Method and apparatus for azimuthal electromagnetic well logging using shielded antennas

• US 6,191,586 B1
• Filed: 06/10/1998
• Issued: 02/20/2001
• Est. Priority Date: 06/10/1998
• Status: Expired due to Term

• Current Assignee: Halliburton Energy Services Incorporated (Halliburton Company)
• Original Assignee: Dresser Industries Incorporated (Halliburton Company)
• Inventors: Bittar, Michael S.
• Primary Examiner(s): Patidar, Jay
• Assistant Examiner(s): Andersen, Henry S.
• Application Number:
  US09/095,523
• Time in Patent Office: 986 Days
• Field of Search: 324/338, 324/339, 324/343, 324/346, 324/356, 324/369, 324/375, 324/366, 324/340, 324/341, 324/342, 324/344, 324/345, 324/347
• US Class Current: 324/339
• CPC Class Codes: G01V 3/28 using induction coils

Abstract

An apparatus and method for implementing azimuthal capabilities on electromagnetic wave resistivity well logging tools. The apparatus comprises a structurally simple antenna shield positioned around either the transmitting or receiving antennas, or both, positioned on the well logging tool on the drill string. The shields partially surround the tool and provide an electromagnetic barrier for either the transmission or reception of electromagnetic waves, as the case may be. Positioned on the shield are appropriately placed and sized windows through which electromagnetic waves may either be transmitted or received, depending upon the function of the antenna that the shield surrounds. Variations in window dimensions allow optimization of the device for use in conjunction with a variety of formations and a variety of drill mud characteristics.

Claims

1. An improved well logging tool for making azimuthally sensitive resistivity measurements within a formation surrounding a drill string positioned within a borehole, said improved well logging tool comprising:

at least one transmitting antenna positioned on said drill string within said borehole, said transmitting antenna for generating a primary electromagnetic field within said surrounding formation, thereby inducing currents to flow within said formation which in turn generate a secondary electromagnetic field within said formation, said borehole, and said drill string;

at least one receiving antenna positioned on said drill string, in spaced relationship with said transmitting antenna, said receiving antenna for measuring characteristics of said secondary electromagnetic field through induction of a current within said receiving antenna indicative of said characteristics;

at least one conductive shield associated with said drill string in a manner as to partially shield said transmitting antenna or said receiving antenna or both;

wherein said conductive shield defines a window through which said primary electromagnetic field may be generated or said secondary electromagnetic field may be detected by said transmitting or receiving antennas.

2. The improved well logging tool of claim 1 wherein said at least one conductive shield comprises:

a conductive shield positioned on said at least one transmitting antenna.

3. The improved well logging tool of claim 1 wherein said at least one conductive shield comprises:

a conductive shield positioned on said at least one receiving antenna.

4. The improved well logging tool of claim 1 wherein said at least one conductive shield comprises:

a first conductive shield partially shielding said at least one transmitting antenna; and

a second conductive shield partially shielding said at least one receiving antenna.

5. The improved well logging tool of claim 1 wherein said at least one conductive shield defines a window having an opening in the range of approximately 30°

to approximately 90°

.

6. The improved well logging tool of claim 1 wherein said at least one conductive shield defines a window having an opening in the range of approximately 90°

to approximately 180°

.

7. The improved well logging tool of claim 1 wherein said at least one transmitting antenna and said at least one receiving antenna comprise wire coils positioned concentrically around a longitudinal axis of said tool.

8. An improved well logging tool for making azimuthally sensitive resistivity measurements within a formation surrounding a drill string positioned within a borehole, said improved well logging tool comprising:

a plurality of transmitting antenna coils positioned on said drill string, said transmitting antenna coils for generating primary electromagnetic fields within said surrounding formation, thereby inducing currents to flow within said formation which in turn generate secondary electromagnetic fields within said formation, said borehole, and said drill string;

a plurality of receiving antenna coils positioned on said drill string in spaced relationship with said transmitting antenna coils and with each other, said plurality of receiving antenna coils for measuring characteristics of said secondary electromagnetic fields through induction of a current within said receiving antenna coils indicative of said characteristics;

a conductive shield positioned on said drill string in such a manner as to partially shield at least one of said transmitting antenna coils; and

a conductive shield positioned on said drill string in such a manner as to partially shield at least one of said receiving antenna coils;

wherein said conductive shields define windows through which said primary electromagnetic fields may be generated or said secondary electromagnetic fields may be detected by said transmitting or receiving antennas.

9. The improved well logging tool of claim 8 wherein said conductive shield partially shielding at least one of said transmitting antenna coils is oriented in a first azimuthal direction, and said conductive shield partially shielding at least one of said antenna coils is also oriented in said first azimuthal direction.

10. The improved well logging tool of claim 8 wherein said conductive shield partially shielding at least one of said transmitting antenna coils is oriented in a first azimuthal direction and said conductive shield partially shielding at least one of said receiving antenna coils is oriented in a second azimuthal direction, said second azimuthal direction differing from said first azimuthal direction by at least 90°

.

11. The improved well logging tool of claim 10 wherein said second azimuthal direction differs from said first azimuthal direction by approximately 180°

.

