Determination of true formation resistivity

A method for reducing a horn effect to more accurately determine a true formation resistivity using an electromagnetic tool, the method comprising:

• lowering the electromagnetic tool into a wellbore, wherein the electromagnetic tool comprises
• a transmitter attached to the electromagnetic tool, wherein the transmitter comprises a transmitter antenna,
• a first receiver attached to the electromagnetic tool, wherein the first receiver comprises a receiver antenna at a first tilt angle with respect to a longitudinal axis the of electromagnetic tool, and wherein the first receiver and the transmitter are axially separated;
• generating a signal with the transmitter;
• measuring voltage values from the first receiver based on a measurement by the first receiver of the signal, wherein measuring voltage values from the first receiver comprises making measurements during a rotation of the electromagnetic tool, the rotation of the electromagnetic tool partitioned into a number of bins, in which completion of the number of bins is one complete rotation of the electromagnetic tool, wherein the number of bins is greater than one;
• determining an average phase resistivity measurement based on the voltage values;
• determining whether the average phase resistivity measurement corresponds to the true formation resistivity;
• based on the average phase resistivity measurement not corresponding to the true formation resistivity, determining a reevaluated average phase resistivity based on virtual voltage values, wherein the virtual voltage values are determined at a second tilt angle based on the voltage values, the number of bins, a first ratio, and a second ratio, wherein the first ratio is based on the first tilt angle, and wherein the second ratio is based on the number of bins and a difference between the first tilt angle and the second tilt angle;
• and
• determining the true formation resistivity based on the reevaluated average phase resistivity.

A method for reducing a horn effect to more accurately determine a true formation resistivity using an electromagnetic tool, the method comprising:

• lowering the electromagnetic tool into a wellbore, wherein the electromagnetic tool comprises
• a transmitter attached to the electromagnetic tool, wherein the transmitter comprises a transmitter antenna,
• a first receiver attached to the electromagnetic tool, wherein the first receiver comprises a receiver antenna at a first tilt angle with respect to a longitudinal axis of the electromagnetic tool, and wherein the first receiver and the transmitter are axially separated;
• generating a signal with the transmitter;
• measuring voltage values from the first receiver based on a measurement by the first receiver of the signal, wherein measuring voltage values comprises making measurements during a rotation of the electromagnetic tool, the rotation of the electromagnetic tool partitioned into a number of bins, in which completion of the number of bins is one complete rotation of the electromagnetic tool, wherein the number of bins is greater than one;
• determining an average phase resistivity measurement based on the voltage values;
• determining whether the average phase resistivity measurement corresponds to the true formation resistivity;
• based on the average phase resistivity measurement not corresponding to the true formation resistivity, physically adjusting at least one of a tilt angle of the transmitter or the first tilt angle;
• measuring new voltage values from the first receiver;
• determining a reevaluated average phase resistivity based on the new voltage values;
• and
• determining the true formation resistivity based on the reevaluated average phase resistivity.

A method for reducing a horn effect to more accurately determine a true formation resistivity of a using an electromagnetic tool, the method comprising:

• lowering the electromagnetic tool into a wellbore, wherein the electromagnetic tool comprises
• a transmitter attached to the electromagnetic tool, wherein the transmitter comprises a transmitter antenna,
• a first receiver attached to the electromagnetic tool, wherein the first receiver comprises a receiver antenna at a first tilt angle with respect to a longitudinal axis of the electromagnetic tool, and wherein the first receiver and the transmitter are axially separated;
• generating a signal with the transmitter;
• measuring voltage values from the first receiver based on a measurement by the first receiver of the signal, wherein measuring voltage values from the first receiver comprises making measurements during a rotation of the electromagnetic tool, the rotation of the electromagnetic tool partitioned into a number of bins, in which completion of the number of bins is one complete rotation of the electromagnetic tool, wherein the number of bins is greater than one;
• determining an average phase resistivity from the voltage values;
• determining whether the electromagnetic tool is near a boundary based on geosignal responses;
• based on the electromagnetic tool being near the boundary, physically adjusting at least one of a tilt angle of the transmitter or the first tilt angle;
• determining new voltage values from the first receiver;
• determining a new average phase resistivity measurement based on the new voltage values;
• and
• determining the true formation resistivity based on the new average phase resistivity measurement.

