Spherical focusing method and apparatus for determining the thickness of a zone in an earth formation traversed by a borehole

Claim 1

An apparatus for investigating earth formations traversed by a borehole comprising: (a) means for supporting a plurality of electrodes adapted for movement in the borehole, the electrodes comprising at least one current-emitting electrode adapted for emitting current into the borehole and a plurality of potential measuring electrodes; (b) means for emitting a main current and an auxiliary current from said current-emitting electrode; (c) a first control loop for maintaining a first potential difference between two measure electrodes in one portion of the borehole; (d) a second control loop for maintaining a second potential difference between two measure electrodes in a second portion of the borehole; said first and second control loops arranged to produce auxiliary current flow primarily in the borehole and main current flow primarily in the formation surrounding the borehole; (e) means for measuring the main current; (f) means for measuring the auxiliary current; (g) means for combining the measurements of the main and auxiliary currents to produce a signal representative of the resistivity of a portion of the formation; and (h) means for combining said signals representative of the main and auxiliary currents and the signal representative of the resistivity of the portion of the borehole to produce an output signal representative of the average lateral thickness of a zone in the formation.

Claim 2

An apparatus for investigating earth formations traversed by a borehole comprising: (a) means for supporting a plurality of electrodes adapted for movement in the borehole, the electrodes comprising at least one current-emitting electrode adapted for emitting current into the borehole and a plurality of potential measuring electrodes; (b) means for emitting a main current and an auxiliary current from said current-emitting electrode; (c) a first control loop for maintaining a first potential difference between two measure electrodes in one portion of the borehole; (d) a second control loop for maintaining a second potential difference between two measure electrodes in a second portion of the borehole; said first and second control loops arranged to produce auxiliary current flow primarily in the borehole and main current flow primarily in the formation surrounding the borehole; (e) means for measuring the main current; (f) means for measuring the auxiliary current; (g) means for combining the measurements of the main and auxiliary currents to produce a signal representative of the resistivity of a portion of the formation; and (h) means for combining said signals representative of the main and auxiliary currents and the signal representative of the resistivity of the portion of the borehole to produce an output signal representative of the average lateral thickness of a zone in the formation.

Claim 3

An apparatus for investigating earth formations traversed by a borehole comprising: (a) means for supporting a plurality of electrodes adapted for movement in the borehole, the electrodes comprising at least one current-emitting electrode adapted for emitting current into the borehole, current return electrodes and a plurality of potential measuring electrodes; (b) means for emitting a main current and an auxiliary current from said at least one current-emitting electrode; (c) means for adjusting the potential difference between selected potential measuring electrodes to produce auxiliary current flows primarily in the media adjacent to the electrodes and main current flow primarily in the formation surrounding the electrodes; (d) means for measuring said main and auxiliary currents; (e) means for combining the measurments of the main and auxiliary currents to produce a signal representative of the resistivity of a portion of the formation; and (f) means for combining the measurements of main and auxiliary current with the signal representative of the resistivity to produce an output signal representative of the average lateral thickness of the zone of the formation.

Claim 4

An apparatus for investigating earth formations traversed by a borehole comprising: (a) means for supporting a plurality of electrodes adapted for movement in the borehole, the electrodes comprising at least one current-emitting electrode adapted for emitting current into the borehole, current return electrodes and a plurality of potential measuring electrodes; (b) means for emitting a main current and an auxiliary current from said at least one current-emitting electrode; (c) means for adjusting the potential difference between selected potential measuring electrodes to produce auxiliary current flows primarily in the media adjacent to the electrodes and main current flow primarily in the formation surrounding the electrodes; (d) means for measuring said main and auxiliary currents; (e) means for combining the measurments of the main and auxiliary currents to produce a signal representative of the resistivity of a portion of the formation; and (f) means for combining the measurements of main and auxiliary current with the signal representative of the resistivity to produce an output signal representative of the average lateral thickness of the zone of the formation.

Claim 5

A method for investigating subsurface earth formations traversed by a borehole comprising: (a) moving a plurality of electrodes through the borehole, the electrodes including at least one current-emitting electrode adapted for emitting current into the media surrounding the electrodes and a plurality of potential measuring electrodes; (b) emitting a main current and an auxiliary current from said current-emitting electrode; (c) maintaining a first potential difference between two measure electrodes in one portion of the borehole; (d) maintaining a second potential difference between two measure electrodes in a second portion of the borehole, said first and second potential differences cooperating to produce auxiliary current flow primarily in the borehole and main current flow primarily in the formation surrounding the borehole; (e) measuring the main current; (f) measuring the auxiliary current; (g) combining the measurements of the main and auxiliary currents to produce a signal representative of the resistivity of a portion of the formation; and, (h) combining said signals representative of the main and auxiliary currents and the signal representative of the resistivity of the portion of the borehole to produce an output signal representative of the average lateral thickness of a zone in the formation.

