Mobil Oil Corporation

D Michael Williams

W D Lyle

A compressional-to-shear wave velocity ratio is measured in a subsurface sandstone formation. Ratios of compressional-to-shear wave velocity are determined over a plurality of shear wave travel times in water-bearing sandstone and shale. The subsurface sandstone formation is identified as being hydrocarbon-bearing when the measured compressional-to-shear wave velocity ratio in the subsurface formation is less than an identified minimum of the compressional-to-shear wave velocity ratios determined for water-bearing sandstone and shale.

Method for identifying hydrocarbon-zones in subsurface formations

A deviated borehole penetrating a subsurface formation and intersected by a formation fracture is surveyed with a borehole televiewer acoustic logging system. Relative fracture dip angle and dip direction calculated from such survey with respect to the borehole axis is transformed into a true fracture dip angle and dip direction with respect to the vertical of the earth's coordinate system.

Acoustic logging method for determining the dip angle and dip direction

A borehole logging tool traverses a subsurface formation known to contain naturally occurring fractures. Acoustic wave energy through the naturally fractured formations is measured by a pair of spaced-apart receivers in the logging tool. The ratio of the tube wave amplitudes measured by the pair of receivers identifies total formation permeability. The differences in the tube wave travel times measured by the pair of receivers identifies matrix permeability. The difference between total formation permeability and matrix permeability is attributable to the naturally occurring fractures in the formation.

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Grapevine, TX, United States of America

D Michael Williams