Method for measuring transient electromagnetic components to perform deep geosteering while drilling
First Claim
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1. A method of using an electromagnetic instrument in a borehole in an earth formation comprising:
- (a) changing a current through a transmitter on said instrument and inducing currents in said earth formation, said transmitter having a first axial direction;
(b) receiving first and second transient signals resulting from said induced currents in at least two receivers, a first one of said at least two receivers having an axial direction that is substantially parallel to said first axial direction, and a second one of said at least two receivers having an axial direction inclined to said first axial direction; and
(c) determining from said first and second transient signals a distance to an interface in said earth formationwherein the second transient signal is more sensitive to the distance than is the first transient signal.
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Abstract
A transverse induction transmitter on an instrument induces currents in an earth formation when it is pulsed. Transient measurements made at transverse and axial receivers are used for determination of a distance to a bed boundary. This may be used to control the drilling direction. Alternatively, a transmitter on an instrument having a conductive body induces currents in the earth formation. Transient signals are measured and the effect of the conductive body is removed by using a reference signal measured in a homogenous space.
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Citations
18 Claims
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1. A method of using an electromagnetic instrument in a borehole in an earth formation comprising:
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(a) changing a current through a transmitter on said instrument and inducing currents in said earth formation, said transmitter having a first axial direction; (b) receiving first and second transient signals resulting from said induced currents in at least two receivers, a first one of said at least two receivers having an axial direction that is substantially parallel to said first axial direction, and a second one of said at least two receivers having an axial direction inclined to said first axial direction; and (c) determining from said first and second transient signals a distance to an interface in said earth formation wherein the second transient signal is more sensitive to the distance than is the first transient signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. An apparatus for use in a borehole in an earth formation comprising:
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(a) an instrument including a transmitter which induces currents in said earth formation, said transmitter having a first axial direction; (b) at least two receivers on said instrument which receive first and second transient signals resulting from said induced currents, a first one of said at least two receivers having an axial direction that is substantially parallel to said first axial direction, and a second one of said at least two receivers having an axial direction inclined to said first axial direction; and (c) a processor which determines from said first and second transient signals a distance to an interface in said earth formation wherein the second transient signal is more sensitive to the distance than is the first transient signal. - View Dependent Claims (12, 13, 14, 15, 16, 17, 18)
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Specification