Abstract: A method involves mixing metallic particles and a liquefied polymer to form a mixture, placing the mixture within a mold, placing a magnet in the vicinity of the mixture within the mold, thereby causing the metallic particles to position themselves in a self-assembly formation within the mixture in response to a magnetic field generated by the magnet, and solidifying the liquefied polymer, such that a polymer matrix is formed. The metallic particles are distributed and secured in the self-assembly formation throughout the polymer matrix, thereby forming a ballast for an untethered downhole tool configured to be lowered into a well formed in a subterranean formation. The polymer matrix is configured to dissolve in response to being exposed to downhole fluid within the well at specified downhole conditions.

Abstract: In an implementation, a downhole robot for oil wells includes a pressure housing enclosing an internal gas-filled or vacuum-filled volume and at least one propulsion unit coupled to an end of the pressure housing. The downhole robot includes at least one centralization element. At least one sensor measures properties of interest with respect to the downhole robot and for an environment outside of the downhole robot. The downhole robot also includes a buoyancy system, an electrical power supply, an anchoring system, and a power system configured for non-contact operation.

Abstract: A method for locating a downhole tool in a wellbore involves obtaining, by the downhole tool, a pressure measurement in the wellbore, generating a first depth estimate based on the pressure measurement, and anticipating a passing of the downhole tool by a collar, based on the first depth estimate and a known depth of the collar. The method further involves, based on the anticipating of the passing of the downhole tool by the collar, performing, by the downhole tool, a collar detection, and based on the collar detection resulting in a detection of the collar: generating an updated depth estimate, and reporting the updated depth estimate.

Abstract: An untethered device includes a tool and a ballast weight. The ballast weight includes an attachment plate that is securable to the tool, a dissolvable ballast, and attachment elements that secure the dissolvable ballast to the attachment plate. At least one of the attachment elements is dissolvable to release the dissolvable ballast from the attachment plate.

Abstract: An untethered device includes a tool and a ballast weight. The ballast weight includes an attachment plate that is securable to the tool, a dissolvable ballast, and attachment elements that secure the dissolvable ballast to the attachment plate. At least one of the attachment elements is dissolvable to release the dissolvable ballast from the attachment plate.

Abstract: An apparatus includes a ballast that is configured to couple to an untethered downhole tool. The ballast includes a composite material. The composite material includes a first portion and a second portion. The first portion includes metallic particles. The first portion is configured to, while the ballast is coupled to the untethered downhole tool, provide weight to the untethered downhole tool to lower the untethered downhole tool into a well formed in a subterranean formation. The second portion includes a polymer matrix. The metallic particles of the first portion are distributed throughout the polymer matrix of the second portion. The second portion is configured to dissolve in response to being exposed to downhole fluid within the well at specified downhole conditions, thereby releasing the metallic particles of the first portions from the polymer matrix that has dissolved.

Abstract: An untethered downhole tool includes a first body, a second body, a logging sensor, a motor, and a controller. Each of the first and second bodies includes a housing that defines an inner volume and a magnetic anchor configured, in an active state, to attach the body to a wellbore tubular. The motor is attached to one of the first or second bodies and coupled to a spooler. The controller is communicably coupled to the motor and the first and second magnetic anchors. The controller is configured to adjust one of the first or second magnetic anchors from the active state to an inactive state; and activate the motor to operate the spooler to spool the cable from the spooler to increase a length of a portion of the cable between the spooler and the detached first or second body.

Abstract: This disclosure discusses methods and apparatus for generating vertical seismic profiles of a subsurface formation though deploying an untethered downhole tool into a wellbore, the untethered tool including at least one seismic sensor, a ballast, and a first electromagnet in the untethered downhole tool to attach the untethered downhole tool to a casing of the wellbore at a predetermined depth. The method further includes transmitting a seismic signal into the subsurface formation from a source located above the subsurface formation, receiving the seismic signal with the at least one seismic sensor, deactivating the first electromagnet to release the untethered downhole tool from the casing of the wellbore, releasing the ballast from the untethered downhole tool such that buoyancy effects move the tool uphole, and retrieving the untethered downhole tool from the wellbore.

Abstract: An untethered downhole tool includes a first body, a second body, a logging sensor, a motor, and a controller. Each of the first and second bodies includes a housing that defines an inner volume and a magnetic anchor configured, in an active state, to attach the body to a wellbore tubular. The motor is attached to one of the first or second bodies and coupled to a spooler. The controller is communicably coupled to the motor and the first and second magnetic anchors. The controller is configured to adjust one of the first or second magnetic anchors from the active state to an inactive state; and activate the motor to operate the spooler to spool the cable from the spooler to increase a length of a portion of the cable between the spooler and the detached first or second body.

Abstract: A downhole tool includes a body configured to move in a wellbore formed from a terranean surface to a subterranean formation in a direction downhole of the terranean surface independent of a downhole conveyance attached to the body; one or more sensors positioned in the body, the one or more sensors configured to measure a value associated with at least one of the wellbore or the terranean surface; and at least one mass positioned in the body and configured to adjust an orientation of the body in response to one or more forces acting on the body as the downhole tool moves in the wellbore in the direction downhole of the terranean surface.

