--> ABSTRACT: Fracture Detection in Low-Permeability Reservoir Sandstone: Comparison of BHTV and FMS Logs to Core, by S. E. Laubach, R. W. Baumgardner, Jr., E. R. Monson, E. Hunt, and K. J. Meador; #91022 (1989)

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Fracture Detection in Low-Permeability Reservoir Sandstone: Comparison of BHTV and FMS Logs to Core

S. E. Laubach, R. W. Baumgardner, Jr., E. R. Monson, E. Hunt, K. J. Meador

Detection and characterization of fractures in low-permeability reservoirs is an important goal of reservoir analysis. Natural fractures may increase porosity in low-permeability rock and may enhance or limit the success of hydraulic fracture treatment. Two logging tools used for fracture detection are the borehole televiewer (BHTV), an acoustic device that maps the smoothness of the borehole wall, and Schlumberger's Formation Microscanner (FMS), a resistivity tool that produces a conductivity map of two 2.8-in. wide strips of the borehole wall. Our analysis compares BHTV and FMS logs to 1,028 ft of core from three wells in the 2,000-ft thick Lower Cretaceous Travis Peak Formation, a sandstone and shale unit that produces gas from low-permeability sandstone in east Texas. Core was obtained from depths of 5,900 to 9,900 ft. The Travis Peak provides a good test of fracture-imaging logs because natural fractures have complex geometry and variable mineral fill and because there are borehole breakouts, drilling-induced fractures, and vertical sedimentary structures that must be distinguished from natural fractures for successful fracture analysis.

Vertical extension fractures in Travis Peak sandstone usually are visible on BHTV and FMS logs, but some fractures were missed by FMS pads. Low-angle natural shear fractures observed in core were not seen on either log. Both BHTV and FMS represent fracture shape and distinguish fractures from borehole breakouts. FMS gives a high-resolution image of fracture shape, but natural fractures could not be distinguished from drilling-induced fractures on either log. Existing commercial BHTV and FMS techniques do not give a quantitative measure of fracture aperture. Fracture orientation is readily obtained for inclined fractures from either BHTV or FMS logs, but the orientation of vertical fractures is commonly ambiguous on both logs. These results show that BHTV and FMS logs are useful adjunc s to core-based fracture studies for evaluation of fractured reservoirs.

AAPG Search and Discovery Article #91022©1989 AAPG Annual Convention, April 23-26, 1989, San Antonio, Texas.