Induction method for determining dip angle in subterranean earth formations

A method for determining a dip angle of an earth formation with respect to a borehole in the formation, wherein the method comprises:

• measuring a magnetic coupling between a central set of coils and each of two outer sets of coils in a tool in the borehole, wherein the sets of coils comprise a combination of transmitter and receiver coils,
• wherein the outer sets of coils are symmetrically spaced from the central set of coils;
• and
• obtaining from the measured couplings the dip angle of the formation, wherein the tool includes N outer sets of coils, each set being symmetrically spaced from the central set of coils,
• wherein the dip angle corresponds to:
• α = ∑ 1 N ⁢ ⁢ [ α - n + α + n 2 ] N ,
• wherein α−n is an approximate dip angle obtained from a measured coupling between the central set of coils and one array of the nth outer set of coils, and wherein α+n is an approximate dip angle obtained from a measured coupling between the central set of coils and an opppsing array of the nth outer set of coils.

A method for determining the dip angle of an earth formation with respect to a tool in a borehole in the formation, wherein the method comprises:

• measuring a magnetic coupling between one set of transmitter coils and one or more pairs of symmetrically-spaced receiver coil arrays of a tool in the formation, wherein the pairs of receiver coil arrays are symmetrically spaced about the set of transmitter coils;
• and
• obtaining from the measured coupling the dip angle of the formation, wherein the apparent dip angle α corresponds to α = α - + α + 2 ,
• wherein α− and α+ correspond to the measured values of the formation dip angle based on measurements from receiver coil arrays R− and R+, respectively, and transmitter array T.

A method for determining the dip angle of an earth formation with respect to a tool in a borehole in the formation, wherein the method comprises:

• measuring a magnetic coupling between one set of transmitter coils and one or more pairs of symmetrically-spaced receiver coil arrays of a tool in the formation, wherein the pairs of receiver coil arrays are symmetrically spaced about the set of transmitter coils;
• and
• obtaining from the measured coupling the dip angle of the formation, wherein the tool includes N pairs of symmetrically spaced receiver coil arrays R±n, wherein the dip angle corresponds to:
• α = ∑ 1 N ⁢ ⁢ [ α - n + α + n 2 ] N ,
• wherein α−n is an approximate dip angle obtained from a measured coupling between the transmitter coils and one receiver coil array of the nth pair, and wherein α+n is an approximate dip angle obtained from a measured coupling between the central set of coils and an opposing receiver coil array of the nth pair.