formation, Santa Maria Basin, California
- Stanford Univ., CA (United States)
Borehole televiewer (BHTV) data from four wells within the on- and offshore Santa Maria Basin were utilized to investigate the relationship between fracture distribution, orientation, and variation with depth and in situ stress. Analysis of stress-induced wellbore breakouts in each well shows a uniform NE-SW maximum horizontal stress (S[sub Hmax]) orientation with depth. This is consistent with the regional S[sub Hmax] direction throughout the entire seismogenic part of the crust as determined from other wellbore breakout data, NW-SE trends of active fold axes and results of kinematic stress-inversion of earthquake focal plane mechanisms. In marked contrast to the uniform stress field, analysis of fractures indicates that their orientation, dip, and frequency vary considerably within each well and laterally among them. With depth, fractures can be generally divided into distinct subsets on the basis of fracture frequency and predominant strike and dip directions. These subsets correlate with changes of lithology and physical properties indicating that factors such as tectonic history, diagenesis and structural variations may have strongly influenced the initiation and propagation of fractures. Only in the onshore well do steeply-dipping fractures strike parallel to S[sub Hmax] and are interpreted as Mode I extension fractures. In the three offshore wells, the fracture strike is mainly oblique or orthogonal to S[sub Hmax] suggesting that they may be distributed strike-slip or reverse faults. We believe currently active faults in the NE-SW transpressional deformation regime play a crucial role for fluid migration by providing permeability enhanced flow paths. Drill stem tests conducted in two of the offshore wells indicate that formation permeability is greatly enhanced in sections of the well where fractures strike predominantly perpendicular to S[sub Hmax] and dip at moderate to steep angles.
- OSTI ID:
- 6858535
- Report Number(s):
- CONF-960527-; CODEN: AABUD2
- Journal Information:
- AAPG Bulletin, Vol. 5; Conference: Annual convention of the American Association of Petroleum Geologists, Inc. and the Society for Sedimentary Geology: global exploration and geotechnology, San Diego, CA (United States), 19-22 May 1996; ISSN 0149-1423
- Country of Publication:
- United States
- Language:
- English
Similar Records
Observations of wellbore failure in the Toa Baja well - Implications for the state of stress in the North Coast Tertiary Basin, Puerto Rico
Application of borehole images to geologic modeling of an eolian reservoir
Related Subjects
47 OTHER INSTRUMENTATION
BOREHOLES
WELL LOGGING
CALIFORNIA
PETROLEUM DEPOSITS
SEDIMENTARY BASINS
GEOLOGIC FAULTS
CAVITIES
DEVELOPED COUNTRIES
GEOLOGIC DEPOSITS
GEOLOGIC FRACTURES
GEOLOGIC STRUCTURES
MINERAL RESOURCES
NORTH AMERICA
RESOURCES
USA
020200* - Petroleum- Reserves
Geology
& Exploration
440400 - Well Logging Instrumentation