Abstract: An untethered device includes a housing, a magnetic actuator that is coupled to the housing, and a buoyancy device. The buoyancy device includes an attachment plate that is securable to the magnetic actuator, a degradable ballast weight that is coupled to the attachment plate, and a buoyancy-enhancing feature that is positioned adjacent to the attachment plate.

Abstract: An untethered device includes a housing, a magnetic actuator that is coupled to the housing, and a buoyancy device. The buoyancy device includes an attachment plate that is securable to the magnetic actuator, a degradable ballast weight that is coupled to the attachment plate, and a buoyancy-enhancing feature that is positioned adjacent to the attachment plate.

Abstract: An untethered downhole tool includes a first body, a second body, a logging sensor, a motor, and a controller. Each of the first and second bodies includes a housing that defines an inner volume and a magnetic anchor configured, in an active state, to attach the body to a wellbore tubular. The motor is attached to one of the first or second bodies and coupled to a spooler. The controller is communicably coupled to the motor and the first and second magnetic anchors. The controller is configured to adjust one of the first or second magnetic anchors from the active state to an inactive state; and activate the motor to operate the spooler to spool the cable from the spooler to increase a length of a portion of the cable between the spooler and the detached first or second body.

Abstract: A method and a system for collecting data at a fixed point in a wellbore are provided. An exemplary method includes dropping an untethered measurement tool (UMT) in the wellbore, switching a first magnet to drop a ballast from the UMT at a ballast drop condition, switching a second magnet to attach the UMT to a wall of the wellbore at a wall attachment condition. Data is collected in the UMT while the UMT is attached to the wall of the wellbore. The second magnet is switched to release the UMT from the wall of the wellbore at a wall release condition. The UMT is collected from the wellbore and the data is downloaded from the UMT.

Abstract: An untethered downhole tool includes a first body, a second body, a logging sensor, a motor, and a controller. Each of the first and second bodies includes a housing that defines an inner volume and a magnetic anchor configured, in an active state, to attach the body to a wellbore tubular. The motor is attached to one of the first or second bodies and coupled to a spooler. The controller is communicably coupled to the motor and the first and second magnetic anchors. The controller is configured to adjust one of the first or second magnetic anchors from the active state to an inactive state; and activate the motor to operate the spooler to spool the cable from the spooler to increase a length of a portion of the cable between the spooler and the detached first or second body.

Abstract: An apparatus includes a ballast that is configured to couple to an untethered downhole tool. The ballast includes a composite material. The composite material includes a first portion and a second portion. The first portion includes metallic particles. The first portion is configured to, while the ballast is coupled to the untethered downhole tool, provide weight to the untethered downhole tool to lower the untethered downhole tool into a well formed in a subterranean formation. The second portion includes a polymer matrix. The metallic particles of the first portion are distributed throughout the polymer matrix of the second portion. The second portion is configured to dissolve in response to being exposed to downhole fluid within the well at specified downhole conditions, thereby releasing the metallic particles of the first portions from the polymer matrix that has dissolved.

Abstract: Provided here are methods and system to detect an untethered device in a wellhead. The untethered device includes a housing, a transducer, and one or more sensors configured to measure data along the subterranean well. The transducer emits acoustic signals that are received by microphones on the surface of the wellhead. Based on these acoustic signals, the location of the untethered device is determined and appropriate valves may be opened or closed by an operator.

Abstract: A method and a system for collecting data at a fixed point in a wellbore are provided. An exemplary method includes dropping an untethered measurement tool (UMT) in the wellbore, switching a first magnet to drop a ballast from the UMT at a ballast drop condition, switching a second magnet to attach the UMT to a wall of the wellbore at a wall attachment condition. Data is collected in the UMT while the UMT is attached to the wall of the wellbore. The second magnet is switched to release the UMT from the wall of the wellbore at a wall release condition. The UMT is collected from the wellbore and the data is downloaded from the UMT.

Abstract: Techniques for operating a tool include moving a tool in a magnetized tubular member that generates a stationary magnetic field. The tool includes a housing that defines an interior volume, a first magnetic field sensor positioned on or within the housing at a first location, and a second magnetic field sensor positioned on or within the housing at a second location apart from the first location by a separation distance. The techniques further include detecting a first magnetic field amplitude distribution sensed by the first magnetic field sensor started at a first time instant; detecting a second magnetic field amplitude distribution sensed by the second magnetic field sensor started at a second time instant; determining a time difference between the first and second time instants based on the identified magnetic field amplitudes; and determining a speed of the tool based on the separation distance and the time difference.

Abstract: A downhole tool includes a body configured to move in a wellbore formed from a terranean surface to a subterranean formation in a direction downhole of the terranean surface independent of a downhole conveyance attached to the body; one or more sensors positioned in the body, the one or more sensors configured to measure a value associated with at least one of the wellbore or the terranean surface; and at least one mass positioned in the body and configured to adjust an orientation of the body in response to one or more forces acting on the body as the downhole tool moves in the wellbore in the direction downhole of the terranean surface.