# US 2008/0186805 A1 · Apparatus and method for determining drilling fluid acoustic properties

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- Number: US 2008/0186805 A1
- Document ID: US20080186805A1
- Status: Published application
- Kind: A1
- Application number: 11/701,260
- Filed: 2007-02-01
- Published: 2008-08-07
- Earliest claimed: 2007-02-01
- Assignees: PathFinder Energy Services, Inc.
- Inventors: Wei Han
- Web page: https://patentgrep.com/patent/US20080186805A1

## CPC

- E21B 47/01: Devices for supporting measuring instruments on drill bits, pipes, rods or wirelines; Protecting measuring instruments in boreholes against heat, shock, pressure or the like
- E21B 47/085: using radiant means, e.g. acoustic, radioactive or electromagnetic
- E21B: EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS

## Abstract

Aspects of this invention include a downhole tool having first and second radially offset ultrasonic standoff sensors and a controller including instructions to determine at least one of a drilling fluid acoustic velocity and a drilling fluid attenuation coefficient from the reflected waveforms received at the standoff sensors. The drilling fluid acoustic velocity may be determined via processing the time delay between arrivals of a predetermined wellbore reflection component at the first and second sensors. The drilling fluid attenuation coefficient may be determined via processing amplitudes of the predetermined wellbore reflection coefficients. The invention advantageously enables the acoustic velocity and attenuation coefficient of drilling fluid in the borehole annulus to be determined in substantially real-time.

## Claims

### Claim 1

A downhole measurement tool, comprising:
a substantially cylindrical tool body having a cylindrical axis;
first and second radially offset standoff sensors deployed on the tool body, each of the standoff sensors configured to (i) transmit an ultrasonic pressure pulse into a borehole and (ii) receive a reflected waveform; and
a controller including instructions for determining at least one of (i) a drilling fluid acoustic velocity and (ii) a drilling fluid attenuation coefficient from the reflected waveforms received at the first and second standoff sensors.

### Claim 2 (depends on 1)

The downhole measurement tool of claim 1, wherein:
the tool body is configured for coupling with a drill string; and
the measurement tool further comprises at least one logging while drilling sensor.

### Claim 3 (depends on 2)

The downhole measurement tool of claim 2, wherein the logging while drilling sensor comprises at least one nuclear density sensor.

### Claim 4 (depends on 1)

The downhole measurement tool of claim 1, wherein the first and second standoff sensors are radially offset the distance in the range from about 0.25 to about 0.5 inches.

### Claim 5 (depends on 1)

The downhole measurement tool of claim 1, wherein the first and second standoff sensors are longitudinally offset a distance of less than about 1 foot.

### Claim 6 (depends on 1)

The downhole measurement tool of claim 1, wherein the first and second standoff sensors are deployed at substantially the same circumferential position on the tool body.

### Claim 7 (depends on 1)

The downhole measurement tool of claim 1, wherein:
the controller includes instructions for determining the drilling fluid acoustic velocity from an arrival time delay of a predetermined portion of the reflected waveforms between the first and second standoff sensors; and
the controller includes instructions for determining the drilling fluid attenuation coefficient from amplitudes of predetermined portions of the reflected waveforms received at each of the first and second standoff sensors.

### Claim 8 (depends on 1)

The downhole measurement tool of claim 1, wherein the controller is configured to determine the drilling fluid acoustic velocity according to the following equation:
c
f
=
2

L
2
-
2

L
1
T
2
-
T
1
≈
2

L
0
Δ


T
wherein cf represents the drilling fluid acoustic velocity, L1 and L2 represent standoff distances at the first and second standoff sensors, L0 represents a radial offset distance between the first and second standoff sensors, T1 and T2 represent arrival times of wellbore reflection components received at the first and second standoff sensors, and ΔT represents a difference between the arrival times.

### Claim 9 (depends on 1)

The downhole measurement tool of claim 1, wherein the controller is configured to determine the drilling fluid attenuation coefficient according to at least one equation selected from the group consisting of:
α
=
1
2

(
L
2
-
L
1
)

(
ln

(
V
1

b
V
2

b
)
-
ln

(
K
1
K
2
)
)
=
1
2

(
L
2
-
L
1
)

ln

(
V
1

b

K
2
V
2

b

K
1
)
;
α
=
1
2

(
L
2
-
L
1
)

