Azimuth determination while rotating
Systems and methods for determining azimuth of a wellbore while drilling. A method of drilling a wellbore that includes rotating a drill bit to extend the wellbore into a subterranean formation. The method may further include measuring magnetic toolface with a first magnetometer while rotating the drill bit. The method may further include obtaining a cross-axial magnetic field measurement. The method may further include determining azimuth at a point in the wellbore using at least the magnetic toolface and the cross-axial magnetic field measurement. The method may further include using the azimuth as feedback in the drilling the wellbore.
1. A method of drilling a wellbore, comprising:
rotating a drill bit to extend the wellbore into a subterranean formation;
measuring magnetic toolface with a first magnetometer while rotating the drill bit;
obtaining a cross-axial magnetic field measurement;
determining azimuth at a point in the wellbore using at least the magnetic toolface and the cross-axial magnetic field measurement; and
using the azimuth as feedback in the drilling the wellbore,
wherein the determining the azimuth at the point in the wellbore comprises obtaining gravity vectors, calculating an x component of a magnetic field based on the magnetic toolface and the cross-axial magnetic field measurement, calculating a y component of the magnetic field based on the magnetic toolface and the cross-axial magnetic field measurement, calculating a z component of the magnetic field based on Earth's total magnetic field, the cross-axial magnetic field measurement, and Earth's local magnetic dip angle, and then calculating azimuth using the gravity vectors, the x component of the magnetic field, the y component of the magnetic field, and the z component of the magnetic.
2. The method of claim 1 , wherein the obtaining the cross-axial magnetic field measurement comprises measuring cross-axial magnetic field with a second magnetometer while rotating the drill bit.
3. The method of claim 1 , wherein the obtaining the cross-axial magnetic field measurement comprises determining a calibrated cross-axial magnetic field measurement using a measurement of a cross-axial magnetic field while static from a second magnetometer and magnitude of x- and y-components of a magnetic field as measured by the first magnetometer and the second magnetometer while static.
4. The method of claim 1 , wherein the point is at the first magnetometer.
5. The method of claim 1 , further comprising obtaining measurements of gravity vectors with an accelerometer.
6. A method of drilling a wellbore, comprising:
rotating a drill bit to extend the wellbore into a subterranean formation;
measuring magnetic toolface with a first magnetometer while rotating the drill bit;
obtaining a cross-axial magnetic field measurement;
determining azimuth at a point in the wellbore using at least the magnetic toolface and the cross-axial magnetic field measurement; and
using the azimuth as feedback in the drilling the wellbore,
wherein the determining the azimuth at the point in the wellbore uses the following equation:
A
=
tan
-
1
(
(
G
x
*
B
y
-
G
y
*
B
x
)
*
G
t
B
z
*
(
G
x
2
+
G
y
2
)
-
G
z
*
(
G
x
*
B
x
+
G
y
*
B
y
)
)
wherein A is azimuth, Bx, By, and Bz are each magnetic field vectors, and Gx, Gy, and Gz are gravity vectors measured by an accelerometer, wherein Bx is the cross-axial magnetic field measurement times cosine of the magnetic toolface, wherein By is the cross-axial magnetic field measurement times the cosine of the magnetic toolface, wherein Bz is based on Earth's total magnetic field, the cross-axial magnetic field measurement, and Earth's local magnetic dip angle.
7. The method of claim 1 , wherein the cross-axial magnetic field measurement is obtained with a second magnetometer on a survey tool.
8. The method of claim 1 , wherein the determining the azimuth is performed downhole, at surface of the wellbore, or a combination thereof.
9. A method of drilling a wellbore, comprising:
rotating a drill bit to extend the wellbore into a subterranean formation;
measuring magnetic toolface with a first magnetometer while rotating the drill bit;
obtaining a cross-axial magnetic field measurement with a second magnetometer;
measuring gravity with an accelerometer to obtain gravity vectors;
determining azimuth at a point in the wellbore using at least the magnetic toolface and the cross-axial magnetic field measurement, wherein determining the azimuth at the point in the wellbore uses the following equation:
A
=
tan
-
1
(
(
G
x
*
B
y
-
G
y
*
B
x
)
*
G
t
B
z
*
(
G
x
2
+
G
y
2
)
-
G
z
*
(
G
x
*
B
x
+
G
y
*
B
y
)
)
wherein A is azimuth, Bx, By, and Bz are each magnetic field vectors, and Gx, Gy, and Gz are the gravity vectors measured, wherein Bx is the cross-axial magnetic field measurement times cosine of the magnetic toolface, wherein By is the cross-axial magnetic field measurement times the cosine of the magnetic toolface, wherein Bz is based on Earth's total magnetic field, the cross-axial magnetic field measurement, and Earth's local magnetic dip angle; and
using the azimuth as feedback in the drilling the wellbore.
10. The method of claim 9 , wherein the obtaining the cross-axial magnetic field measurement comprises measuring cross-axial magnetic field with the second magnetometer while rotating the drill bit.
11. The method of claim 9 , wherein the obtaining the cross-axial magnetic field measurement comprises determining a calibrated cross-axial magnetic field measurement using a measurement of a cross-axial magnetic field while static from the second magnetometer and magnitude of x- and y-components of a magnetic field as measured by the first magnetometer and the second magnetometer while static.
12. The method of claim 9 , wherein the point is at the first magnetometer.
13. The method of claim 9 , wherein the first magnetometer and the second magnetometer are on a survey tool.
14. The method of claim 9 , wherein the determining the azimuth is performed downhole, at surface of the wellbore, or a combination thereof.