Electrical well logging tool, having an expandable sleeve, for determining if clay is present in an earth formation
First Claim
1. Well logging apparatus comprising:
- a well logging tool having a rigid body, said rigid body being enclosed at least in part by an expandable sleeve;
a plurality of electrodes;
means for mounting said plurality of electrodes on said expandable sleeve;
means for expanding said sleeve in such a manner so as to place said plurality of electrodes in close electrical contact with the sidewall surface of the borehole which is being logged;
a control means;
means for establishing a first signal representative of the pressure in said expandable sleeve;
means for transmitting said first signal to said control means, said control means generating a first control signal to activate said means for expanding said sleeve to pump fluid into said expandable sleeve when it is desired to expand said expandable sleeve, said control means generating a second control signal to stop said means for expanding said sleeve when said first signal indicates that the pressure in said expandable sleeve has reached a desired value, said control means generating a third control signal to reverse the pumping action of said means for expanding said sleeve to return said expandable sleeve to a nonexpanded state when it is desired to move said logging tool, and said control means generating a fourth control signal to stop said means for expanding said sleeve when said first signal indicates that said expandable sleeve has returned to a nonexpanded state.
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Abstract
An electrical well logging system is disclosed wherein the well logging tool is enclosed at least in part by an expandable sleeve having a band of electrodes located in the outer surface thereof. The band of electrodes is located in a plane which is perpendicular to the vertical axis of the well logging tool. When the well logging tool is in a desired position in the borehole, the expandable sleeve is expanded to place the electrodes located therein in contact with the adjacent sidewall surface of the borehole. Current is injected into the formation surrounding the borehole and the voltage induced by the current is measured. A phase comparison of the current injected into the formation and the voltage sensed in response to the injected current can be utilized to determine if clay is present in the formation.
52 Citations
17 Claims
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1. Well logging apparatus comprising:
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a well logging tool having a rigid body, said rigid body being enclosed at least in part by an expandable sleeve; a plurality of electrodes; means for mounting said plurality of electrodes on said expandable sleeve; means for expanding said sleeve in such a manner so as to place said plurality of electrodes in close electrical contact with the sidewall surface of the borehole which is being logged; a control means; means for establishing a first signal representative of the pressure in said expandable sleeve; means for transmitting said first signal to said control means, said control means generating a first control signal to activate said means for expanding said sleeve to pump fluid into said expandable sleeve when it is desired to expand said expandable sleeve, said control means generating a second control signal to stop said means for expanding said sleeve when said first signal indicates that the pressure in said expandable sleeve has reached a desired value, said control means generating a third control signal to reverse the pumping action of said means for expanding said sleeve to return said expandable sleeve to a nonexpanded state when it is desired to move said logging tool, and said control means generating a fourth control signal to stop said means for expanding said sleeve when said first signal indicates that said expandable sleeve has returned to a nonexpanded state. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. In a well logging tool having two current electrodes and four voltage electrodes located therein, apparatus comprising:
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means for injecting alternating electrical current through said two current electrodes into the formation surrounding the borehole into which said logging tool is placed; means for sensing the voltage seen by said four voltage electrodes, said voltage being induced in said formation surrounding said borehole by said injected alternating electrical current; phase comparator means; means for supplying said alternating electrical current to one input of said phase comparator means; means for supplying said voltage to a second input of said phase comparator means, said phase comparator means determining the phase shift between said alternating electrical current and said voltage to give an indication of the presence of clay minerals in said formation surrounding said borehole, said two current electrodes and said four voltage electrodes being oriented in a plane which is perpendicular to the vertical axis of said well logging tool to thereby substantially reduce the effect of spontaneous potentials on the determination of said phase shift, said two current electrodes being located on opposite sides of said well logging tool, two of said four voltage electrodes being located on opposite sides of and equally spaced from a first one of said two current electrodes, the remaining two of said four voltage electrodes being located on opposite sides of and equally spaced from the second one of said two current electrodes, said four voltage electrodes providing symmetry and an averaging effect to the measurement of said voltage being induced in said formation. - View Dependent Claims (12)
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13. A method of well logging comprising the steps of:
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lowering a well logging tool into a borehole, said well logging tool having an expandable sleeve associated therewith, said expandable sleeve having a plurality of electrodes mounted thereon; sensing the pressure seen by said expandable sleeve and generating a first signal representative thereof; pumping fluid into said expandable sleeve when it is desired to expand said expandable sleeve; stopping the pumping of fluid into said expandable sleeve when said first signal indicates that the pressure seen by said expandable sleeve is sufficient to insure that said plurality of electrodes are in close electrical contact with the sidewall surface of said borehole; pumping fluid out of said expandable sleeve when it is desired to move said well logging tool; and stopping the pumping of fluid out of said expandable sleeve when said first signal indicates that the pressure seen by said expandable sleeve is sufficient to insure that said expandable sleeve has returned to an at least partially unexpanded state. - View Dependent Claims (14, 15)
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16. A method of well logging comprising the steps of:
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lowering a well logging tool, having two current electrodes and four voltage electrodes located therein, to a desired depth in a borehole; injecting alternating current through said two current electrodes into the formation surrounding the borehole into which said logging tool is placed; sensing the voltage seen by said four voltage electrodes, said voltage being induced in said formation surrounding said borehole by said injected alternating electrical current; and determining the phase shift between said alternating electrical current and said voltage to give an indication of the presence of clay minerals in said formation surrounding said borehole, said two current electrodes and said four voltage electrodes being oriented in a plane which is perpendicular to the vertical axis of said well logging tool to thereby substantially reduce the effect of spontaneous potentials on the determination of said phase shift, said two current electrodes being located on opposite sides of said well logging tool, two of said four voltage electrodes being located on opposite sides of and equally spaced from a first one of said two current electrodes, the remaining two of said four voltage electrodes being located on opposite sides of and equally spaced from the second one of said two current electrodes, said four voltage electrodes providing symmetry and an averaging effect to the measurement of said voltage being induced in said formation. - View Dependent Claims (17)
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Specification