Claim 6

A method for investigating subsurface earth formations traversed by a borehole comprising: (a) moving a plurality of electrodes through the borehole, the electrodes including at least one current-emitting electrode adapted for emitting current into the media surrounding the electrodes and a plurality of potential measuring electrodes; (b) emitting a main current and an auxiliary current from said current-emitting electrode; (c) maintaining a first potential difference between two measure electrodes in one portion of the borehole; (d) maintaining a second potential difference between two measure electrodes in a second portion of the borehole, said first and second potential differences cooperating to produce auxiliary current flow primarily in the borehole and main current flow primarily in the formation surrounding the borehole; (e) measuring the main current; (f) measuring the auxiliary current; (g) combining the measurements of the main and auxiliary currents to produce a signal representative of the resistivity of a portion of the formation; and, (h) combining said signals representative of the main and auxiliary currents and the signal representative of the resistivity of the portion of the borehole to produce an output signal representative of the average lateral thickness of a zone in the formation.

Claim 7

A method for investigating earth formations traversed by a borehole, comprising: (a) moving a plurality of electrodes through the borehole, the electrodes including at least one current-emitting electrode adapted for emitting current into the media surrounding the electrodes and current return electrodes and a plurality of potential measuring electrodes; (b) emitting a main current and auxiliary current from said at least one current-emitting electrode; (c) adjusting the potential difference between selected potential measuring electrodes to produce auxiliary current flow primarily in the borehole surrounding the electrodes and main current flow primarily in the formation surrounding the borehole; (d) measuring said main and auxiliary currents; (e) combining the measurements of the main and auxiliary currents to produce a signal representative of the resistivity of a portion of the formation; and, (f) combining the measurements of the main and auxiliary currents with the signal representative of the resistivity to produce an output signal representative of the average lateral thickness of a zone formation.

Claim 8

A method for investigating earth formations traversed by a borehole, comprising: (a) moving a plurality of electrodes through the borehole, the electrodes including at least one current-emitting electrode adapted for emitting current into the media surrounding the electrodes and current return electrodes and a plurality of potential measuring electrodes; (b) emitting a main current and auxiliary current from said at least one current-emitting electrode; (c) adjusting the potential difference between selected potential measuring electrodes to produce auxiliary current flow primarily in the borehole surrounding the electrodes and main current flow primarily in the formation surrounding the borehole; (d) measuring said main and auxiliary currents; (e) combining the measurements of the main and auxiliary currents to produce a signal representative of the resistivity of a portion of the formation; and, (f) combining the measurements of the main and auxiliary currents with the signal representative of the resistivity to produce an output signal representative of the average lateral thickness of a zone formation.

Claim 9

An apparatus for investigating earth formations traversed by a borehole comprising: (a) means for supporting a plurality of electrodes adapted for movement in the borehole, the electrodes comprising at least one current-emitting electrode adapted for emitting current into the borehole and a plurality of potential measuring electrodes; (b) means for supplying both survey and auxiliary currents to said current-emitting electrode for emission into the media surrounding the supporting means, said survey current returning to a first return electrode for return to the current supplying means and said auxiliary current returning to at least one return electrode located relatively near said current-emitting electrode for return to the current supply means; (c) means for measuring the potential at a plurality of points along said supporting means; (d) means operative in response to the measured potentials for adjusting one of the survey or auxiliary currents to set up a given potential distribution in at least a portion of the borehole whereby the auxiliary current will tend to force the survey current into the formation; (e) means for producing first and second signals functionally related to the main and auxiliary currents; and (f) means for combining said first and second signals to produce an output signal representative of the average lateral thickness of a zone in the formation.

Claim 10

An apparatus for investigating earth formations traversed by a borehole comprising: (a) means for supporting a plurality of electrodes adapted for movement in the borehole, the electrodes comprising at least one current-emitting electrode adapted for emitting current into the borehole and a plurality of potential measuring electrodes; (b) means for supplying both survey and auxiliary currents to said current-emitting electrode for emission into the media surrounding the supporting means, said survey current returning to a first return electrode for return to the current supplying means and said auxiliary current returning to at least one return electrode located relatively near said current-emitting electrode for return to the current supply means; (c) means for measuring the potential at a plurality of points along said supporting means; (d) means operative in response to the measured potentials for adjusting one of the survey or auxiliary currents to set up a given potential distribution in at least a portion of the borehole whereby the auxiliary current will tend to force the survey current into the formation; (e) means for producing first and second signals functionally related to the main and auxiliary currents; and (f) means for combining said first and second signals to produce an output signal representative of the average lateral thickness of a zone in the formation.

Claim 14

A method of measuring a characteristic of earth formations traversed by a borehole comprising: (a) moving a plurality of electrodes through said borehole, the electrodes including at least one current-emitting electrode adapted for emitting current into the media surrounding the electrodes and a plurality of potential measuring electrodes; (b) supplying survey and auxiliary currents to at least one of said electrodes for emission into the media surrounding the electrodes, said survey current returning to a first return electrode for return to the current supply means and said auxiliary current returning to at least one electrode which is relatively near said at least one current-emitting electrode for return to the current supply means; (c) measuring the potential at a plurality of points along said borehole; (d) adjusting one of said survey or auxiliary currents in response to said measured potentials to set up a given potential distribution in at least a portion of the borehole so that the auxiliary current will tend to force the survey current into the formation; (e) producing first and second signals functionally related to said main and auxiliary currents; and (f) combining said first and second signals to produce an output signal representative of the average lateral thickness of a zone in the formation.

