Electricity: measuring and testing – Of geophysical surface or subsurface in situ – Using electrode arrays – circuits – structure – or supports
Patent
1984-03-30
1986-11-25
Eisenzopf, Reinhard J.
Electricity: measuring and testing
Of geophysical surface or subsurface in situ
Using electrode arrays, circuits, structure, or supports
324347, 324356, G01V 300, G01V 308/3/18
Patent
active
046251731
ABSTRACT:
An electrode insulated from and mounted to the outside of a drill collar in a drill string positioned in a borehole is used for measuring formation spontaneous potential. A current measuring device, such as an ammeter, is connected through a varible ammeter resistor and a switch between the electrode and the drill collar. The ammeter measures current flow from the formation along the walls of the borehole to the drill string to determine the spontaneous potential of the formation at various points along the borehole while it is being drilled. The switch in the ammeter circuit is interrupted at a pre-selected rate and the ammeter current signal is connected through a lock-in amplifier to cancel random noise in the signal and produce an accurate measurement of the very small currents flowing between the electrode and the drill collar. The currents are indicative of spontaneous potentials in the formation. The value of the ammeter resistor is varied and the frequency of closure of the switch is swept over a pre-selected range to measure the time constant of the polarization of the formation along the borehole.
REFERENCES:
patent: 2557168 (1951-06-01), Arps et al.
patent: 2650067 (1953-08-01), Martin
patent: 2694179 (1954-11-01), Walstrom
patent: 3134069 (1964-05-01), Clements et al.
Birchak James R.
Meador Richard A.
Wisler Macmillan M.
Eisenzopf Reinhard J.
Mueller Robert W.
NL Industries Inc.
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