Well logging methods and apparatus for converting spatial derivative measurements to time derivative measurements

Claim 2

Apparatus for converting a spatial derivative well logging measurement to a time derivative measurement comprising: a. a support member adapted for movement through a borehole; b. means carried by said support member and adapted for measuring the spatial derivative of a subsurface characteristic to enable a spatial derivative signal to be produced; c. a cable for supporting said support member in a borehole; d. means responsive to the movement of said cable for generating depth pulses having a time characteristic dependent on the velocity of said cable; and e. converting means responsive to said depth pulses for converting said spatial derivative signal to a time derivative signal.

Claim 3

Apparatus for converting a spatial derivative well logging measurement to a time derivative measurement comprising: a. a support member adapted for movement through a borehole; b. means carried by said support member and adapted for measuring the spatial derivative of a subsurface characteristic to enable a spatial derivative signal to be produced; c. a cable for supporting said support member in a borehole; d. means responsive to the movement of said cable for generating depth pulses having a time characteristic dependent on the velocity of said cable; and e. converting means responsive to said depth pulses for converting said spatial derivative signal to a time derivative signal.

Claim 4

Apparatus for converting a spatial derivative well logging measurement to a time derivative measurement comprising: a. a support member adapted for movement through a borehole; b. means carried by said support member and adapted for measuring the spatial derivative of a subsurface characteristic to enable a spatial derivative signal to be produced; c. a cable for supporting said support member in a borehole; d. means responsive to the movement of said cable for generating depth pulses having a time characteristic dependent on the velocity of said cable; and e. converting means responsive to said depth pulses for converting said spatial derivative signal to a time derivative signal.

Claim 5

The apparatus of claim 1 wherein said converting means includes variable gain means responsive to said depth pulses for varying the effective gain as a function of the rate of said depth pulses, and means for applying said spatial derivative signal to said variable gain means to produce said time derivative signal.

Claim 6

The apparatus of claim 1 wherein said converting means includes first and second impedance means connected in series, means for applying said spatial derivative signal to one side of said series connected impedance means, amplifying means having an input terminal connected to the other side of said series connected impedance means, switch means responsive to said depth pulses for repetitively applying a given potential to the junction point between said series connected impedance means to thereby vary the effective gain of said amplifying means to said spatial gradient signal as a function of said time characteristic of said depth pulses.

Claim 7

Apparatus for investigating the spontaneous potential of earth formations traversed by a borehole, comprising: a. a cable adapted to be lowered in a borehole; b. means supported by said cable for movement through the borehole and adapted for deriving a measure of the potential spatial derivative in the borehole to produce a first measurement; c. means for deriving a measure of the difference between the potentials at a location in the vicinity of said gradient measuring means and a relatively remote point to produce a second measurement; d. means responsive to the movement of said cable for generating depth pulses having a time characteristic dependent on the velocity of said cable; e. converting means responsive to said depth pulses for converting said spatial derivative measurement to a time derivative one; and f. combining means for combining said converted first measurement and second measurement to produce a compensated measure of the spontaneous potential.

Claim 8

Apparatus for investigating the spontaneous potential of earth formations traversed by a borehole, comprising: a. a cable adapted to be lowered in a borehole; b. means supported by said cable for movement through the borehole and adapted for deriving a measure of the potential spatial derivative in the borehole to produce a first measurement; c. means for deriving a measure of the difference between the potentials at a location in the vicinity of said gradient measuring means and a relatively remote point to produce a second measurement; d. means responsive to the movement of said cable for generating depth pulses having a time characteristic dependent on the velocity of said cable; e. converting means responsive to said depth pulses for converting said spatial derivative measurement to a time derivative one; and f. combining means for combining said converted first measurement and second measurement to produce a compensated measure of the spontaneous potential.

Claim 9

In apparatus for investigating a subsurface characteristic by lowering a spatial derivative measuring device on a cable in a borehole in the earth, apparatus for converting the spatial derivative well logging measurement to a time derivative measurement comprising: a. means for producing a signal representative of the spatial derivative of the subsurface characteristic; b. means adapted to be responsive to the movement of a cable for generating depth pulses having a time characteristic dependent on cable velocity; and c. converting means responsive to said depth pulses for converting said spatial derivative signal to a time derivative signal.

Claim 10

In apparatus for investigating a subsurface characteristic by lowering a spatial derivative measuring device on a cable in a borehole in the earth, apparatus for converting the spatial derivative well logging measurement to a time derivative measurement comprising: a. means for producing a signal representative of the spatial derivative of the subsurface characteristic; b. means adapted to be responsive to the movement of a cable for generating depth pulses having a time characteristic dependent on cable velocity; and c. converting means responsive to said depth pulses for converting said spatial derivative signal to a time derivative signal.