A method for reducing a horn effect to more accurately determine a true formation resistivity using an electromagnetic tool, the method comprising:

• lowering the electromagnetic tool into a wellbore, wherein the electromagnetic tool comprises
• a transmitter attached to the electromagnetic tool, wherein the transmitter comprises a transmitter antenna,
• a first receiver attached to the electromagnetic tool, wherein the first receiver comprises a receiver antenna at a first tilt angle with respect to a longitudinal axis of the electromagnetic tool, and wherein the first receiver and the transmitter are axially separated;
• generating a signal with the transmitter;
• measuring voltage values from the first receiver based on a measurement by the first receiver of the signal, wherein measuring voltage values comprises making measurements during a rotation of the electromagnetic tool, the rotation of the electromagnetic tool partitioned into a number of bins, in which completion of the number of bins is one complete rotation of the electromagnetic tool, wherein the number of bins is greater than one;
• determining average phase resistivity measurements based on the voltage values, wherein each of the voltage values are based on one of a plurality of antenna pairs, wherein the each of the plurality of antenna pairs comprises the transmitter and one of the first receiver or a second receiver in the electromagnetic tool;
• determining whether the average phase resistivity measurements correspond to the true formation resistivity based on a comparison of the average phase resistivity measurements;
• based on the average phase resistivity measurements not estimating the true formation resistivity, using geosignal responses to indicate whether the electromagnetic tool is near a boundary;
• based on the geosignal responses indicating that the electromagnetic tool is near the boundary, determining virtual voltage values at a second tilt angle using one or more processors based on the voltage values, the number of bins, a first ratio, and a second ratio, wherein the first ratio is based on the first tilt angle and the second tilt angle, and wherein the second ratio is based on the number of bins and a difference between the first tilt angle and the second tilt angle;
• and
• determining an estimate of the true formation resistivity based on the virtual voltage values using the one or more processors.

A non-transitory machine-readable storage medium storing program code to:

• lowering an electromagnetic tool into a wellbore, wherein the electromagnetic tool comprises
• a transmitter attached to the electromagnetic tool, wherein the transmitter comprises a transmitter antenna,
• a first receiver attached to the electromagnetic tool, wherein the first receiver comprises a receiver antenna at a first tilt angle with respect to a longitudinal axis of the electromagnetic tool, and wherein the first receiver and the transmitter are axially separated;
• generate a signal with the transmitter;
• measure voltage values from the first receiver based on a measurement by the first receiver of the signal, wherein measuring voltage values comprises making measurements during a rotation of the electromagnetic tool, the rotation of the electromagnetic tool partitioned into a number of bins, in which completion of the number of bins is one complete rotation of the electromagnetic tool, wherein the number of bins is greater than one;
• determine virtual voltage values at a second tilt angle using one or more processors based on the voltage values, the number of bins, a first ratio, and a second ratio, wherein the first ratio is based on the first tilt angle and the second tilt angle, and wherein the second ratio is based on the number of bins and a difference between the first tilt angle and the second tilt angle;
• and
• determine an estimate of a true formation resistivity based on the virtual voltage values using the one or more processors.

A system to determine a true formation resistivity using an electromagnetic tool, the system comprising:

• the electromagnetic tool, wherein the electromagnetic tool comprises
• a transmitter attached to the electromagnetic tool, wherein the transmitter comprises a transmitter antenna, and
• a first receiver attached to the electromagnetic tool, wherein the first receiver comprises a receiver antenna at a first tilt angle with respect to a longitudinal axis of the electromagnetic tool, and wherein the first receiver and the transmitter are axially separated;
• one or more processors;
• and
• a non-transitory machine-readable storage medium having program code executable by the one or more processors to:
• generate a signal with the transmitter;
• measure voltage values from the first receiver based on a measurement by the first receiver of the signal, wherein measuring voltage values comprises making measurements during a rotation of the electromagnetic tool, the rotation of the electromagnetic tool partitioned into a number of bins, in which completion of the number of bins is one complete rotation of the electromagnetic tool, wherein the number of bins is greater than one;
• determine virtual voltage values at a second tilt angle based on the voltage values, the number of bins, a first ratio, and a second ratio, wherein the first ratio is based on the first tilt angle and the second tilt angle, and wherein the second ratio is based on the number of bins and a difference between the first tilt angle and the second tilt angle;
• and
• determine an estimate of the true formation resistivity based on the virtual voltage values.

