Method and apparatus for determining horizontal conductivity and vertical conductivity of earth formations

A method for generating a log of the horizontal conductivity and the vertical conductivity of formations surrounding an earth borehole, comprising the steps of:

• a) moving a logging apparatus through the borehole and deriving values representative of attenuation and phase shift of electromagnetic energy that propagated through a formation from said logging apparatus;
• b) deriving a dip angle of the borehole with respect to the formation;
• c) selecting a horizontal conductivity model value and a vertical conductivity model value;
• d) computing an attenuation-dependent conductivity value and a phase-shift-dependent conductivity value as functions of said horizontal and vertical conductivity model values and said dip angle;
• e) computing an error as a function of the derived attenuation and phase values and the computed conductivity values;
• f) modifying said horizontal and vertical conductivity model values;
• g) repeating steps (d) through (f) until a predetermined criterion of said error is met;
• h) recording modified horizontal and vertical conductivity model values as recorded values;
• and
• i) repeating steps (a) through (h) for a number of depth levels in the borehole to obtain a log of recorded horizontal and vertical conductivity values.

Apparatus for generating a log of the horizontal conductivity and the vertical conductivity of earth formations surrounding a borehole, comprising:

• an elongated logging apparatus having a transmitter coil and at least one receiver coil, the axis of each of said coils being coincident with the axis of said logging apparatus, said logging apparatus including means for deriving first and second formation conductivity values from measurements taken with said coils in the borehole;
• means for selecting a horizontal conductivity model value and a vertical conductivity model value;
• means for computing error values from the differences between:
• (i) first and second composite conductivity values computed as a function of said horizontal and vertical conductivity model values, and (ii) said first and second derived formation conductivity values;
• means for modifying said horizontal and vertical conductivity model values;
• means for repeating implementation by said computing means and said modifying means until predetermined criteria of said error values are met;
• ad
• means for recording modified horizontal and vertical conductivity model values, as recorded values, at a number of depth levels in the borehole to obtain a log of recorded horizontal and vertical conductivity values.

A method for generating a log of the horizontal conductivity and the vertical conductivity of earth formations surrounding a borehole, comprising the steps of:

• a) moving an induction logging apparatus through the borehole, and deriving a first conductivity value from an in-phase induction logging measurement in the borehole and a second conductivity value from a phase quadrature induction logging measurement in the borehole;
• b) deriving a dip angle of the borehole with respect to the formation;
• c) selecting a horizontal conductivity model value and a vertical conductivity model value;
• d) computing an in-phase conductivity value and a phase quadrature conductivity value as functions of said horizontal and vertical conductivity model values and said dip angle;
• e) computing an error as a function of the derived first and second conductivity values and the computed conductivity values;
• f) modifying said horizontal and vertical conductivity model values;
• g) repeating steps (d) through (f until a predetermined criterion of said error is met;
• ad
• h) recording modified horizontal and vertical conductivity model values as recorded values;
• and
• i) repeating steps (a) through (h) for a number of depth levels in he borehole to obtain a log of recorded horizontal and vertical conductivity values.

A method for generating a log of the horizontal conductivity and the vertical conductivity of earth formations surrounding a borehole, comprising the steps of:

• a) moving a logging apparatus having axially aligned coils through the borehole, and deriving first and second formation conductivity values from measurements taken in the borehole with the coils of said logging apparatus, said derived first and second conductivity values being obtained from measurements which are affected differently by the vertical and horizontal conductivities of the formations;
• b) deriving an angle related to the dip of said formations;
• c) computing horizontal and vertical conductivity values from said derived first and second conductivity values and said derived angle;
• d) recording said horizontal and vertical conductivity values, and
• e) repeating steps (a) through (d) for a number of depth levels in the borehole to obtain a log of recorded horizontal and vertical conductivity values.

A method for determining the horizontal conductivity and the vertical conductivity of earth formations surrounding a borehole, comprising the steps of:

• a) deriving first and second formation conductivity values from measurements taken in the borehole, said derived first and second conductivity values being obtained from measurements which are affected differently by the vertical and horizontal conductivities of the formations;
• b) deriving an angle related to the dip of said formations;
• c) computing horizontal and vertical conductivity values from said derived first and second conductivity values and said derived angle;
• and
• d) outputting said horizontal and vertical conductivity values.