12. An improved method for well logging, the improvement being a method for making azimuthally sensitive resistivity measurements within a formation surrounding a drill string positioned within a borehole, said improved method comprising the steps of:

positioning at least one transmitting antenna coil on said drill string;

directing a current to flow within said transmitting antenna coil so as to generate a primary electromagnetic field within said surrounding formation, thereby inducing currents to flow within said formation which currents in turn generate a secondary electromagnetic field within said formation, said borehole, and said drill string;

positioning at least one receiving antenna coil on said drill string in spaced relationship with said at least one transmitting antenna coil;

positioning at least one conductive shield over said transmitting antenna coil or said receiving antenna coil, said conductive shield defining at least one window through which said secondary electromagnetic field may be detected by said receiving antenna coil or said primary electromagnetic field may be generated by said transmitting antenna coil;

measuring characteristics of said secondary electromagnetic field through induction of a current within said receiving antenna coil indicative of said characteristics; and

orienting said at least one window of said conductive shield in plurality of azimuths and repeating said step of measuring characteristics of said secondary electromagnetic fields at each of said azimuths.

13. The improved method for well logging of claim 12 wherein:

said step of positioning at least one receiving antenna coil on said drill string comprises positioning first and second receiving antenna coils in first and second positions on said drill string;

said step of positioning at least one transmitting antenna coil on said drill string comprises positioning a first transmitting antenna coil in a third position on said drill string and a second transmitting antenna coil in a fourth position on said drill string; and

wherein a mid point between said first and second positions on said drill string is displaced a first distance from said third position on said drill string and a second distance from said fourth position on said drill string, said second distance being greater than said first distance, wherein a combination of said first transmitting antenna coil and said first and second receiving antenna coils provides a first depth of investigation into said surrounding formation, and a combination of said second transmitting antenna coil with said first and second receiving antenna coils provides a second depth of investigation into said surrounding formation, said second depth of investigation being greater than said first depth of investigation.

14. The improved method for well logging of claim 12 wherein:

said step of positioning at least one receiving antenna coil on said drill string comprises positioning first and second receiving antenna coils in first and second positions on said drill string;

said step of positioning at least one transmitting antenna coil on said drill string comprises positioning a first transmitting antenna coil in a third position on said drill string, a second transmitting antenna coil in a fourth position on said drill string, and a third transmitting antenna coil in a fifth position on said drill string; and

wherein a mid point between said first and second positions on said drill string is displaced a first distance from said third position on said drill string, a second distance from said fourth position on said drill string and a third distance from said fifth position on said drill string, said third distance being greater than said second distance and said second distance being greater than said first distance, wherein a combination of said first transmitting antenna coil and said first and second receiving antenna coils provides a first depth of investigation into said surrounding formation, a combination of said second transmitting antenna coil with said first and second receiving antenna coils provides a second depth of investigation into said surrounding formation, and a combination of said third transmitting antenna coil with said first and second receiving antenna coils provides a third depth of investigation into said surrounding formation, said third depth of investigation being greater than said second depth of investigation and said second depth of investigation being greater than said first depth of investigation.

15. The improved method for well logging of claim 12 wherein:

said step of positioning at least one receiving antenna coil on said drill string comprises positioning first and second receiving antenna coils in first and second positions on said drill string;

said step of positioning at least one transmitting antenna coil on said drill string comprises positioning a first transmitting antenna coil in a third position on said drill string, a second transmitting antenna coil in a fourth position on said drill string, a third transmitting antenna coil in a fifth position on said drill string, and a fourth transmitting antenna coil in a sixth position on said drill string; and

wherein a mid point between said first and second positions on said drill string is displaced a first distance from said third position on said drill string, a second distance from said fourth position on said drill string, a third distance from said fifth position on said drill string, and a fourth distance from said sixth position on said drill string, said fourth distance being greater than said third distance, said third distance being greater than said second distance, and said second distance being greater than said first distance wherein a combination of said first transmitting antenna coil and said first and second receiving antenna coils provides a first depth of investigation into said surrounding formation, a combination of said second transmitting antenna coil with said first and second receiving antenna coils provides a second depth of investigation into said surrounding formation, a combination of said third transmitting antenna coil with said first and second receiving antenna coils provides a third depth of investigation into said surrounding formation, and a combination of said fourth transmitting antenna coil with said first and second receiving antenna coils provides a fourth depth of investigation into said surrounding formation, said fourth depth of investigation being greater than said third depth of investigation, said third depth of investigation being greater than said second depth of investigation, and said second depth of investigation being greater than said first depth of investigation.

16. The improved method for well logging of claim 12 wherein said step of positioning at least one conductive shield comprises positioning a first conductive shield over at least one transmitting antenna coil in a first azimuthal direction and positioning a second conductive shield over at least one receiving antenna coil also in said first azimuthal direction.

17. The improved method for well logging of claim 12 wherein said step of positioning at least one conductive shield comprises positioning a first conductive shield over at least one transmitting antenna coil in a first azimuthal direction and positioning a second conductive shield over at least one receiving antenna coil in a second azimuthal direction, said first azimuthal direction differing from said second azimuthal direction by at least 90°

.

18. The improved method for well logging of claim 12 wherein said step of positioning at least one conductive shield comprises positioning a conductive shield defining a plurality of windows through which electromagnetic waves may be received by said receiving antenna coils or propagate from said transmitting antenna coils, said plurality of windows being directed in a plurality of distinct azimuths.