System and methods for measuring borehole caliper in oil-based mud

Patent metadata

Field	Value
Publication number	US-10415951-B2
Application number	US-201214366682-A
Country	US
Kind code	B2
Filing date	Dec 20, 2012
Priority date	Dec 23, 2011
Publication date	Sep 17, 2019
Grant date	Sep 17, 2019

Abstract

Systems and methods for estimating standoff and/or caliper in a wellbore for oil-based mud drilling are provided. The systems include a sensor having a primary electrode and at least two secondary electrodes, and an electronics subsystem having a controller and a processor for driving the system and correlating current measurements with standoff and/or caliper. The electrodes are positioned relative to one another such that there is a distinct flow of current between the primary electrode and each secondary electrode. In operation, a single excitation frequency is applied to the primary electrode and a simultaneous measurement of current flowing between the primary electrode and each secondary electrode is obtained. Standoff is estimated from the measurements. The estimations can be independent of formation properties when an appropriate excitation frequency is used.

First claim

What is claimed is:

1. A system, comprising:
a. a downhole tool positionable in a borehole;
b. at least one sensor disposed on the tool, the at least one sensor comprising: a primary electrode and two or more secondary electrodes, wherein the electrodes are arranged to provide a distinct current measurement between the primary electrode and each secondary electrode when the system is in operation; and,
c. an electronics subsystem comprising a controller and a processor and including machine-readable instructions for: exciting the primary electrode with a single frequency and maintaining the primary electrode at a first potential and the secondary electrodes at a second potential different from the first potential; simultaneously measuring current flow through each secondary electrode; and estimating a standoff between the tool and the borehole, a borehole caliper, or both from the current flow measurements, wherein the estimation comprises calculating a value of a ratio ma associated to a a th secondary electrode according to the formula:

ma
=



I
⁢

⁢
1

+
…
+
In

I
⁢

⁢
a



,

wherein n identifies the number of electrodes, “a” identifies the secondary electrode and is greater than 1,
wherein I 1 is the current flowing between the primary electrode and the first secondary electrode, I 2 is the current flowing between the primary electrode and the second secondary electrode, In is the current flowing between the primary electrode and the n th secondary electrode, Ia is the current flowing between the primary electrode and the a th secondary, and wherein the estimation further includes correlating the value ma to the standoff in view of a calibration curve.

2. The system according to claim 1 , wherein the electrodes are arranged in a concentric pattern and the primary electrode is centered in the pattern.

3. The system according to claim 1 , wherein the electrodes are arranged in a non-concentric pattern and the primary electrode is positioned at one end of the pattern.

4. The system according to claim 1 , wherein the at least one sensor is at least two sensors, further wherein a first sensor of the at least two sensors and a second sensor of the at least two sensors are positioned at the same height on the tool about 180 degrees apart.

5. The system according to claim 1 , wherein the downhole tool has a diameter and the at least one sensor is a first sensor and a second sensor, and the electronics subsystem estimates the borehole caliper by summing a first standoff estimated from measuring current flow through the first sensor with a second standoff estimated from measuring current flow through the second sensor taking into account the downhole tool diameter.

6. The system according to claim 1 , wherein the tool is a logging while drilling tool or a measurement while drilling tool.

7. A method, comprising:
a. positioning a downhole tool having at least one sensor disposed thereon in a borehole, wherein the at least one sensor comprises a primary electrode and two or more secondary electrodes;
b. applying a single exciting frequency to the primary electrode while maintaining the primary electrode at a first potential and the secondary electrodes at a second potential different from the first potential;
c. simultaneously obtaining measurements of current flow between the primary electrode and each secondary electrode; and
d. estimating a standoff between the tool and the borehole, a borehole caliper, or both from the measurements, wherein the estimation comprises calculating a value of a ratio ma associated to a a th secondary electrode according to the formula:

ma
=



I
⁢

⁢
1

+

I
⁢

⁢
2

+

…
⁢

⁢
In

Ia



,

wherein n identifies the number of electrodes, “a” identifies the secondary electrode and is greater than 1,
wherein I 1 is the current flowing between the primary electrode and the first secondary electrode, I 2 is the current flowing between the primary electrode and the second secondary electrode, In is the current flowing between the primary electrode and the n th secondary electrode, Ia is the current flowing between the primary electrode and the a th secondary electrode, and wherein the estimation further includes correlating the value ma to the standoff in view of a calibration curve.

8. The method according to claim 7 , wherein step d comprises estimating the caliper from measurements of current flow in a first sensor and a second sensor that are positioned at the same height on the tool about 180 degrees apart from each other.

9. The method according to claim 7 , wherein the excitation frequency ranges from about 1 kHz to less than 100 kHz.

10. The method according to claim 7 , wherein the electrodes are arranged in a concentric pattern with the primary electrode centered in the pattern or in a non-concentric pattern with the primary electrode positioned at one end of the pattern.

11. The method according to claim 7 , wherein the standoff, the caliper, or both are measured while drilling.

12. The system of claim 1 , wherein at least two of the secondary electrodes are of an identical size.

Assignees

• Schlumberger Technology Corp

Inventors

• Legendre Emmanuel

Classifications

• E21B47/26

  Storing data down-hole, e.g. in a memory or on a record carrier · CPC title

• G01B7/14 Primary

  for measuring distance or clearance between spaced objects or spaced apertures (G01B7/30 takes precedence) · CPC title

• G01B7/13

  Internal diameters · CPC title

• E21B47/08

  Measuring diameters or related dimensions at the borehole · CPC title

• E21B47/10

  Locating fluid leaks, intrusions or movements · CPC title