Dynamic borehole azimuth measurements

Patent metadata

Field	Value
Publication number	US-9273547-B2
Application number	US-201113323116-A
Country	US
Kind code	B2
Filing date	Dec 12, 2011
Priority date	Dec 12, 2011
Publication date	Mar 1, 2016
Grant date	Mar 1, 2016

Abstract

A method for making dynamic borehole azimuth measurements while drilling includes processing cross-axial magnetic field measurements in combination with accelerometer measurements to compute the dynamic borehole azimuth. In one or more embodiments, the cross-axial magnetic field measurements and the accelerometer measurements may be used to compute the magnitude of a cross-axial magnetic field component, a toolface offset, and a borehole inclination, which may in turn be used to compute the dynamic borehole azimuth. The disclosed methods may utilize near-bit sensor measurements obtained while drilling, thereby enabling a near-bit dynamic borehole azimuth to be computed while drilling.

First claim

What is claimed is:

1. A method for making a dynamic borehole azimuth measurement while rotating a downhole measurement tool in a borehole, the method comprising:
(a) rotating a downhole tool in the borehole, the downhole tool including a cross-axial magnetic field sensor and an axial accelerometer;
(b) obtaining a set of cross-axial magnetic field measurements and a set of axial accelerometer measurements while the downhole tool is rotating in (a);
(c) processing the set of cross-axial magnetic field measurements obtained in(b) to compute a magnitude of a cross-axial magnetic field component; and
(d) processing the magnitude of the cross axial magnetic field component computed in (c) and the set of axial accelerometer measurements obtained in (b) to compute the dynamic borehole azimuth, wherein the dynamic borehole azimuth is computed in (d) according to the following equation:

cos
⁢

⁢
Azi

=

B
2

-

B
xy
2

B

-

A
z

G

⁢
sin
⁢

⁢
D

sin
⁡

[

arccos
⁡

(

A
z

D

)

]

⁢
cos
⁢

⁢
D

wherein Azi represents the dynamic borehole azimuth, B xy represents the magnitude of the cross-axial magnetic field component computed in (c), A z represents an axial accelerometer measurement, G represents the magnitude of the earth's local gravitational field, B represents the magnitude of the earth's local magnetic field, and D represents the local magnetic dip angle.

2. The method of claim 1 , wherein (c) further comprises:
(i) processing the set of cross-axial magnetic field measurements to obtain a magnitude of a periodic variation; and
(ii) setting the magnitude of the cross-axial magnetic field component equal to the magnitude of the periodic variation obtained in (i).

3. The method of claim 1 , wherein (c) further comprises:
(i) processing a first set of cross-axial magnetic field measurements with respect to a second set of cross-axial magnetic field measurements to obtain a radius of a circle or ellipse; and
(ii) setting the magnitude of the cross-axial magnetic field component equal to the radius determined in (i).

4. The method of claim 1 , wherein the magnitude of the cross-axial magnetic field component is computed in (c) according to at least one of the following equations:

B

X
⁢

⁢
Y

=

B
x
2

+

B
y
2

;

B
XY

=

2
·

σ

B
⁢

⁢
x

·

σ

B
⁢

⁢
y

;

Σ
⁡

[

B

x
⁢

⁢
c

2

+

B
yc
2

-

B

x
⁢

⁢
y

]

2

wherein B xy represents the magnitude of the cross-axial magnetic field component, B x and B y represent first and second cross-axial magnetic field measurements made along x- and y-axes, σ Bx and σ By represent standard deviations of a first set of B x measurements and a second set of B y measurements made over several complete rotations of the downhole tool;
and B xc and B yc represent corrected B x and B y measurements after corrections have been applied.

5. The method of claim 1 , wherein (c) further comprises:
(i) processing the set of cross-axial magnetic field measurements and the set of cross-axial accelerometer measurements to obtain a m

Assignees

• Brooks Andrew G
• Sugiura Junichi
• Schlumberger Technology Corp

Inventors

• Brooks Andrew G
• Sugiura Junichi

Classifications

• E21B47/022 Primary

  of the borehole, e.g. using geomagnetism · CPC title