(
ln

(
V
1

b
V
2

b
)
-
ln

(
V
1

i
V
2

i
)
)
=
1
2

(
L
2
-
L
1
)

ln

(
V
1

b

V
2

i
V
2

b

V
1

i
)
;
and
α
=
1
2

L
0

(
ln

(
V
1

b
V
2

b
)
-
ln

(
V
1

i
V
2

i
)
)
=
1
2

L
0

ln

(
V
1

b

V
2

i
V
2

b

V
1

i
)
wherein α represents the drilling fluid attenuation coefficient, L1 and L2 represent standoff distances at the first and second standoff sensors, L0 represents a radial offset distance between the first and second standoff sensors, K1 and K2 represent characteristic parameters of the corresponding first and second standoff sensors, V1i and V2i represent amplitudes of interface reflection components received at the corresponding first and second standoff sensors, and V1b and V2b represent amplitudes of wellbore reflection components received at the corresponding first and second standoff sensors.

### Claim 10

A logging while drilling tool comprising:
a substantially cylindrical logging while drilling tool body including at least one stabilizer;
first and second longitudinally spaced nuclear density sensors deployed on the stabilizer;
first and second radially offset standoff sensors deployed on the tool body; each of the standoff sensors configured to (i) transmit an ultrasonic pressure pulse into a borehole and (ii) receive a reflected waveform; and
a controller including instructions for determining at least one of (i) a drilling fluid acoustic velocity and (ii) a drilling fluid attenuation coefficient from the reflected waveforms received at the first and second standoff sensors.

### Claim 11 (depends on 10)

The logging while drilling tool of claim 10, wherein the first and second standoff sensors are deployed on corresponding first and second step down sections such that each of the standoff sensors is radially recessed from the nuclear density sensors.

### Claim 12 (depends on 10)

The logging while drilling tool of claim 10, wherein the first and second standoff sensors and to the first and second nuclear density sensors are deployed at substantially the same circumferential position on the tool body.

### Claim 13

A method for determining an acoustic velocity of drilling fluid in a borehole, the method comprising:
(a) transmitting first and second acoustic signals in a borehole utilizing corresponding first and second radially offset transducers;
(b) receiving first and second reflected signals at the corresponding first and second transducers from corresponding first and second acoustic signals transmitted in (a);
(c) determining a time delay between a predetermined wellbore reflection component of the corresponding first and second reflected signals received in (b); and
(d) processing the time delay determined in (c) to determine the acoustic velocity of the drilling fluid.

### Claim 14 (depends on 13)

The method of claim 13, wherein the acoustic velocity is substantially proportional to a radial offset distance between the first and second transducers.

### Claim 15 (depends on 13)

The method of claim 13, wherein the acoustic velocity is substantially inversely proportional to the time delay determined in (c).

### Claim 16 (depends on 13)

The method of claim 13, wherein the acoustic velocity of the drilling fluid is determined in (d) according to the equation:
c
f
=
2

L
2
-
2

L
1
T
2
-
T
1
≈
2

L
0
Δ


T
wherein cf represents the acoustic velocity of the drilling fluid, L1 and L2 represent standoff distances at the first and second transducers, L0 represents a radial offset distance between the first and second transducers, T1 and T2 represent arrival times of the predetermined wellbore reflection components received at the first and second standoff sensors, and ΔT represents the time delay.

### Claim 17 (depends on 13)

The method of claim 13, further comprising:
(e) determining first and second amplitudes of a wellbore reflection component of the corresponding first and second reflected signals received in (b); and
(f) processing the first and second amplitudes determined in (e) to determine an attenuation coefficient of the drilling fluid.

### Claim 18 (depends on 13)

The method of claim 13, wherein the transducers are further (i) axially offset and (ii) circumferentially aligned in the borehole.

### Claim 19 (depends on 13)

The method of claim 13, wherein the first and second transducers are deployed on a logging while drilling tool.

### Claim 20 (depends on 13)

The method of claim 13, further comprising:
(e) comparing a plurality of the time delays determined in (c); and
(f) determining the acoustic velocity in (d) only when a deviation of the time delays compared in (e) is less than a predetermined threshold.

### Claim 21

A method for determining an attenuation coefficient of drilling fluid in a borehole, the method comprising:
(a) transmitting first and second acoustic signals in a borehole utilizing corresponding first and second radially offset transducers;
(b) receiving first and second reflected signals at the corresponding first and second transducers from corresponding first and second acoustic signals transmitted in (a);
(c) determining an amplitude of a first predetermined component of each of the corresponding first and second reflected signals received in (b); and
(d) processing the amplitudes determined in (c) to determine the attenuation coefficient of the drilling fluid.

