Downhole vibration energy harvester for low power applications
A method including drilling a wellbore using a drill bit connected to a drill string. The drill string includes a vibrational energy harvester and a tool disposed inside a casing of the drill string. The vibrational energy harvester includes a stator including a conductive coil, and a rotor including magnets disposed outside the conductive coil. The rotor is unpowered. The rotor is free to rotate outside the conductive coil, and the rotor is unattached to other components of the drill string. The method also includes generating vibrations in the drill string by engaging the drill bit to a bottom of the wellbore. The method also includes harvesting electricity generated in the stator as the rotor rotates in response to the vibrations. The method also includes supplying, via an electrical connection between the stator and the tool, the electricity to the tool.
1 . A method comprising:
drilling a wellbore using a drill bit connected to a drill string, wherein the drill string comprises a vibrational energy harvester and a tool disposed inside a casing of the drill string, the vibrational energy harvester comprising:
a stator comprising a conductive coil;
a rotor comprising a plurality of magnets disposed outside the conductive coil, wherein the rotor is unpowered and the rotor is free to rotate outside the conductive coil;
a first bearing disposed proximate a first axial end of the rotor; and
a second bearing disposed proximate a second axial end of the rotor, wherein the rotor is supported for free axial movement between the first bearing and the second bearing, and wherein the first bearing and the second bearing constrain a boundary of axial movement of the rotor;
generating vibrations in the drill string by engaging the drill bit to a bottom of the wellbore;
harvesting electricity generated in the stator as the rotor rotates in response to the vibrations; and
supplying, via an electrical connection between the stator and the tool, the electricity to the tool.
2 . The method of claim 1 , wherein the rotor is disposed in a fluid disposed within the drill bit.
3 . The method of claim 1 , wherein the stator comprises a first cylinder and the rotor comprises a second cylinder coaxial with the first cylinder.
4 . The method of claim 1 , wherein harvesting comprises harvesting an alternating current.
5 . A system to harvest downhole energy, comprising:
a first element disposed on a drill string, the first element including conductive coils;
a second element suspended outside the first element, the second element including a plurality of permanent magnets, the second element suspended in a viscous fluid;
a first bearing disposed proximate a first end of the second element; and
a second bearing disposed proximate a second end of the second element,
wherein the second element is supported for free axial movement between the first bearing and the second bearing, and wherein the first bearing and the second bearing constrain a boundary of axial movement of the second element,
wherein movement of the drill string causes torsional oscillations of the second element,
wherein current is induced in the conductive coils due to a changing magnetic field.
6 . The system of claim 5 , wherein the first element comprises a stator and the second element comprises a rotor.
7 . The system of claim 6 , wherein the first element is coaxial to the second element.
8 . The system of claim 5 , wherein the plurality of permanent magnets are disposed radially around an inner surface of the second element and are further disposed in an alternating pole arrangement.
9 . The system of claim 5 , wherein the system further comprises a drill bit connected to the drill string,
wherein the first element and the second element are disposed inside the drill string.
10 . The system of claim 5 , further comprising:
a tool connected to the drill string and electrically connected to the first element.
11 . The system of claim 10 , wherein the tool is electrically unattached to another source of electrical power.
12 . The system of claim 5 , wherein:
the first element comprises a hollow cylinder and an electrically conducting coil oriented axially along a surface of the hollow cylinder; and
the second element comprises a second cylinder in which the plurality of permanent magnets are embedded.
13 . A device comprising:
a drill string comprising a casing and a drill bit;
a tool disposed inside the casing of the drill string, the tool comprising an electrical connection and an electrically powered mechanism; and
a vibrational energy harvester connected to the drill string and electrically connected to the electrical connection, wherein the vibrational energy harvester comprises:
a stator comprising a conductive coil, the stator being fixedly coupled to the drill string such that the stator rotates with the drill string during a drilling operation;
a rotor comprising a plurality of magnets disposed outside the conductive coil, wherein the rotor is unpowered and the rotor is free to rotate outside the conductive coil;
a first bearing disposed proximate a first axial end of the rotor; and
a second bearing disposed proximate a second axial end of the rotor,
wherein the rotor is supported for free axial movement between the first bearing and the second bearing, and wherein the first bearing and the second bearing constrain a boundary of axial movement of the rotor.
14 . The device of claim 13 , wherein the tool comprises a wellbore monitoring device.
15 . The device of claim 13 , wherein:
the stator comprises a hollow cylinder and an electrically conducting coil oriented axially along a surface of the hollow cylinder; and
the rotor comprises a second cylinder in which is embedded the plurality of magnets.
16 . The device of claim 15 , wherein the plurality of magnets are oriented axially along the rotor, and wherein the plurality of magnets are disposed around an inside surface of the rotor in an alternating pole arrangement.
17 . The device of claim 13 , wherein the rotor is suspended and free to rotate within a viscous fluid.
18 . The device of claim 17 , wherein vibrations generated by engagement of the drill bit with a bottom of a wellbore during the drilling operation cause the rotor to oscillate relative to the stator, thereby inducing an alternating electrical current in the conductive coil.