Cooling of sensors and electronics used for down hole oil and geothermal wells is critical to the operation of these systems in MWD (measurement while drilling) applications. The temperatures and pressures imposed on the down-hole assembly, increase with well depth and are generally higher than the survival temperatures of these sensors and electronics without cooling. Many approaches to cool or protect the sensing and electrical systems have been proposed and implemented over the years including vacuum Dewar flasks and thermoelectric refrigerators, sorption coolers, heat exchangers, cryogenic cells, Sterling coolers and vortex coolers. Almost all of these methods rely on the drilling mud that is pumped through the drill string to provide the final medium to carry away heat from the down-hole assembly.
Maintaining optimal payload temperatures in a typical down hole environment of 230˚C requires that the MWD cooling system be capable of pumping a significant load and requires a low thermal resistance path on the heat rejection (hot) side of the TEC. The application environment of high temperature, high pressure, mechanical shock and vibration require the use of high temperature thermoelectric materials and assemblies that are capable of withstanding the mechanical environment.
New Cooling Approaches
Cooling of electronic components inside a MWD housing can be accomplished using thin-film thermoelectric cooling devices with one or both of the following two strategies: local cooling of individual components or with a refrigeration unit that cools the ambient environment inside the insulated MWD housing.
Cooling on a component-by-component level can be accomplished by placing the TEC between the electronic package and a heat spreader or sink. This “distributed” arrangement of TECs throughout the flask increases the temperature of the ambient inside the housing while cooling the electronic component directly. The effectiveness of this approach depends on the thermal resistance of and the amount of heat generated by the component package.
In the second approach (centralized cooling) TECs effectively refrigerate the ambient inside the MWD housing. The TEC must handle the entire heat load of all the electronic components as well as any heat absorbed through the walls of the housing. The effectiveness of this approach depends on the degree that heat from the electronic components can be transferred to the cold side of the TEC.
Nextreme Products for Down Hole Refrigeration
UPF40 - ideal for applications with high heat-flux requirements. More >
HV14 - a high voltage, low current thermoelectric cooler designed for standard electrical power requirements. More >
Custom Modules - provides the customer with a device optimized for thermal management, efficiency and form factor. More >