Formation resistivity measurement sensor contained onboard a drill bit (resistivity in bit)

• US 20040104726A1
• Filed: 06/16/2003
• Published: 06/03/2004
• Est. Priority Date: 04/18/2001
• Status: Active Grant

• Current Assignee: Baker Hughes Incorporated (Baker Hughes Company)
• Original Assignee: Baker Hughes Incorporated (Baker Hughes Company)
• Inventors: Chemali, Roland E., Ritter, Rene N., Makohl, Friedhelm, Evans, Martin Townley, Pastusek, Paul, Hewitt, Stanley T.
• Granted Patent: US 6,850,068 B2
• Time in Patent Office: Days
• US Class Current: 324/369
• CPC Class Codes: E21B 47/013 Devices specially adapted for supporting measuring instruments on drill bits
• CPC Class Codes: E21B 47/024 of devices in the borehole determining slope or direction of the borehole E21B47/022
• CPC Class Codes: G01V 3/24 using ac
• CPC Class Codes: G01V 3/28 using induction coils
• CPC Class Codes: Y02A 90/30 Assessment of water resources

Abstract

A method and apparatus for obtaining a resistivity measurement of an earth formation surrounding a borehole in an MWD device uses an electrode for injecting current into the earth formation and an electrode for obtaining a responsive signal from the borehole. The electrodes are located on the drill bit arm or blade. Measured resistivity values are obtained at the location of the drill bit. Measurements can be taken in both oil-based mud and water-based mud environments. Maximum or minimum resistivity can be used to best represent the resistivity of the surrounding formation.

Claims

1. An apparatus for making measurements of a parameter of interest of an earth formation during the drilling of a borehole therein, the apparatus comprising:

(a) a drill bit conveyed on a bottom hole assembly for drilling the borehole;

(b) at least one measure electrode carried on an exterior surface of the drillbit for conveying a measure current into the formation; and

(c) a device set in a cavity on the drillbit responsive to least one of (i) the current in the at least one measure electrode, and, (ii) a voltage of the at least one measure electrode, said device producing a measure signal indicative of the resistivity.

2. The apparatus of claim 1 further comprising a source of current coupled to the at least one electrode, said source of current located within said cavity on the drillbit.

3. The apparatus of claim 1 wherein the drillbit has a profile for providing a specified minimum standoff from a borehole wall.

4. The apparatus of claim 1 wherein said at least one electrode further comprises a first electrode and a second electrode, the apparatus further comprising:

(i) a source of current for producing a measure current in said first electrode, and

(ii) a measuring device for measuring said measure current and measuring a voltage of said second electrode with respect to a remote reference.

5. The apparatus of claim 1 wherein said borehole includes a substantially nonconducting fluid, and wherein said measure current has a frequency selected to capacitively couple said measure electrode to said earth formation.

6. The apparatus of claim 1 further comprising a processor for determining said signal based on one of (i) a maximum value of said current, and, (ii) a minimum value of said current.

7. The apparatus of claim 1 further comprising at least one additional sensor on said drillbit for providing a measurement of an additional parameter of interest of the earth formation, said at least one additional sensor selected from the group consisting of (i) a temperature sensor, and, (ii) a pressure sensor,

8. A method determining a resistivity of an earth formation during the drilling of a borehole, the method comprising:

(i) conveying a drill bit on a bottom hole assembly into a borehole

(ii) using at least one measure electrode on an outer surface of said drill bit to inject a measure current into the formation; and

(iii) producing a measure signal indicative of said resistivity based in part on said measure current.

9. The method of claim 8 further comprising selecting said drillbit to provide a specified minimum standoff from a wall of the borehole.

10. The method of claim 8 wherein producing said measure signal further comprises using a value of the measure current selected from the group consisting of (i) a minimum value of said measure current, and, (ii) a maximum value of said measure current.

11. The method of claim 8, wherein producing said measure signal further comprises using a voltage measurement.

12. The method of claim 8, wherein said at least one electrode further comprises a first electrode and a second electrode and wherein producing said measure signal further comprises using a voltage measurement of the second electrode.

13. The apparatus of claim 8, wherein said borehole includes a substantially non-conducting fluid, and wherein said measure current has a frequency selected to capacitively couple said measure electrode to said earthy formation.

14. The method of claim 8 further comprising obtaining an additional measurement by using an additional sensor selected from the group consisting of (i) a temperature sensor, and, (ii) a pressure sensor on the drill bit, as an early kick indicator.

15. The method of claim 14 further comprising using said additional measurement is a kick indicator.