A system to determine a true formation resistivity using an electromagnetic tool, the system comprising:

• the electromagnetic tool, wherein the electromagnetic tool comprises
• a transmitter attached to the electromagnetic tool, wherein the transmitter comprises a transmitter antenna, and
• a first receiver attached to the electromagnetic tool, wherein the first receiver comprises a receiver antenna at has a first tilt angle with respect to a longitudinal axis of the electromagnetic tool, and wherein the first receiver and the transmitter are axially separated;
• one or more processors;
• and
• a non-transitory machine-readable storage medium having program code executable by the one or more processors to:
• generate a signal with the transmitter;
• measure voltage values from the first receiver based on a measurement by the first receiver of the signal, wherein measuring voltage values comprises making measurements during a rotation of the electromagnetic tool, the rotation of the electromagnetic tool partitioned into a number of bins, in which completion of the number of bins is one complete rotation of the electromagnetic tool, wherein the number of bins is greater than one;
• determine an average phase resistivity measurement based on the voltage values;
• determine whether the average phase resistivity measurement corresponds to the true formation resistivity;
• and
• based on the average phase resistivity measurement not corresponding to the true formation resistivity, determine a reevaluated average phase resistivity based on virtual voltage values using the one or more processors, wherein the virtual voltage values are determined at a second tilt angle using the one or more processors based on the voltage values, the number of bins, a first ratio, and a second ratio, wherein the first ratio is based on the first tilt angle and the second tilt angle, and wherein the second ratio is based on the number of bins and a difference between the first tilt angle and the second tilt angle;
• and
• determine the true formation resistivity based on the reevaluated average phase resistivity.

A system to determine a true formation resistivity using an electromagnetic tool, the system comprising:

• the electromagnetic tool, wherein the electromagnetic tool comprises
• a transmitter attached to the electromagnetic tool, wherein the transmitter comprises a transmitter antenna, and
• a first receiver attached to the electromagnetic tool, wherein the first receiver comprises a receiver antenna at a first tilt angle with respect to a longitudinal axis of the electromagnetic tool, and wherein the first receiver and the transmitter are axially separated;
• one or more processors;
• and
• a non-transitory machine-readable medium having program code executable by the one or more processors to:
• generate a signal with the transmitter;
• measure voltage values from the first receiver based on a measurement by the first receiver of the signal, wherein measuring voltage values comprises making measurements during a rotation of the electromagnetic tool, the rotation of the electromagnetic tool partitioned into a number of bins, in which completion of the number of bins is one complete rotation of the electromagnetic tool, wherein the number of bins is greater than one;
• determine an average phase resistivity measurement based on the voltage values;
• determine whether the average phase resistivity measurement corresponds to the true formation resistivity;
• based on the average phase resistivity measurement not corresponding to the true formation resistivity, physically adjust at least one of a tilt angle of the transmitter and the first receiver tilt angle;
• measure new voltage values from the first receiver;
• determine a reevaluated average phase resistivity based on the new voltage values;
• and
• determine the true formation resistivity based on the reevaluated average phase resistivity.

A system to determine a true formation resistivity using an electromagnetic tool, the system comprising:

• the electromagnetic tool, wherein the electromagnetic tool comprises
• a transmitter attached to the electromagnetic tool, wherein the transmitter comprises a transmitter antenna, and
• a first receiver attached to the electromagnetic tool, wherein the first receiver comprises a receiver antenna at a first tilt angle with respect to a longitudinal axis of the electromagnetic tool, and wherein the first receiver and the transmitter are axially separated;
• one or more processors;
• and
• a machine-readable medium having program code executable by the one or more processors to:
• generate a signal with the transmitter;
• measure voltage values from the first receiver based on a measurement by the first receiver of the signal, wherein measuring voltage values comprises making measurements during a rotation of the electromagnetic tool, the rotation of the electromagnetic tool partitioned into a number of bins, in which completion of the number of bins is one complete rotation of the electromagnetic tool, wherein the number of bins is greater than one;
• determine an average phase resistivity from the voltage values;
• determine whether the electromagnetic tool is near a boundary based on geosignal responses;
• based on the electromagnetic tool being near the boundary, physically adjust at least one of a tilt angle of the transmitter or the first tilt angle, and
• determine a new average phase resistivity based on new voltage values from the first receiver;
• and
• determine the true formation resistivity based on the new average phase resistivity.