Claim 15

A method of measuring a characteristic of earth formations traversed by a borehole comprising: (a) moving a plurality of electrodes through said borehole, the electrodes including at least one current-emitting electrode adapted for emitting current into the media surrounding the electrodes and a plurality of potential measuring electrodes; (b) supplying survey and auxiliary currents to at least one of said electrodes for emission into the media surrounding the electrodes, said survey current returning to a first return electrode for return to the current supply means and said auxiliary current returning to at least one electrode which is relatively near said at least one current-emitting electrode for return to the current supply means; (c) measuring the potential at a plurality of points along said borehole; (d) adjusting one of said survey or auxiliary currents in response to said measured potentials to set up a given potential distribution in at least a portion of the borehole so that the auxiliary current will tend to force the survey current into the formation; (e) producing first and second signals functionally related to said main and auxiliary currents; and (f) combining said first and second signals to produce an output signal representative of the average lateral thickness of a zone in the formation.

Claim 19

An apparatus for investigating earth formations traversed by a borehole comprising: (a) means for supporting a plurality of electrodes adapted for movement in the borehole, the electrodes comprising at least one current-emitting electrode adapted for emitting current into the borehole and a plurality of potential measuring electrodes; (b) means for supplying both survey and auxiliary currents to said current-emitting electrode for emission into the media surrounding the supporting means, said survey current returning to a first return electrode for return to the current supply means and said auxiliary current returning to at least one return electrode located relatively near said current-emitting electrode for return to the current supply means; (c) means for measuring the potential at a plurality of points along said supporting means; (d) means operative in response to the measured potentials for adjusting one of the survey or auxiliary currents to set up a given potential distribution in at least a portion of the borehole whereby the auxiliary current will tend to force the survey current into the formation; (e) means for producing first and second signals functionally related to the main and auxiliary currents; and (f) means for combining said first and second signals to produce an output signal functionally related to the presence of mudcake on the borehole wall.

Claim 20

An apparatus for investigating earth formations traversed by a borehole comprising: (a) means for supporting a plurality of electrodes adapted for movement in the borehole, the electrodes comprising at least one current-emitting electrode adapted for emitting current into the borehole and a plurality of potential measuring electrodes; (b) means for supplying both survey and auxiliary currents to said current-emitting electrode for emission into the media surrounding the supporting means, said survey current returning to a first return electrode for return to the current supply means and said auxiliary current returning to at least one return electrode located relatively near said current-emitting electrode for return to the current supply means; (c) means for measuring the potential at a plurality of points along said supporting means; (d) means operative in response to the measured potentials for adjusting one of the survey or auxiliary currents to set up a given potential distribution in at least a portion of the borehole whereby the auxiliary current will tend to force the survey current into the formation; (e) means for producing first and second signals functionally related to the main and auxiliary currents; and (f) means for combining said first and second signals to produce an output signal functionally related to the presence of mudcake on the borehole wall.

Claim 21

A method of measuring a characteristic of earth formations traversed by a borehole comprising: (a) moving a plurality of electrodes through said borehole, the electrodes including at least one current-emitting electrode adapted for emitting current into the media surrounding the electrodes and a plurality of potential measuring electrodes; (b) supplying survey and auxiliary currents to at least one of said electrodes for emission into the media surrounding the electrodes, said survey current returning to a first return electrode for return to the current supply means and said auxiliary current returning to at least one electrode which is relatively near said at least one current-emitting electrode for return to the current supply means; (c) measuring the potential at a plurality of points along said borehole; (d) adjusting one of said survey or auxiliary currents in response to said measured potentials to set up a given potential distribution in at least a portion of the borehole so that the auxiliary current will tend to force the survey current into the formation; (e) producing first and second signals functionally related to said main and auxiliary currents; and (f) combining said first and second signals to produce an output signal functionally related to the presence of mudcake on the borehole wall.

Claim 22

A method of measuring a characteristic of earth formations traversed by a borehole comprising: (a) moving a plurality of electrodes through said borehole, the electrodes including at least one current-emitting electrode adapted for emitting current into the media surrounding the electrodes and a plurality of potential measuring electrodes; (b) supplying survey and auxiliary currents to at least one of said electrodes for emission into the media surrounding the electrodes, said survey current returning to a first return electrode for return to the current supply means and said auxiliary current returning to at least one electrode which is relatively near said at least one current-emitting electrode for return to the current supply means; (c) measuring the potential at a plurality of points along said borehole; (d) adjusting one of said survey or auxiliary currents in response to said measured potentials to set up a given potential distribution in at least a portion of the borehole so that the auxiliary current will tend to force the survey current into the formation; (e) producing first and second signals functionally related to said main and auxiliary currents; and (f) combining said first and second signals to produce an output signal functionally related to the presence of mudcake on the borehole wall.