Variable build motor
A variable build motor downhole tool allows changing the build rate in a directional drilling operation without pulling the drill string from the hole and replacing a fixed build sub in the drill string. A pad can be extended upon command to increase the build rate and retracted upon command to decrease the build rate. The pad is mounted on an insert disposed within an outer housing and extends outwardly through the outer housing by action of one or more pistons. Electronics housed in the variable build motor tool are used to receive commands from uphole and cause the pistons to extend, forcing the pad outward to increase the build rate.
1. A downhole tool for use in directional drilling, comprising:
an outer housing having an opening;
an insert disposed within the outer housing, comprising:
an oil chamber filled with oil;
a piston;
a pad disposed radially outward of the piston, wherein extension of the piston urges the pad outward through the opening of the outer housing for engagement with a wellbore and increasing build rate while drilling;
an electric motor, configured to cause extension of the piston; and
circuitry configured to control the electric motor upon receipt of a command received from uphole,
wherein the electric motor allows oil pressure in the oil chamber to increase, responsive to the command, and
wherein the piston urges the pad outward responsive to increased pressure in the oil chamber.
2. The downhole tool of claim 1 , wherein the pad extends outward by rotating about a hinge.
3. The downhole tool of claim 1 , wherein the insert further comprises:
a stop configuring a maximum extension of the pad.
4. The downhole tool of claim 1 , wherein the insert further comprises:
a ball screw assembly, driven by the electric motor; and
a sealing piston configured to seal the oil chamber, driven by the ball screw assembly.
5. The downhole tool of claim 1 , wherein the insert further comprises:
a piston sleeve, wherein the piston is disposed within the piston sleeve.
6. The downhole tool of claim 1 , wherein the command comprises a sequence of changes in rotational speed.
7. The downhole tool of claim 1 , wherein the command comprises a drilling fluid pressure pulse.
8. The downhole tool of claim 1 , wherein the insert further comprises:
a sealed bulkhead between the electric motor and the circuitry; and
a bulkhead carrier affixed to the insert and holding the sealed bulkhead.
9. The downhole tool of claim 1 , wherein the insert further comprises:
a pair of slots on opposite sides of the electric motor; and
an anti-rotation pin configured to prevent the electric motor from rotating within the insert when engaged with one of the pair of slots.
10. A method of changing build rate while directionally drilling, comprising:
receiving by a downhole tool a first command to increase build rate from uphole;
extending a pad outward from the downhole tool responsive to the first command, comprising:
driving a ball screw assembly by an electric motor, responsive to receiving the first command;
opening an oil chamber by the ball screw assembly;
extending a piston outward responsive to opening the oil chamber; and
urging the pad outward by the piston; and
engaging the pad with a wellbore.
11. The method of claim 10 , further comprising:
receiving by the downhole tool a second command to decrease build rate from uphole; and
allowing the pad to retract inward, disengaging the pad from the wellbore responsive to receiving the second command.
12. The method of claim 10 , wherein the first command comprises a variation of rotational speed from a static rotational speed.
13. The method of claim 10 , wherein the first command comprises a drilling fluid pressure pulse.
14. The method of claim 10 , wherein extending the pad outward comprises:
extending a piston responsive to receiving the first command, wherein the piston urges the pad outward.
15. The method of claim 10 , wherein extending the pad outward comprises:
rotating the pad about a hinge on one side of the pad, causing an opposite side of the pad to extend outward.
16. The method of claim 15 , further comprising:
limiting extension of the opposite side by a stop configured for a predetermined maximum extension.
17. The method of claim 10 , further comprising:
stopping pumping of drilling fluid downhole reducing fluid pressure in the downhole tool; and
allowing the pad to retract inward responsive to reducing fluid pressure in the downhole tool.
18. The method of claim 10 , further comprising:
maintaining extension of the pad while drilling.