The quantification of sedimentary controls on fracture intensity and fracture occlusion is important to accurately predict well performance in fractured reservoirs. Previous work has led to generalizations about the relationships between fracture intensity and rock attributes, however these conclusions have been based on inadequate methods for characterizing fracture abundance. Typically, fracture intensity has not been normalized with respect to the range of fracture sizes observed.
We have quantitatively studied fracture arrays in the Cupido Formation of the Sierra Madre Oriental, Mexico, using techniques that permit normalization of fracture intensities. Sampling sites in 42 carbonate beds were chosen so that stratigraphic and structural variables could be isolated. Approximately 13000 fractures were measured from 82 fracture sets. The complete data set allows us to independently assess the effects on fracture intensity due to bed thickness, sedimentary facies and diagenetic processes. Field observations demonstrate that equivalent sedimentary facies can have remarkably different fracture intensities. Similarly, preliminary results of comparing fracture size distributions from 9 carbonate mudstone beds in the same structural domain of a fold limb suggest that bed thickness cannot explain the observed variations of fracture intensity. Conversely, microstructural evidence suggests that compositional and textural characteristics at the time of fracturing are significant controls on fracture intensity in these rocks.
2000 AAPG Annual Meeting
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