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Fractures and Stress |
Schlumberger Cambridge Research, Madingley Road, Cambridge CB3 0EL, UK
Schlumberger-Doll Research, Old Quarry Road, Ridgefield, CT 06877, USA
Fractures crossing the borehole are probed using electrical currents generated by Formation MicroScanner* pads and Stoneley waves generated by an acoustic source. New techniques have been developed to invert these measurements for estimates of equivalent fracture aperture, a crucial parameter controlling the fluid flow in fractured reservoirs. The objective of this paper is twofold: first, to compare aperture estimates in a variety of rock types; and second to exploit the different physical measurements in order to improve our understanding of the fracture system. Single fractures in controlled borehole experiments are used to cross-validate the two techniques, and good comparisons were found in the aperature range from 10 µm to several millimetres. Core data, acoustic borehole televiewer images, and in one case results using the Dual Laterolog* measurement serve as supporting evidence. Three case studies are presented: one from crystalline rocks, another from a chalk and shale sequence, and a third one from a fractured dolomite reservoir. In these case studies we found that a combined analysis of the two methods yields valuable additional information concerning fracture extent, fracture connectivity and borehole effects such as fracture enlargement and borehole rugosity.
