Gradient-based single well ranging system for SAGD application
A tool, method and system for ranging between two wellbores. The target wellbore includes a conductive member disposed within a portion of the target wellbore. An investigative wellbore includes an electromagnetic gradiometer positioned within the wellbore, as well as emitter electrode and return electrode spaced apart along an investigative wellbore, preferably in the process of being drilled. The position of the emitter electrode and the return electrode are selected to optimize current transmission to the target wellbore in order to enhance the electromagnetic field emanating from the conductive member at a desired point along the conductive member. Where the electrodes and gradiometer are carried by a drill string, gap subs are positioned along the drill string to minimize conduction of current along the drill string therebetween. In some embodiments, the gradiometer is positioned between the emitter and return electrodes.
1. A wellbore ranging system for electromagnetic ranging between first and second wellbores, the system comprising:
a drill string or tubing string coupled to a bottom hole assembly (BHA) comprising:
an electric current source removably affixed to the BHA;
at least two electrodes removably affixed along the BHA axis, where at least one electrode is an emitter electrode and at least one electrode is a return electrode, wherein the electric current source is electrically connected to the emitter electrode; and
a magnetic gradiometer removably affixed along the BHA axis, configured to detect a magnetic gradient induced by a current flowing in a conductive member in one of the wellbores.
2. The system of claim 1 , wherein the emitter and return electrodes are spaced apart from each other along the BHA axis.
3. The system of claim 1 , further comprising at least three electrodes and at least two insulators, wherein the at least three electrodes are electrically isolated from one another along the BHA by the at least two insulators.
4. The system of claim 1 , wherein the emitter and return electrodes are separated by at least one insulator.
5. The system of claim 1 , wherein the magnetic gradiometer is separated from the electrodes by at least one insulator.
6. The system of claim 1 , further comprising a third electrode, wherein the third electrode is an emitter electrode spaced apart from the other emitter electrode.
7. The system of claim 1 , further comprising a third electrode, wherein the third electrode is a return electrode spaced apart from the other return electrode.
8. The system of claim 1 , wherein the magnetic gradiometer comprises at least three dipoles arranged radially spaced apart from one another about the BHA axis.
9. The system of claim 1 , wherein the magnetic gradiometer comprises at least four dipoles arranged radially spaced apart from one another about the BHA axis.
10. The system of claim 1 , wherein the magnetic gradiometer comprises at least six dipoles arranged radially spaced apart from one another about the BHA axis.
11. The system of claim 1 , wherein the magnetic gradiometer comprises at least eight dipoles arranged radially spaced apart from one another about the BHA axis.
12. The system of claim 1 , wherein the magnetic gradiometer comprises:
a first pair of dipoles symmetrically arranged around a central axis and spaced apart from one another; and
a second pair of dipoles arranged around the central axis and spaced apart from one another, wherein the second pair of electrodes are rotated about the central axis at a radial angle of between 0-89° relative to the first pair of electrodes.
13. The system of claim 12 , wherein the first pair of dipoles are disposed at a first diameter around the central axis and the second pair of dipoles are disposed at a second diameter, different than the first diameter, about the central axis.
14. The system of claim 1 , wherein the magnetic gradiometer comprises:
a first pair of dipoles symmetrically arranged around a central axis and spaced apart from one another; and
a second pair of dipoles arranged around the central axis and spaced apart from one another, wherein a relative angle of between 0-89° is formed between the first and second pair of electrodes.
15. The system of claim 14 , wherein the first pair of dipoles are disposed at a first diameter around the central axis and the second pair of dipoles are disposed at a second diameter, different than the first diameter, about the central axis.
16. The system of claim 15 , wherein the second pair of dipoles are rotated about the central axis at a radial angle of between 0-89° relative to the first pair of dipoles.
17. The system of claim 16 , wherein the first pair of dipoles is disposed at a first diameter around the central axis and the second pair of dipoles is disposed at a second diameter, different than the first diameter, about the central axis.
18. The system of claim 1 , further comprising a first insulator and a second insulator disposed along the BHA axis, wherein the emitter electrode is separated from the return by the first insulator and one of the emitter or receiver electrodes is separated from the magnetic gradiometer by the second insulator.
19. The system of claim 18 , further comprising a third electrode and a third insulator disposed along the BHA axis, wherein the third electrode is electrically isolated from the other electrodes by the third insulator.
20. The system of claim 1 , further comprising:
an insulator disposed between the emitter electrode and the magnetic gradiometer, insulating the magnetic gradiometer from current flow from the emitter electrode along the BHA; and
an insulator disposed between the emitter and the return electrodes, insulating the return electrode from current flow from the emitter electrode along the BHA.
21. The system of claim 1 , wherein the magnetic gradiometer is disposed along the axis of the BHA between the emitter electrode and the return electrode.
22. The system of claim 21 , further comprising:
an insulator disposed between the emitter electrode and the magnetic gradiometer, insulating the magnetic gradiometer from current flow from the emitter electrode along the BHA; and
an insulator disposed between the return electrode and the magnetic gradiometer, insulating the magnetic gradiometer from current flow from the return electrode along the BHA.
23. The system of claim 1 , further comprising an elongated conductive member disposed in a portion of one wellbore and the BHA disposed in the other wellbore.
24. The system of claim 1 , further comprising a drill string, wherein the BHA is carried by the drill string, the system further comprising a drill bit and a steering module carried by the drill string.
25. The system of claim 1 , further comprising:
a first insulator disposed along the axis between the emitter and the return electrodes, insulating the return electrode from current flow from the emitter electrode along the BHA; and
a second insulator disposed along the axis on the opposite side of the return electrode from first insulator.
26. A wellbore ranging method comprising:
drilling a first wellbore and positioning an elongated conductive member within a portion of the first wellbore;
commencing the drilling of a second wellbore;
positioning a return electrode along a pipe string in the second wellbore;
positioning an emitter electrode along a pipe string in the second wellbore and electrically insulating the emitter electrode from the return electrode on the pipe string;
activating an alternating current and delivering the alternating current to the emitter electrode;
utilizing the emitter electrode to generate a magnetic field from the first wellbore; and
measuring an absolute magnetic field and a gradient magnetic field from the second wellbore based on the magnetic field generated from the first wellbore, where the combination of both the absolute magnetic field values and gradient magnetic field values are used to determine the distance and direction of the conductive member positioned in the first wellbore relative to the second wellbore.
27. The method of claim 26 , further comprising positioning a gap sub along the pipe string between the emitter electrode and the return electrode.
28. The method of claim 26 , further comprising positioning a gap sub along the pipe string between the emitter electrode and an EM sensor utilized to measure magnetic gradient.
29. The method of claim 26 , further comprising positioning along the pipe string an EM sensor utilized to measure magnetic gradient between the return electrode and the emitter electrode.
30. The method of claim 29 , further comprising positioning a gap sub along the pipe string between the emitter electrode and an EM sensor and positioning a gap sub along the pipe string between the return electrode and an EM sensor.
31. The method of claim 29 , wherein the step of utilizing comprises transmitting current to the emitter electrode.
32. The method of claim 29 , wherein the step of measuring comprises collecting magnetic field data, calculating a magnetic field gradient, and calculating a distance and direction between the first and second wells based on the magnetic field gradient.