Electricity: measuring and testing – Of geophysical surface or subsurface in situ – Using electrode arrays – circuits – structure – or supports
Patent
1987-08-18
1989-06-06
Eisenzopf, Reinhard J.
Electricity: measuring and testing
Of geophysical surface or subsurface in situ
Using electrode arrays, circuits, structure, or supports
G01V 318
Patent
active
048375187
ABSTRACT:
The resistivity of a geologic formation is measure through drillpipe or casing by applying a low frequency bipolar voltage to the casing and to a ground electrode and traversing the casing with a tool having contractors which are connected to a differential amplifier to detect a differential voltage within the casing caused by current leaving the casing into the formation. The differential amplifier is connected to a unity gain inverter and a switching arrangement for alternately reversing the polarity of the connection of input voltages to the differential amplifier. A switching network alternately connects the outputs of the differential amplifier and the output of the inverter to the input of a low pass filter, and a clock is provided for driving the network in synchronization. The casing and formation resistivities may be measured by applying a voltage along a predetermined length of casing between two contractors which are spaced apart farther and on opposite sides of the differential amplifier pickup contactors. The voltage applied across the formation may be applied to the casing at the earth's surface or downhole adjacent the points of measurement of casing resistivity and formation resistivity.
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Gard Michael F.
Kingman John E. E.
Klein James D.
Atlantic Richfield Company
Edmonds Warren S.
Eisenzopf Reinhard J.
Martin Michael E.
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