Resistivity logging in sliding mode
Systems and methods for smoothing a resistivity log are disclosed. An azimuthal resistivity tool measures azimuthal impedances at multiple azimuthal angles around a wellbore axis at each depth. It is determined whether the drill string was in a drilling mode or a sliding mode at the depth. If the drill string was in the drilling mode, a co-axial component and a lateral component are determined based in part on the azimuthal impedances associated with the depth and the lateral component is stored. If the drill string was in the sliding mode, a second co-axial component is determined based in part on at least one of the plurality of azimuthal impedances and a previously stored lateral component. The resistivity log is plotted from resistivities determined from the first and second co-axial components at each depth.
1. A method of smoothing a resistivity log, comprising steps:
coupling an azimuthal resistivity tool into a drill string, the azimuthal resistivity tool configured to measure an azimuthal impedance at an azimuthal angle around a wellbore axis;
measuring a plurality of first azimuthal impedances at a respective plurality of azimuthal angles at a depth;
determining whether the drill string was in a drilling mode or a sliding mode while at the depth;
determining, if the drill string was in the drilling mode, a first co-axial component and a lateral component based in part on the plurality of first azimuthal impedances associated with the depth and storing the lateral component;
determining, if the drill string was in the sliding mode, a second co-axial component based in part on at least one of the plurality of first azimuthal impedances and a previously stored lateral component; and
steering a drill bit connected to the drill string based on one of the determined first co-axial component and the lateral component and the determined second co-axial component.
2. The method of claim 1 , wherein at least one lateral component is stored before the step of determining the second co-axial component is performed.
3. The method of claim 1 , wherein:
the plurality of azimuthal angles comprises a predetermined number of azimuthal angles over a complete rotation about the wellbore axis; and
the step of measuring the plurality of first azimuthal impedances comprises recording the measured first azimuthal impedances at the respective predetermined azimuthal angles.
4. The method of claim 3 , wherein:
the step of determining whether the drill string was in the drilling mode or the sliding mode comprises determining a percentage of the predetermined azimuthal angles having a valid measured impedance; and
the drill string was in the sliding mode if the percentage is less than a threshold otherwise the drill string was in the drilling mode.
5. The method of claim 3 , wherein:
the step of determining the second co-axial component comprises selecting the valid measured impedance from the recorded first azimuthal impedances.
6. The method of claim 1 , wherein:
the step of storing the lateral component comprises storing the associated depth.
7. The method of claim 6 , wherein the previously stored lateral component is one of a most-recently stored lateral component and a nearest-depth stored lateral component.
8. The method of claim 7 , further comprising the steps of:
providing, if the drill string was in the drilling mode, the first co-axial component;
providing, if the drill string was in the sliding mode, the second co-axial component.
9. The method of claim 8 , further comprising the step of:
collecting the provided first co-axial components and the second co-axial components and the respective associated depths;
determining a resistivity at each depth based in part of the collected first and second co-axial components; and
creating a drilling log based on the determined resistivities and associated depths.
10. A system for providing a smoothed resistivity log, comprising:
a body configured to be coupled into a drill string disposed in a wellbore having a wellbore axis and comprising a tool axis that is aligned with the wellbore axis when the body is disposed in the wellbore;
an antenna coupled to the body and disposed at a non-zero angle to the tool axis;
an electronics module coupled to the antenna and configured to measure an impedance and provide the measured impedance;
a geosensor configured to provide an azimuthal angle of the antenna about the wellbore axis and a depth;
a processor coupled to the electronics module and to the geosensor; and
a memory coupled to the processor and comprising instructions that, when loaded into the processor and executed, cause the processor to execute steps:
receiving a plurality of impedances and respective azimuthal angles at a respective plurality of depths;
determining whether the drill string was in a drilling mode or a sliding mode at each of the respective plurality of depths;
determining, if the drill string was in the drilling mode, a first co-axial component and a lateral component based in part on the plurality of impedances associated with that depth and storing the lateral component;
determining, if the drill string was in the sliding mode, a second co-axial component based in part on at least one of the plurality of impedances associated with that depth and a previously stored lateral component; and
steering a drill bit connected to the drill string based on one of the determined first co-axial component and the lateral component and the determined second co-axial component.
11. The system of claim 10 , wherein at least one lateral component must be stored before the step of determining the second co-axial component is performed.
12. The system of claim 10 , wherein:
the plurality of azimuthal angles comprises a predetermined number of azimuthal angles over a complete rotation about the wellbore axis; and
the step of measuring the plurality of azimuthal impedances comprises recording the measured first azimuthal impedances at each of the predetermined azimuthal angles.
13. The system of claim 12 , wherein:
the step of determining whether the drill string was in the drilling mode or the sliding mode comprises determining a percentage of the predetermined azimuthal angles having a valid measured impedance; and
the drill string was in the sliding mode if the percentage is less than a threshold otherwise the drill string was in the drilling mode.
14. The system of claim 13 , wherein:
the step of determining the second co-axial component comprises selecting the valid measured impedance from the recorded first azimuthal impedance.
15. The system of claim 10 , wherein the instructions further cause the processor to execute steps:
storing, in association with each depth, either the first co-axial component or the second co-axial component.
16. The system of claim 15 , further comprising the step of:
determining a resistivity at each depth based in part of the collected first and second co-axial components; and
creating a drilling log based on the determined resistivities and associated depths.
17. The system of claim 10 , wherein:
the step of measuring the plurality of first azimuthal impedances is associated with a depth; and
the step of storing the lateral component comprises storing the associated depth.
18. The system of claim 17 , wherein the previously stored lateral component is one of a most-recently stored lateral component and a nearest-depth stored lateral component.
19. A memory comprising instructions that, when loaded into a processor and executed, cause the processor to execute steps:
receiving a plurality of impedances and respective azimuthal angles at a respective plurality of depths;
determining whether the drill string was in a drilling mode or a sliding mode at each of the respective plurality of depths;
determining, if the drill string was in the drilling mode, a first co-axial component and a lateral component based in part on the plurality of impedances associated with each of the respective plurality of depths and storing the lateral component;
determining, if the drill string was in the sliding mode, a second co-axial component based in part on at least one of the plurality of impedances associated with each of the respective plurality of depths and a previously stored lateral component; and
steering a drill bit connected to the drill string based on one of the determined first co-axial component and the lateral component and the determined second co-axial component.
20. The memory of claim 19 , wherein the instructions further cause the processor to execute the step:
determining a resistivity at each depth based in part of the collected first and second co-axial components; and
creating a drilling log based on the determined resistivities and associated depths.