Petrophysical properties of the Monterey formation and fracture detection from the sonic log
The Monterey formation is interlayered with rocks of different lithologies and contains high densities of fractures in its more brittle layers. A petrophysical study was made on cores from this formation to find out what factors affect the elastic properties of rocks and the relation between laboratory ultrasonic measurements and the sonic log. The ultrasonic velocities were found to depend strongly on mineralogy, porosity, applied hydrostatic pressure, and wave propagation direction. The elastic property of the rock matrix, as categorized by rock types, can be modeled adequately by the effective medium theory. For practical applications, the velocity-porosity relationship can be described well by straight lines intersecting matrix velocities at zero porosity and the velocity of saturating fluid at about 40% porosity. Modeling of the sonic log using core measurement results shows the applicability of the latter to the sonic log interpretation. The large differences in several depth intervals are due to the prevalence of fractures in these layers and the scale effect, i.e., the incapability of inch-scale cores for sampling large fractures as compared to sonic waves in-situ. The velocity difference is directly related to lithology and layer thickness. This is in agreement with conclusions of other studies on the fracture distribution in the Monterey formation. This leads to the possibility of using the sonic log to detect fracture existence and density in the field once proper models are adopted.
- OSTI ID:
- 542847
- Report Number(s):
- CONF-951013--
- Country of Publication:
- United States
- Language:
- English
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