Oil-based mud imager with a line source

• US 9,423,524 B2
• Filed: 04/05/2011
• Issued: 08/23/2016
• Est. Priority Date: 04/07/2010
• Status: Active Grant

• Current Assignee: Baker Hughes Incorporated (Baker Hughes Company)
• Original Assignee: Baker Hughes Incorporated (Baker Hughes Company)
• Inventors: Fang, Sheng
• Primary Examiner(s): Assouad, Patrick
• Assistant Examiner(s): PRETLOW, DEMETRIUS R
• Application Number:
  US13/079,948
• Publication Number:
  US 20110248717A1
• Time in Patent Office: 1,967 Days
• Field of Search: 324/355
• US Class Current: 1/1
• CPC Class Codes: G01V 3/24 using ac

Abstract

A resistivity imaging device uses a line source in conjunction with an array of measure electrodes to reduce sensitivity to tool standoff when use in a borehole with oil-based mud.

Claims

1. An apparatus for evaluating an earth formation, the apparatus comprising:

a carrier including an inductively formed line source of electric current configured for capacitive coupling to the earth formation, the carrier configured to be conveyed in a borehole; and

at least one pair of electrodes proximate to a wall of the borehole, a difference in potential between a first one of the at least one pair of electrodes and a second one of the at least one pair of electrodes being indicative of a resistivity property of the earth formation.

2. The apparatus of claim 1 wherein the inductively formed line source of electric current comprises a conductive member and at least one toroidal coil oriented along a longitudinal axis of the borehole, and wherein the inductively formed line source of electric current is further configured to provide current from the conductive member to the formation from locations distributed along the conductive member.

3. The apparatus of claim 2 wherein the at least one pair of electrodes are disposed on a contact member extendable from the carrier.

4. The apparatus of claim 2 wherein the at least one pair of electrodes further comprises an array of electrodes disposed on a contact member extendable from the carrier.

5. The apparatus of claim 4 wherein the line source of current is disposed on the contact member.

6. The apparatus of claim 5 further comprising an additional line source of current disposed on the contact member, the additional line source of current being inclined to the line source of current.

7. The apparatus of claim 1 further comprising a processor configured to use the difference in potential to estimate a value of the resistivity property.

8. The apparatus of claim 7 wherein the at least one pair of electrodes further comprises a first pair of axially separated electrodes and a second pair of electrodes inclined to the first pair of electrodes and wherein the processor is further configured to estimate the value of the resistivity property in two directions.

9. The apparatus of claim 1 further comprising a conveyance device configured to convey the carrier into the borehole, the conveyance device being selected from:

(i) a wireline, (ii) a drillstring, (iii) coiled tubing, and (iv) a slickline.

10. The apparatus of claim 3 further comprising an additional inductively formed line source of current disposed on the contact member;

wherein the carrier comprises a bottom hole assembly, and the conductive member comprises a drill pipe disposed on the bottom hole assembly.

11. A method of evaluating an earth formation, the method comprising:

activating an inductively formed line source of electric current conveyed on a carrier in a borehole, the line source of electric current capacitively coupled to the earth formation; and

providing a first signal from a first one of at least one pair of electrodes proximate to a wall of the borehole indicative of a potential of the first one of the electrodes and a second signal from a second one of the at least one pair of electrodes indicative of a potential of the second one of the electrodes; and

using a processor for estimating a resistivity property of the earth formation using a difference in potential between the first signal and the second signal.

12. The method of claim 11 further comprising using, for the line source of electric current, a conductive member with at least one toroidal coil oriented along a longitudinal axis of the borehole, wherein the inductively formed line source of electric current is further configured to provide current from the conductive member to the formation from locations distributed along the conductive member.