Apparatus and methods for making azimuthal resistivity measurements
A resistivity measuring tool used in a drillstring having a drill bit on a distal end for drilling a wellbore in a formation includes a tool body having a longitudinal axis, a sensor configured to measure the angular position of the tool body relative to the wellbore, at least one axial antenna including a wire winding for generating an axial magnetic moment parallel with the longitudinal axis, and at least one transverse antenna. The transverse antenna includes an antenna body disposed within a pocket extending radially inward from an outer surface of the tool body and one or more turns of wire wound around the antenna body, the wire winding generating a transverse magnetic moment orthogonal to the longitudinal axis.
1. A resistivity measuring tool used in a drillstring having a drill bit on a distal end for drilling a wellbore in a formation, the tool comprising:
a tool body having a longitudinal axis;
at least one axial antenna including a wire winding for generating an axial magnetic moment parallel with the longitudinal axis; and
at least one transverse antenna comprising:
an antenna body having a longer axis disposed longitudinally in the tool body; and
a wire coil having a central axis disposed around the antenna body, wherein the wire coil central axis is substantially perpendicular to the longer axis of the antenna body, and wherein the wire coil is configured to generate a transverse magnetic moment orthogonal to the tool body longitudinal axis,
wherein at least one antenna is configured to transmit electromagnetic energy into the formation and induce a voltage signal related to a parameter of the formation in a different antenna.
2. The tool of claim 1 , wherein the at least one transverse antenna is disposed within a pocket extending radially inward from an outer surface of the tool body.
3. The tool of claim 2 , further comprising a non-conducting material disposed within the pocket beneath and around the wire winding.
4. The tool of claim 2 , further comprising a magnetic material disposed within the pocket beneath and around the wire winding.
5. The tool of claim 2 , wherein the pocket extends radially inward from the outer surface a maximum of approximately one inch.
6. The tool of claim 2 , wherein the pocket extends axially a maximum of approximately ten inches.
7. The tool of claim 2 , further comprising an antenna shield having openings therein covering the antenna body and wire winding within the pocket and attached to the tool body.
8. The tool of claim 7 , wherein the openings in the antenna shield are curved.
9. The tool of claim 1 , further comprising multiple transverse antennas proximate to the outer surface of the tool body and azimuthally-spaced around a circumference of the tool body.
10. The tool of claim 9 , wherein the multiple transverse antennas are azimuthally-spaced at or less than 180 degrees apart.
11. The tool of claim 9 , wherein the multiple transverse antennas are connected in series or parallel.
12. The tool of claim 1 , wherein the at least one axial antenna wire winding is symmetric about the longitudinal axis of the tool body.
13. The tool of claim 1 , wherein the at least one axial antenna is a transmitting antenna.
14. The tool of claim 1 , wherein the at least one axial antenna is a receiving antenna.
15. The tool of claim 1 , wherein the at least one transverse antenna is a receiving antenna.
16. The tool of claim 1 , wherein the at least one transverse antenna is a transmitting antenna.
17. The tool of claim 1 , further comprising a sensor configured to measure the angular position of the tool body relative to the wellbore.