| 摘要 |
The present invention is a system and method capable of providing continuous measurements of resistivity-through-casing (RTC) of a geological formation traversed by a boreholeby eliminating measurement of the casing resistance. To this end, a real-time feedback control substantially eliminates current flow along the casing in the vicinity of an injection point for injecting a measuring current into the formation. This allows direct estimation of the measuring current injected into the formation along with the casing voltage used to drive the current into the formation. As a result, there is no need for "nulling" or calibration cycle that requires two step measurements with the RTC tool held stationary. The preferred feedback is by the proportional integral derivative procedure (PID) with a digital signal processor that controls bi-directional steerable current sources supplying one or more current to the casing at various points.
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