Surface excited downhole ranging using relative positioning
A downhole relative positioning system utilizes electromagnetic and survey measurements from a first well to calibrate a formation model, which is then used to improve the interpretation of measurements from a second well. Since the methods described herein utilize a differential approach, even though the exact position of each wellbore may not be accurately identified, their relative positions can be accurately identified.
1. A method for downhole ranging, comprising:
obtaining first measurement signals in a first wellbore;
obtaining second measurement signals in a second wellbore;
calculating a relative measurement between the first and second measurement signals;
determining a position of the second wellbore relative to the first wellbore using the relative measurement; and
using the relative measurement to perform downhole ranging.
2. A method as defined in claim 1 , wherein calculating the relative measurement comprises calculating a differential measurement between the first and the second measurement signals.
3. A method as defined in claim 2 , wherein calculating the relative measurement further comprises calculating a ratio of the differential measurement to the first or second measurement signals.
4. A method as defined in claim 1 , wherein calculating the relative measurement further comprises calculating a ratio of:
the first measurement signal to the second measurement signal; or
the second measurement signal to the first measurement signal.
5. A method as defined in claim 1 , wherein determining the position of the second wellbore comprises performing an inversion using survey data from the first or second wellbores.
6. A method as defined in claim 2 , wherein determining the position of the second wellbore comprises performing an inversion using:
survey data from the first or second wellbores; and
a ratio of the differential measurement to the first or second measurement signals.
7. A method as defined in claim 5 , wherein performing the inversion comprises performing the inversion using a ratio of:
the first measurement signal to the second measurement signal; or
the second measurement signal to the first measurement signal.
8. A method as defined in claim 1 , wherein:
obtaining the first measurement signal comprises:
deploying a first sensor along the first wellbore;
emitting a first source signal toward the first wellbore; and
measuring the first source signal using the first sensor, thereby acquiring the first measurement signal; and
obtaining the second measurement signal comprises:
deploying a second sensor along the second wellbore;
emitting a second source signal toward the second wellbore; and
measuring the second source signal using the second sensor, thereby acquiring the second measurement signal.
9. A method as defined in claim 1 , wherein obtaining the first and second measurement signals comprises emitting a source signal toward the first and second wellbores using a surface excitation source.
10. A method as defined in claim 1 , wherein obtaining the first and second measurement signals comprises acquiring bi-axial or triaxial measurement signals.
11. A method as defined in claim 1 , wherein:
the first measurement signal is obtained using a first sensor; and
the second measurement signal is obtained using the first sensor at a different time.
12. A method as defined in claim 1 , wherein:
the first measurement signal is obtained using a first sensor; and
the second measurement is obtained using a second sensor.
13. A method as defined in claim 12 , wherein the first and second sensors are calibrated using a same excitation source.
14. A method as defined in claim 1 , wherein obtaining the first and second measurement signals comprise at least one of acquiring absolute, phase, or real or imaginary measurements.
15. A method as defined in claim 1 , wherein the first and second measurement signals are obtained using a sensor deployed on a bottom hole assembly.
16. A method as defined in claim 15 , further comprising steering the bottom hole assembly deployed along the second wellbore using the determined position of the second wellbore.
17. A method as defined in claim 1 , further comprises avoiding the first wellbore using the determined position of the second wellbore.