Buoyancy Control of Robots Downhole
Untethered, downhole robots are described. In some cases, the downhole robots are configured to have a density within + or −20% of wellbore fluid in which it will be operating. In some cases, the downhole robots a controller capable of discerning deviation of the wellbore from vertical and, in response, control a buoyancy system to change longitudinal distribution of the weight of the robot, wherein the magnitude of the change in the longitudinal distribution of the weight suffices to reorient the robot.
1 . An untethered, downhole robot is configured to have a density within + or −20% of wellbore fluid in which it will be operating, the downhole robot comprising:
a generally elongate housing;
at least one propulsion unit on an end of the housing on the longitudinal axis;
a sensor system configured to sense structural information regarding geometry of a wellbore, determine position and orientation of the robot in the wellbore, and collect measurements characterizing the wellbore fluids and reservoir characteristics;
a controller coupled to receive the sensed structural information and wellbore fluid information to control the robot's traversal within the wellbore; and
a memory device to log collected data locally on robot.
2 . The downhole robot of claim 1 , further comprising:
a buoyancy system configured to change the longitudinal distribution of weight of the robot is present to aid with vertical descent and ascent when the robot is not sufficiently neutrally buoyant; and
a controller capable of discerning deviation of the wellbore from vertical and, in response, control the buoyancy system to change longitudinal distribution of the weight of the robot, wherein the magnitude of the change in the longitudinal distribution of the weight suffices to reorient the robot.
3 . The downhole robot of claim 2 , wherein, in response to discernment of the deviation during descent of the robot into the wellbore, the controller is configured to control the buoyancy system to change the longitudinal distribution of the weight of the robot such that a bow of the robot is made less dense, a stern of the robot is made more dense, or densities of both the bow and the stern are changed.
4 . The downhole robot of claim 2 , wherein the controller is configured to regulate a lateral direction of the reorientation of the robot that occurs responsive to the changed longitudinal distribution of weight.
5 . The downhole robot of claim 4 , wherein the robot further comprises a steering mechanism coupled to the controller, wherein the controller is configured to regulate the lateral direction of the reorientation of the robot using the steering mechanism.
6 . The downhole robot of claim 4 , wherein:
the downhole robot further includes an orientation sensor configured to sense an orientation of the robot; and
the controller coupled to receive the sensed orientation information from the orientation sensor and to regulate the lateral direction of the reorientation based thereon.
7 . The downhole robot of claim 2 , wherein:
the downhole robot comprises a density sensor configured to sense density of a downhole fluid surrounding the downhole robot; and
the controller is further configured to control the buoyancy system to change the longitudinal distribution of the weight of the robot based on the sensed density of the downhole fluid.
8 . The downhole robot of claim 2 , wherein the buoyancy system is a multi-chamber, internal buoyancy system that conveys liquid between chambers without communicating fluid with surroundings of the downhole robot.
9 . The downhole robot of claim 2 , wherein the buoyancy system is configured to communicate fluid with surroundings of the downhole robot.
10 . The downhole robot of claim 2 , wherein:
the buoyancy system is configured to change lateral distribution of weight of the robot; and
the controller is configured to control the changes in the lateral distribution of the weight based on the sensed structural information.
11 . The downhole robot of claim 1 , further comprising three or more protruding members distributed around the housing, wherein the protruding members are configured to contact an inner wall of a wellbore that is being traversed while preventing the housing from contacting the inner wall.
12 . A method of navigating a wellbore with a downhole robot, the method performed by a controller of the downhole robot and comprising:
detecting, using a sensor located on the downhole robot, approach of the downhole robot to a deviation of the wellbore from vertical; and
in response to the detection of the approach of the deviation, changing longitudinal distribution of weight of the downhole robot, wherein the change in the longitudinal distribution of the weight suffices reorient the downhole robot.
13 . The method of claim 11 , wherein changing the longitudinal distribution of weight of the downhole robot comprises causing a bow of the downhole robot to descend slower than a stern of the downhole robot.
14 . The method of claim 11 , further comprising controlling a direction of the lateral reorientation of the downhole robot.
15 . The method of claim 13 , wherein controlling the direction of the lateral reorientation of the downhole robot comprises controlling
a rudder, or
a hydroplane, or
a drag-generating components, or
a steerable propeller, or
a lateral redistribution of weight of the downhole robot.
16 . The method of claim 14 , wherein controlling the direction of the lateral reorientation of the downhole robot comprises sensing an orientation of the downhole robot and using the sensed orientation to control the direction of the lateral reorientation of the downhole robot.
17 . The method of claim 14 , wherein changing the longitudinal distribution of weight of the downhole robot comprises moving a fluid bow-ward or stern-ward between chambers housed in the robot.
18 . The method of claim 14 , wherein changing the longitudinal distribution of weight of the downhole robot comprises communicating a fluid with a surroundings of the downhole robot.
19 . The method of claim 14 , further comprising guiding the downhole robot into a sidewall of the wellbore prior to changing the longitudinal distribution of the weight of the downhole robot.
20 . The method of claim 14 , further comprising guiding the downhole robot into a sidewall of the wellbore prior to changing the longitudinal distribution of the weight of the downhole robot.
21 . The method of claim 14 , further comprising:
detecting, using the sensor, approach of the downhole robot to a lateral section of the wellbore; and
in response to the detection of the approach of the lateral section, generating thrust to propel the downhole robot.
22 . The method of claim 14 , wherein:
the method further comprises sensing a density of downhole fluid surrounding the downhole robot; and
the longitudinal distribution of weight of the downhole robot is changed based on the sensed density.
23 . A method of navigating a wellbore with an untethered autonomous downhole robot that has a density within + or −20% of wellbore fluid in which it will be operating, the method performed by a controller of the downhole robot and comprising:
detecting, using a sensor located on the downhole robot, approach of the downhole robot to a deviation of the wellbore from vertical; and
in response to the detection of the approach of the deviation, exclusively driving the robot with a propulsion unit, the driving including traversing a portion of the wellbore and passively reorienting the robot via guidance from geometry of the wellbore.
24 . The method of claim 23 , wherein the robot comprises:
sensors configured to measure wellbore geometry, wellbore fluid information, reservoir characteristics; and
sensors configured to measure speed of the robot, depth of the robot, angular rate of the robot, attitude of the robot, and/or acceleration of the robot.
25 . The method of claim 23 , further comprising:
determining, by the controller of the downhole robot, position of the robot within the wellbore; and
determining, by the controller of the downhole robot, orientation of the robot within the wellbore.
26 . The method of claim 23 , further comprising:
operating a stern-mounted thruster and a bow-mounted thruster to generate thrust in both a forward direction and in a reverse direction.
27 . The method of claim 26 , further comprising:
operating the stern-mounted thruster and the bow-mounted thruster at different speeds to roll the robot.
28 . The method of claim 23 , wherein the downhole robot further comprises three or more protruding members distributed around the housing, wherein passively reorienting the downhole robot comprises contacting an inner wall of a wellbore with at least one of the protruding members while preventing the housing from contacting the inner wall.
29 . The method of claim 23 further comprising:
adjusting, by the controller of the downhole robot, an orientation of the robot using the propulsion unit.