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STANDARD HANDBOOK OF PETROLEUM & NATURAL GAS ...

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MWD and LWD 977<br />

3. electromagnetic resistivity<br />

4. toroidal system resistivity<br />

Short Normal Resistivity (after Anadrill). The short normal (SN) resistivity sub<br />

provides a real-time measurement of formation resistivity using a 16-in. electrode<br />

device suitable for formations drilled with water-base muds having a moderate<br />

salinity. A total gamma ray measurement is included with the resistivity measurement;<br />

an annular bottomhole mud temperature sensor is optional. The short<br />

normal resistivity sub schematically shown in Figure 4-273 must be attached to the<br />

MWD telemetry tools and operates in the same conditions as the other sensors.<br />

Due to the small invasion and the large diameter of the sonde body, a resistivity<br />

near the true resistivity of the formation is generally measured. This is particularly<br />

true in shale where no invasion takes place. The main applications are:<br />

real-time correlation and hydrocarbon identification<br />

lithology identification for casing point and kick-off point selection<br />

real-time pore pressure analysis based on resistivity trend in shales<br />

resistivity range: 0.2 to 100 R*m<br />

Cover plate<br />

A electrode<br />

M electrode<br />

Figure 4-273. Short normal resistivity sub. (Courtesy Anadrill [113].)

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