Trivia_borehole Image.docx

Borehole Image The term "borehole imaging" refers to those logging and data-processing methods that are used to produce centimeter-scale images of the borehole wall and the rocks that make it up. The context is, therefore, that of open hole, but some of the tools are closely related to their cased-hole equivalents. Borehole imaging has been one of the most rapidly advancing technologies in wireline well logging. The applications range from detailed reservoir description through reservoir performance to enhanced hydrocarbon recovery. Specific applications are fracture identification, analysis of small-scale sedimentological features, evaluation of net pay in thinly bedded formations, and the identification of breakouts (irregularities in the borehole wall that are aligned with the minimum horizontal stress and appear where stresses around the wellbore exceed the compressive strength of the rock). The subject area can be classified into four parts:

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Optical imaging

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Acoustic imaging

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Electrical imaging

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Methods that draw on both acoustic and electrical imaging techniques using the same logging tool

Optical imaging The principal application of downhole video has been in air-filled holes in which acoustic and contact electrical images cannot be obtained. Most applications described in the literature are directed at fracture identification or casing inspection.

Acoustic imaging The borehole televiewer operates with pulsed acoustic energy so that it can image the borehole wall in the presence of opaque drilling muds. The amplitudes of the reflected pulses form the basis of the acoustic image of the borehole wall that caused by the shape of the borehole wall itself such as: irregularities. Examples of these irregularities are fractures, vugs, and breakouts.

Electrical imaging The tool does not provide an absolute measurement of formation resistivity but rather a record of changes in resistivity. The resolution of electrical microimaging tools is governed by the size of the buttons, usually a fraction of an inch. In theory, any feature that is as large as the buttons will be resolved. If it is smaller, it might still be detected. The tools can be run as dipmeters.

Conjunctive acoustic and electrical imaging

To some extent, the ultrasonic and electrical images are complementary because the ultrasonic measurements are influenced more by rock properties, whereas the electrical measurements respond primarily to fluid properties. These differences can be accommodated through the combined use of electrical and acoustic imaging.

References: http://petrowiki.org/Borehole_imaging http://wiki.aapg.org/Borehole_imaging_devices