A system to determine a true formation resistivity using an electromagnetic tool, the system comprising:

• the electromagnetic tool, wherein the electromagnetic tool comprises
• a transmitter attached to the electromagnetic tool, wherein the transmitter comprises a transmitter antenna,
• a first receiver attached to the electromagnetic tool, wherein the first receiver comprises a first receiver antenna at a first tilt angle with respect to a longitudinal axis of the electromagnetic tool, and wherein the first receiver and the transmitter are axially separated, and
• a second receiver attached to the electromagnetic tool, wherein the second receiver comprises a second receiver antenna at an alternate tilt angle with respect to the longitudinal axis of the electromagnetic tool, and wherein the second receiver is axially separated from the transmitter;
• one or more processors;
• and
• a non-transitory machine-readable medium having program code executable by the one or more processors to:
• generate a signal using the transmitter;
• measure voltage voltage values from the first receiver based on a measurement by the first receiver of the signal, wherein measuring voltage values comprises making measurements during a rotation of the electromagnetic tool, the rotation of the electromagnetic tool partitioned into a number of bins, in which completion of the number of bins is one complete rotation of the electromagnetic tool, wherein the number of bins is greater than one;
• determine average phase resistivity measurements based on the voltage values, wherein each of the voltage values are based on one of a plurality of antenna pairs, wherein the each of the plurality of antenna pairs comprises the transmitter and one of the first receiver or a second receiver in the electromagnetic tool;
• determine whether the average phase resistivity measurements correspond to the true formation resistivity based on a comparison of the average phase resistivity measurements;
• and
• based on the average phase resistivity measurements not estimating the true formation resistivity, use geosignal responses to indicate whether the electromagnetic tool is near a boundary;
• based on the geosignal responses indicating that the electromagnetic tool is near the boundary, determine virtual voltage values at a second tilt angle using the one or more processors based on the voltage values, the number of bins, a first ratio, and a second ratio, wherein the first ratio is based on the second tilt angle and either the first tilt angle or the alternate tilt angle, and wherein the second ratio is based on the number of bins and a difference between the second tilt angle and either the first tilt angle or the alternate tilt angle;
• and
• determining an estimate of the true formation resistivity based on the virtual voltage values.

A non-transitory machine-readable storage medium comprising program code to:

• lowering an electromagnetic tool into a wellbore, wherein the electromagnetic tool comprises
• a transmitter attached to the electromagnetic tool, wherein the transmitter comprises a transmitter antenna,
• a first receiver attached to the electromagnetic tool, wherein the first receiver comprises a receiver antenna at a first tilt angle with respect to a longitudinal axis of the electromagnetic tool, and wherein the first receiver and the transmitter are axially separated;
• generate a signal with the transmitter;
• measuring voltage values from the first receiver based on a measurement by the first receiver of the signal, wherein measuring voltage values comprises making measurements during a rotation of the electromagnetic tool, the rotation of the electromagnetic tool partitioned into a number of bins, in which completion of the number of bins is one complete rotation of the electromagnetic tool, wherein the number of bins is greater than one;
• determining an average phase resistivity measurement based on from the voltage values;
• determining whether the average phase resistivity measurement corresponds to a true formation resistivity;
• and
• based on the average phase resistivity measurement not corresponding to the true formation resistivity, determine a reevaluated average phase resistivity based on virtual voltage values, wherein the virtual voltage values are determined at a second tilt angle based on the voltage values, the number of bins, a first ratio, and a second ratio, wherein the first ratio is based on the first tilt angle, and wherein the second ratio is based on the number of bins and a difference between the first tilt angle and the second tilt angle;
• and
• determining the true formation resistivity based on the reevaluated average phase resistivity.

