Downhole gradiometric ranging utilizing transmitters and receivers having magnetic dipoles

1. A method for downhole ranging, the method comprising:

drilling a first wellbore, the first wellbore comprising an elongated conductive body;

deploying at least two magnetic dipole transmitters and at least four magnetic dipole receivers in a second wellbore;

inducing a current along the first wellbore using the transmitters that results in a magnetic field being emitted from the first wellbore;

receiving the magnetic field utilizing the receivers, wherein a gradient field is measured in a radial direction along the second wellbore; and

utilizing the gradient field to thereby determine a distance between the first and second wellbores.

2. A method as defined in claim 1 , further comprising determining a direction of the first wellbore in relation to the second wellbore, wherein determining the direction comprises:

determining a total field of the received magnetic field;

determining an angle between x and y components of the total field; and

utilizing the angle to determine the direction.

3. A method as defined in claim 1 , further comprising utilizing the gradient field to determine a direction of the first wellbore in relation to the second wellbore.

4. A method as defined in claim 3 , wherein determining the direction further comprises:

determining an angle between orthogonal components of the gradient field; and

utilizing the angle to determine the direction.

5. A method as defined in claim 1 , wherein determining the distance between the first and second wellbores further comprises eliminating a direct signal emitted from the transmitters.

6. A method as defined in claim 5 , wherein the elimination of the direct signal comprises:

calculating a magnetic field of the transmitters at the receivers; and

subtracting the calculated magnetic field from the received magnetic field.

7. A method as defined in claim 5 , wherein the elimination of the direct signal comprises utilizing at least four bucking receivers to cancel an imaginary component of the direct signal.

8. A method as defined in claim 3 , wherein the at least four receivers are two pairs of magnetic dipole receivers, and determining the distance and direction further comprises:

radially positioning two receivers of the pairs in opposite directions in relation to a measurement center in the second wellbore; and

determining the gradient field in a desired direction by calculating a difference between magnetic fields at each receiver of the pairs.

9. A method as defined in claim 1 , wherein:

the first wellbore is a producer well; and

the second wellbore is an injector well,

wherein the method is utilized in a Steam Assisted Gravity Drainage operation.

10. A method as defined in claim 1 , wherein:

the first wellbore is a blow out well; and

the second wellbore is a relief well.

11. A method as defined in claim 1 , wherein the transmitters and receivers are deployed along a drilling assembly, logging assembly or wireline assembly, the receivers being radially positioned around a body of the drilling, logging or wireline assembly.

12. A method as defined in claim 1 , further comprising steering a drilling assembly deployed along the second wellbore using the determined distance between the first and second wellbores.

13. A method as defined in claim 12 , further comprises avoiding the first wellbore using the distance determination.

14. A downhole ranging system comprising processing circuitry to implement the method in claim 1 .

15. A downhole ranging assembly, comprising:

a bottom hole assembly comprising:

at least two magnetic dipole transmitters; and

at least four magnetic dipole receivers radially positioned around an axis of the bottom hole assembly; and

processing circuitry to implement a method comprising:

inducing a current along a first wellbore using the transmitters that results in a magnetic field being emitted from the first wellbore;

receiving the magnetic field utilizing the receivers, wherein a gradient field is measured in a radial direction along the bottom hole assembly; and

utilizing the gradient field to thereby determine a distance between the first and second wellbores.

16. A downhole ranging assembly as defined in claim 15 , further comprising four bucking receivers positioned along the bottom hole assembly between the transmitters and receivers.

17. A downhole ranging assembly as defined in claim 16 , wherein the bucking receivers comprise an opposite polarization in relation to the receivers.

18. A downhole ranging assembly as defined in claim 15 , wherein the bottom hole assembly is a drilling, wireline, or logging assembly.

19. A downhole ranging assembly as defined in claim 15 , wherein:

the transmitters are positioned in non-parallel relationship to one another along the bottom hole assembly;

the receivers are radially separated in a direction perpendicular to the axis of the bottom hole assembly; and

a magnetic moment of the receivers is oriented in a direction perpendicular to both the axis of the bottom hole assembly and the direction of radial separation.

20. A downhole ranging assembly as defined in claim 15 , further comprising eight receivers positioned radially around the body of the bottom hole assembly at 45 degree intervals.

21. A downhole ranging assembly as defined in claim 15 , wherein the transmitters and receivers comprise at least one of a coil, solenoid, or magnetometer.