METHOD AND DEVICE FOR DETECTING DAMAGE RATE OF AN INNER COATING OF A DOWNHOLE OIL CASING

• US 20180209928A1
• Filed: 03/21/2018
• Published: 07/26/2018
• Est. Priority Date: 09/25/2015
• Status: Active Grant

• Current Assignee: Petrochina Company Limited (China National Petroleum Corporation)
• Original Assignee: Petrochina Company Limited (China National Petroleum Corporation)
• Inventors: LI, Qiongwei, CHENG, Bihai, TANG, Zewei, XUE, Jianqiang, FU, Caili, YANG, Huili, HE, Zhiwu, YANG, Lihua, ZHANG, Xinzhu, SUN, Yulai
• Granted Patent: US 10,641,723 B2
• Time in Patent Office: Days
• CPC Class Codes: E21B 17/1078 Stabilisers or centralisers for casing, tubing or drill pipes devices for off-center positioning E21B17/10; E21B17/1007 - E21B17/1064 take precedence
• CPC Class Codes: E21B 47/007 Measuring stresses in a pipe string or casing for locating blocked portions of pipes E21B47/09
• CPC Class Codes: E21B 47/092 by detecting magnetic anomalies
• CPC Class Codes: G01N 27/041 of a solid body
• CPC Class Codes: G01N 27/205 in insulating materials

Abstract

This disclosure provides a method and device for detecting the damage rate of an inner coating of a downhole oil casing. The method includes filling the oil casing with electrolyte, obtaining the well depth-detection current on a discharge electrode in a process of moving the discharge electrode from one end of the oil casing to the other end of the oil casing, and determining a well depth-damage rate state of the inner coating of the oil casing according to the well depth-detection current. This application can realize quantitative judgment for the damage rate of an inner coating of a downhole oil casing, resulting in rapid in detection speed, convenient and safe in operation, and low detection cost.

Claims

1. A method for detecting the damage rate of an inner coating of a downhole oil casing, the method comprising:

filling an oil casing with electrolyte;

obtaining a well depth-detection current on a discharge electrode in a process of moving the discharge electrode from one end of the oil casing to the other end of the oil casing; and

determining a well depth-damage rate state of the inner coating of the oil casing according to the well depth-detection current.

2. The method according to claim 1, wherein prior to the step of determining the well depth-damage rate state of the inner coating of the oil casing according to the well depth-detection current, the method further comprises:

obtaining a function relationship between an experimental current of the inner coating of a sample pipe and the known damage rate of the inner coating of the sample pipe by experiments.

3. The method according to claim 2, wherein after the step of obtaining the function relationship between the experimental current of the inner coating of the sample pipe and the known damage rate of the inner coating of the sample pipe by experiments, the method further comprises:

obtaining a well depth-inner coating damage rate curve of the inner coating of the oil casing according to the well depth-detection current data and the function relationship.

4. The method according to claim 1, wherein a calculation formula of the well depth-detection current I is as follows:

5. The method according to claim 1, wherein the discharge electrode has a moving speed of less than 1,000 m/h.

6. The method according to claim 1, wherein the electrolyte is surface water or mixed water of the surface water and formation water, and the conductivity of the electrolyte is less than 2,000 μ

s/cm.

7. The method according to claim 1, wherein the discharge electrode is an inert and inactive metal ring of an outer guide wire, the two end surfaces and an inner ring surface of the inert and inactive metal ring are coated with an insulating coating, and a distance from an outer ring surface of the inert and inactive metal ring to an inner surface of the oil casing is less than 0.02 m.

8. The method according to claim 1, wherein the material of the oil casing is carbon steel and the material of the inner coating of the oil casing is organic insulating coating.

9. A device for detecting the damage rate of an inner coating of a downhole oil casing comprising:

a constant voltage source;

a ground electrode connected with the constant voltage source;

a discharge electrode connected with the constant voltage source, moving from one end of an oil casing to the other end of the oil casing;

electrolyte injected into the oil casing; and

a dynamic logging system connected with the discharge electrode via a logging cable for acquiring a well depth-detection current.

10. The device according to claim 9, further comprising a centralizer connected with the discharge electrode via the logging cable for maintaining the discharge electrode always at the center of the oil casing.

11. The device according to claim 9, further comprising a magnetic locator disposed between the discharge electrode and the centralizer for obtaining positions of a coupling and a short casing of the oil casing, so as to position the discharge electrode.

12. The device according to claim 9, further comprising an insulating shield disposed on the discharge electrode for fixing the discharge electrode, shielding the loop current and diverting the electrolyte.

13. The device according to claim 9, further comprising a weight bar disposed between the discharge electrode and the centralizer for enabling the logging cable to be in a straighten state, so that the centralizer move smoothly within the oil casing.

14. The device according to claim 9, further comprising a bridle disposed between the discharge electrode and the dynamic logging system for converting logging connectors and detecting the operation safety.

15. The device according to claim 9, further comprising a conductivity electrode disposed between the discharge electrode and the bridle for detecting the conductivity of the electrolyte, so as to obtain conductivity parameters required when preparing the experimental electrolyte in calibration experiments.

16. The device according to claim 9, wherein when the inner coating of the oil casing is intact, a current loop is formed between the discharge electrode and the ground electrode through the electrolyte and the oil casing;

and

when the inner coating of the oil casing in the area adjacent to the discharge electrode is damaged, a current loop is formed between the discharge electrode and the ground electrode through the electrolyte, the damages of the inner coating of the oil casing and the oil casing.