Electricity: measuring and testing – Of geophysical surface or subsurface in situ – Using electrode arrays – circuits – structure – or supports
Patent
1998-01-14
2000-05-09
Snow, Walter E.
Electricity: measuring and testing
Of geophysical surface or subsurface in situ
Using electrode arrays, circuits, structure, or supports
324366, G01V 318
Patent
active
060608862
ABSTRACT:
An apparatus for determining radial distribution of resistivity of earth formations surrounding a wellbore. The apparatus includes a sonde mandrel having an insulating exterior surface and electrodes disposed on the insulating surface at spaced apart locations. The electrodes are connected to circuits for measuring a focused current resistivity within a predetermined longitudinal span. The electrodes are also connected to circuits for measuring electrical impedance between pairs of electrodes spaced apart at a plurality of different longitudinal spacings. The preferred embodiment includes a voltage measuring circuit interconnected between a pair of electrodes which is positioned between a closest spaced pair of electrodes connected to the impedance measuring circuits, so that a vertical resolution of the impedance measurements can be limited to approximately the axial spacing of the pair of electrodes connected to the voltage measuring circuit. A method according to the invention for determining the distribution of resistivity of earth formations surrounding a wellbore includes the steps of measuring a focused current resistivity of the earth formations to determine a composite resistivity of an uninvaded zone, an invaded zone and a flushed zone. Impedance is measured between pairs of electrodes, each pair having a different longitudinal spacing, and resistivity of the flushed zone and the invaded zone are determined from the measurements of impedance. The resistivity of the uninvaded zone can then be determined from the measurement of focused current resistivity.
REFERENCES:
patent: 4646026 (1987-02-01), Chemali et al.
Fabris Antonio
Itskovich Gregory B.
Mezzatesta Alberto G.
Tabarovsky Leonty A.
Fagin Richard A.
Snow Walter E.
Western Atlas International Inc.
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