A non-transitory machine-readable storage medium storing program code to:

• lowering an electromagnetic tool into a wellbore, wherein the electromagnetic tool comprises,
• a transmitter attached to the electromagnetic tool, wherein the transmitter comprises a transmitter antenna,
• a first receiver attached to the electromagnetic tool, wherein the first receiver comprises a receiver antenna at a first tilt angle with respect to a longitudinal axis of the electromagnetic tool, and wherein the first receiver and the transmitter are axially separated;
• generating a signal with the transmitter;
• measuring voltage values from the first receiver based on a measurement by the first receiver of the signal, wherein measuring voltage values comprises making measurements during a rotation of the electromagnetic tool, the rotation of the electromagnetic tool partitioned into a number of bins, in which completion of the number of bins is one complete rotation of the electromagnetic tool, wherein the number of bins is greater than one;
• determine an average phase resistivity measurement based on the voltage values;
• determine whether the average phase resistivity measurement corresponds to a true formation resistivity;
• based on the average phase resistivity measurement not corresponding to the true formation resistivity, physically adjust least one of a tilt angle of the transmitter or the first tilt angle;
• measuring new voltage values from the first receiver;
• determine a reevaluated average phase resistivity based on the new voltage values;
• and
• determining the true formation resistivity based on the reevaluated average phase resistivity.

A non-transitory machine-readable storage medium storing program code to:

• lower an electromagnetic tool into a wellbore, wherein the electromagnetic tool comprises
• a transmitter attached to the electromagnetic tool, wherein the transmitter comprises a transmitter antenna,
• a first receiver attached to the electromagnetic tool, wherein the first receiver comprises a receiver antenna at a first tilt angle with respect to a longitudinal axis of the electromagnetic tool, and wherein the first receiver and the transmitter are axially separated;
• generate a signal using the transmitter, wherein one or more processors is coupled to the electromagnetic tool;
• measure voltage values from the first receiver based on a measurement by the first receiver of the signal, wherein measuring voltage values comprises making measurements during a rotation of the electromagnetic tool, the rotation of the electromagnetic tool partitioned into a number of bins, in which completion of the number of bins is one complete rotation of the electromagnetic tool, wherein the number of bins is greater than one;
• determine an average phase resistivity from the voltage values;
• determine whether the electromagnetic tool is near a boundary based on geosignal responses;
• based on the electromagnetic tool being near the boundary, physically adjust at least one of a tilt angle of the transmitter or the first tilt angle;
• determine new voltage values from the first receiver;
• determine a new average phase resistivity measurement based on the new voltage values;
• and
• determine an estimate of a true formation resistivity based on the new average phase resistivity measurement.

A non-transitory machine-readable storage medium storing program code to:

• lower an electromagnetic tool into a wellbore, wherein the electromagnetic tool comprises
• a transmitter attached to the electromagnetic tool, wherein the transmitter comprises a transmitter antenna,
• a first receiver attached to the electromagnetic tool, wherein the first receiver comprises a receiver antenna at a first tilt angle with respect to a longitudinal axis of the electromagnetic tool, and wherein the first receiver and the transmitter are axially separated;
• generate a signal with the transmitter;
• measure voltage values from the first receiver based on a measurement by the first receiver of the signal, wherein measuring voltage values comprises making measurements during a rotation of the electromagnetic tool, the rotation of the electromagnetic tool partitioned into a number of bins, in which completion of the number of bins is one complete rotation of the electromagnetic tool, wherein the number of bins is greater than one;
• determine average phase resistivity measurements based on the voltage values, wherein each of the voltage values are based on one of a plurality of antenna pairs, wherein the each of the plurality of antenna pairs comprises the transmitter and one of the first receiver or a second receiver in the electromagnetic tool;
• determine whether the average phase resistivity measurements corresponds to a true formation resistivity based on a comparison of the average phase resistivity measurements;
• based on the average phase resistivity measurements not estimating the true formation resistivity, use geosignal responses to indicate whether the electromagnetic tool is near a boundary;
• based on the geosignal responses indicating that the electromagnetic tool is near the boundary, determine virtual voltage values at a second tilt angle using one or more processors, based on the voltage values, the number of bins, a first ratio, and a second ratio, wherein the first ratio is based on the first tilt angle and the second tilt angle, and wherein the second ratio is based on the number of bins and a difference between the first tilt angle and the second tilt angle;
• and
• determining an estimate of the true formation resistivity based on the virtual voltage values.