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 method of making resistivity measurements of a formation from a wellbore being drilled, the method comprising:
providing a resistivity measuring tool comprising:
a tool body having a sensor configured to measure the angular position of the tool body relative to the wellbore,
a first axial transmitting antenna including a wire winding symmetric about a longitudinal axis of the tool body for generating an axial magnetic moment,
a second axial transmitting antenna including a wire winding symmetric about a longitudinal axis of the tool body for generating an axial magnetic moment, and
transverse antenna disposed including a wire winding for generating a transverse magnetic moment and located longitudinally between the first and second axial transmitting antennas;
simultaneously transmitting electromagnetic energy into the formation from the first and second axial antennas, thereby inducing a voltage signal related to a formation parameter in the wire winding of the transverse antenna;
combining and processing the signals generated due to the first and second axial transmitting antennas to (i) reduce or remove a formation resistivity anisotropy effect and thereby enhance a bed boundary effect, or (ii) reduce or remove the bed boundary effect and thereby enhance the formation resistivity anisotropy effect;
measuring an angular position of the tool body relative to the wellbore with the sensor; and
correlating the formation parameter with the measured angular position of the tool body.
2. The method of claim 1 , further comprising driving currents to the first and second axial antennas for generating axial magnetic moments in opposite directions, thereby inducing a voltage signal in the wire winding of the transverse antenna related to a parameter of an adjacent bed boundary.
3. The method of claim 1 , further comprising driving currents to the first and second axial antennas for generating axial magnetic moments in the same direction, thereby inducing a voltage signal in the wire winding of the transverse antenna related to a parameter of formation resistivity anisotropy.
4. The method of claim 1 , further comprising:
partitioning a circumference of the tool body into M number of sectors;
defining each data point of the resistivity information by a fidelity function g(Φ);
assigning to each data point a weight for each of the M number of sectors, wherein the weight is associated with an integral of the fidelity function g(Φ) over the sector; and
computing an average of the data points weighted by their respective weights for each of the M sectors.
5. The method of claim 1 , further comprising providing multiple transverse antennas disposed proximate to the outer surface of the tool body and azimuthally-spaced around a circumference of the tool body.