Changes

[[file:borehole-imaging-devices_fig5.png|thumb|{{figure number|5}}Borehole televiewer image showing breakouts (dark patches) at NNW and SSE.]]

[[file:borehole-imaging-devices_fig5.png|thumb|{{figure number|5}}Borehole televiewer image showing breakouts (dark patches) at NNW and SSE.]]

==Electrical borehole scanning: the formation microscanner<xref ref-type="fn" rid="boreholeimagingfn1">¹</xref>==

==Electrical borehole scanning: the formation microscanner==

Electrical borehole scanning is an extension of the dipmeter technique. In this method, a large number of closely spaced electrodes of 0.2-in. diameter are mounted on a conductive pad and pressed against the borehole wall. The amount of current emitted from each electrode is recorded as a function of azimuth and depth (Figure 6). The tool thus produces a microresistivity map. Currently on the market are versions with two and four imaging pads perpendicular to each other. The resulting image stripes are about 2.5 in. wide and are oriented azimuthally by a downhole magnetometer unit. In a 8.5-in. borehole, the four-pad Formation MicroScanner provides a 45% circumferential coverage. Repeat logging passes can often increase this percentage. By convention, darker gray tones are used for lower resistivities.

Electrical borehole scanning is an extension of the dipmeter technique. In this method, a large number of closely spaced electrodes of 0.2-in. diameter are mounted on a conductive pad and pressed against the borehole wall. The amount of current emitted from each electrode is recorded as a function of azimuth and depth (Figure 6). The tool thus produces a microresistivity map. Currently on the market are versions with two and four imaging pads perpendicular to each other. The resulting image stripes are about 2.5 in. wide and are oriented azimuthally by a downhole magnetometer unit. In a 8.5-in. borehole, the four-pad Formation MicroScanner provides a 45% circumferential coverage. Repeat logging passes can often increase this percentage. By convention, darker gray tones are used for lower resistivities.