Systems and methods for measuring flow velocity of a fluid mixture in a lateral section of an oil/gas well are presented. The flow velocity is measured by tracking movement of particles and/or features in the fluid mixture via visible and/or infrared imaging sensors of a camera-based flow sensor. According to another aspect, the imaging sensors detect back-reflected light by the particles and/or features, the light emitted by illuminators in the visible and/or infrared spectrum. According to yet another aspect, the particles are quantum dot illuminators injected into the fluid mixture, the flow velocity based on a time-of-flight of the quantum dots. The camera-based flow sensor may be rotatable to measure flow velocities at different angular positions of a pipe, rotation provided by rotation of an element of a mobile vessel to which the flow sensor is rigidly coupled.

A downhole tool has a tool body with an outer diameter equal to a borehole diameter, at least one cavity formed in and opening to an outer surface defining the outer diameter of the tool body, a light source, a filter, and a light detector mounted in the at least one cavity, and a window disposed at the opening of the at least one cavity, wherein the window encloses the cavity.

In a drill bit which has hard-faced cutting or gauge protection elements positioned to be in direct contact with subterranean formation as the bit is rotated, at least one of these elements includes a window positioned to be in direct contact with the formation or cuttings from the formation as the bit rotates and moves forward to drill into the formation. Electromagnetic radiation with wavelength in the range from 100 nm to 2600 nm is transmitted through the window to the formation in contact with the window. Electromagnetic radiation such as fluorescence that returns through the same window is received by a spectrometer. The source and receiver of electromagnetic radiation are both accommodated within the downhole drilling equipment but spaced from the windowed element. The electromagnetic radiation travels along light guides from the source to the window and from the window to the receiver.

A downhole tool has a tool body with an outer diameter equal to a borehole diameter, at least one cavity formed in and opening to an outer surface defining the outer diameter of the tool body, a light source, a filter, and a light detector mounted in the at least one cavity, and a window disposed at the opening of the at least one cavity, wherein the window encloses the cavity.

A well tool can include a well tool housing and a cooling section positioned within the well tool housing, the cooling section including a helical cooling fluid flow path, and the flow path having a reversal of direction proximate an end of the cooling section. Another well tool can include a cooling fluid which flows through the helical flow path toward the end of the cooling section in one direction, and which flows through the helical flow path away from the end of the cooling section in an opposite direction. Another well tool can include the cooling fluid which flows through the helical flow path, and which makes multiple passes longitudinally through the cooling section proximate a heat-sensitive device.

A system, in certain embodiments, includes an SMA thermostat. The SMA thermostat includes a body, a sleeve, a biasing spring and an SMA spring. Upon actuation of the SMA spring at a phase transition temperature, the sleeve is configured to shift and expose flow ports formed in the body.

Systems and methods for measuring a parameter of interest in a borehole in an earth formation are provided. The systems include a downhole sensor having a first sensor component with a first temperature and a second sensor component with a second temperature, the downhole sensor disposed on a downhole component. A temperature control system is configured with a thermal control mechanism operatively connected to at least one of the first and second sensor components. The thermal control mechanism is configured to maintain a temperature difference between the first temperature and the second temperature below a pre-determined temperature difference. The downhole sensor is configured to measure the parameter of interest when the temperature difference is below the pre-determined temperature difference.

A downhole tool, for removing sections of metal tubing, said downhole tool comprising at least one conductive element being arranged to corrode a section of metal tubing using an electrolytic process, said conductive element being made of electric conductive material, an apparatus to establish a connection to the metal tubing, and a source of electrical power.

Systems and methods for cooling an electronics compartment of a downhole tool include a tool assembly. The tool assembly is an elongated member formed of axially aligned tool units. The tool units include a turbine and the electronics compartment. The electronics compartment has an interior cavity containing electronics components. The tool units further include a compressor powered by the turbine. The compressor is operable to compress a coolant fluid. The compressor has a central heat exchanger operable to cool a non-electrically conductive fluid with the coolant fluid. An impeller is rotated by the turbine. The impeller is operable to circulate the non-electrically conductive fluid past the electronics components.

Systems and methods for cooling an electronics compartment of a downhole tool include a tool assembly. The tool assembly is an elongated member formed of axially aligned tool units. The tool units include a turbine and the electronics compartment. The electronics compartment has an interior cavity containing electronics components. The tool units further include a compressor powered by the turbine. The compressor is operable to compress a coolant fluid. The compressor has a central heat exchanger operable to cool a non-electrically conductive fluid with the coolant fluid. An impeller is rotated by the turbine. The impeller is operable to circulate the non-electrically conductive fluid past the electronics components.