### Claim 22 (depends on 21)

The method of claim 21, wherein the attenuation coefficient is substantially inversely proportional to a radial offset distance between the first and second transducers.

### Claim 23 (depends on 21)

The method of claim 21, wherein the attenuation coefficient is substantially proportional to a logarithm of a ratio of the amplitudes determined in (c).

### Claim 24 (depends on 21)

The method of claim 21, wherein:
(c) further comprises determining an amplitude of a second predetermined component of each of the corresponding first and second reflected signals received in (b).
(d) further comprises processing the amplitudes of the first and second predetermined components to determine the attenuation coefficient.

### Claim 25 (depends on 24)

The method of claim 24, wherein the first predetermined component of each of the reflected signals is a wellbore reflection echo and the second predetermined component of each of the reflected signals is an interface reflection echo.

### Claim 26 (depends on 21)

The method of claim 21, wherein the attenuation coefficient of the drilling fluid is determined in (d) according to at least one equation selected from the group consisting of:
α
=
1
2

(
L
2
-
L
1
)

(
ln

(
V
1

b
V
2

b
)
-
ln

(
K
1
K
2
)
)
=
1
2

(
L
2
-
L
1
)

ln

(
V
1

b

K
2
V
2

b

K
1
)
;
α
=
1
2

(
L
2
-
L
1
)

(
ln

(
V
1

b
V
2

b
)
-
ln

(
V
1

i
V
2

i
)
)
=
1
2

(
L
2
-
L
1
)

ln

(
V
1

b

V
2

i
V
2

b

V
1

i
)
;
and
α
=
1
2

L
0

(
ln

(
V
1

b
V
2

b
)
-
ln

(
V
1

i
V
2

i
)
)
=
1
2

L
0

ln

(
V
1

b

V
2

i
V
2

b

V
1

i
)
wherein α represents the attenuation coefficient of the drilling fluid, L1 and L2 represent standoff distances at the first and second transducers, L0 represents a radial offset distance between the first and second transducers, K1 and K2 represent characteristic parameters of the corresponding first and second transducers, V1i and V2i represent amplitudes of interface reflection components received at the corresponding first and second transducers, and V1b and V2b represent amplitudes of wellbore reflection components received at the corresponding first and second standoff sensors.

### Claim 27 (depends on 21)

The method of claim 21, wherein the transducers are further (i) axially offset and (ii) circumferentially aligned in the borehole.

### Claim 28 (depends on 21)

The method of claim 21, further comprising:
(e) determining a time delay between a predetermined wellbore reflection component of the corresponding first and second reflected signals received in (b); and
(f) processing the time delay determined in (e) to determine an acoustic velocity of the drilling fluid.

### Claim 29 (depends on 21)

The method of claim 21, wherein the first and second transducers are deployed on a logging while drilling tool.

### Claim 30

A method for determining an acoustic velocity and an attenuation coefficient of drilling fluid in a borehole, the method comprising:
(a) transmitting first and second acoustic signals in a borehole utilizing corresponding first and second radially offset transducers;
(b) receiving first and second reflected signals at the corresponding first and second transducers from the corresponding first and second acoustic signals transmitted in (a);
(c) determining a time delay between a predetermined wellbore reflection component of the corresponding first and second reflected signals received in (b);
(d) determining an amplitude of the predetermined wellbore reflection components of the corresponding first and second reflected signals received in (b); and
(e) processing the time delay and the amplitudes determined in (c) and (d) to determine the acoustic velocity and the attenuation coefficient of the drilling fluid.

### Claim 31 (depends on 30)

The method of claim 30, wherein:
(d) further comprises determining an amplitude of an interface reflection component of each of the corresponding first and second reflected signals received in (b); and
(e) further comprises processing the time delay determined in (c), the amplitudes of the predetermined wellbore reflection components determined in (d), and the amplitudes of the interface reflection components determined in (d) to determine the acoustic velocity and the attenuation coefficient of the drilling fluid.

### Claim 32

A method for estimating a local roughness of a subterranean borehole wall, the method comprising:
(a) transmitting first and second acoustic signals in a borehole utilizing corresponding first and second radially offset transducers;
(b) receiving first and second reflected signals at the corresponding first and second transducers from corresponding first and second acoustic signals transmitted in (a);
(c) determining a transit time delay between wellbore reflection components of the first and second reflected signals received in (b);
(d) repeating (a), (b), and (c) a plurality of times; and
(e) processing the time delays determined in (c) to determine a time delay deviation, the time delay deviation being a measure of the borehole roughness such that increasing deviations indicate increasing roughness values.