CROSS-REFERENCE TO RELATED APPLICATIONS
- STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
The present invention relates generally to methods and apparatus for operating electronic components on a downhole tool within a wellbore. More particularly, the present invention relates to methods and apparatus for controlling the temperature of downhole electronic components.
Many wellbore logging and evaluation tools utilize electronic components to gather data from the wellbore and surrounding formation and transmit that data back to the surface. Because the temperature within a wellbore increases with depth, these electronic components are routinely exposed to very high ambient temperatures. The temperature of the electronic components is also increased by the consumption and production of power by the electronic components themselves.
Many of these electronic components may be temperature sensitive components that may face degrading performance with increasing temperatures. Further, some of the electronic components may only satisfactorily operate within a certain range of temperatures. Therefore, as the complexity and sophistication of the electronic components disposed within downhole tools increases, methods and apparatus for cooling these components take on greater importance.
Several downhole electronic component cooling systems have been developed that use an array of temperature control technologies. Some of these systems are passive systems that seek to insulate the electronic components to delay the inevitable temperature increase. These passive systems extend the operating life of the tool but may or may not provide sufficient operating life to accomplish the desired analysis.
Active systems are also available that cool the electronic components through refrigeration or some other temperature control technique. Active systems require a source of power, such as a supply of chilled fluid from the surface or electricity from a battery or turbine located downhole. The sources of power are often limited and the power consumed by the cooling system reduces the power available to the electronic components to perform the desired monitoring.
- SUMMARY OF THE PREFERRED EMBODIMENTS
There remains a need to develop more efficient methods and apparatus for controlling the temperature of downhole electronic components that overcome some of the foregoing difficulties while providing more advantageous overall results.
The problems noted above are solved in a large part by apparatus and methods for operating an electronics assembly of a downhole tool. A method comprises disposing a temperature-sensitive electronic component within an insulated chamber contained within a downhole tool. The temperature of the temperature-sensitive electronic component is monitored and a temperature control system is selectively activated to regulate the temperature of the temperature-sensitive electronic component. A downhole electronic assembly comprises a temperature-sensitive electronic component and a temperature-tolerant electronic component in electrical communication with the temperature-sensitive electronic component. An insulating chamber provides a thermal barrier between the temperature-sensitive electronic component and the temperature-tolerant electronic component. A temperature control apparatus in thermal communication with the temperature-sensitive component.
BRIEF DESCRIPTION OF THE DRAWINGS
Thus, the present invention comprises a combination of features and advantages that enable it to overcome various problems of prior devices. The various characteristics described above, as well as other features, will be readily apparent to those skilled in the art upon reading the following detailed description of the preferred embodiments of the invention, and by referring to the accompanying drawings.
For a more detailed description of the preferred embodiment of the present invention, reference will now be made to the accompanying drawings, wherein:
FIG. 1 is an illustration of a drilling rig including a measurement while drilling tool;
FIG. 2 is a schematic illustration of an electronic assembly of a downhole tool; and
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 3 is a schematic illustration of a cooling system constructed in accordance with embodiments of the invention.
Referring now to FIG. 1, a drilling rig 10 supports and drives a drill string 12 to form a wellbore 14. Located at the distal end of drill string 12 is a bottom hole assembly 16 comprising drill bit 18 and monitoring tool 20. Monitoring tool 20 includes power supply 22 and electronics module 24. Electronics module 24 includes data acquisition module 26 and data storage and transfer module 28. Acquisition module 26 gathers data, such as seismic data or pressure data, from wellbore 14 and/or the surrounding formation. This data is stored in storage and transfer module 28 and communicated to surface module 30, via cable connections, sonic signals, or wireless telemetry.
Referring now to FIG. 2, electronics assembly 200 is shown including power supply 202, temperature-tolerant electronic component 204, temperature-sensitive electronic component 206, and temperature control system 208. Temperature-sensitive electronic component 206 is isolated within insulated chamber 210. Temperature control system 208 includes temperature sensor 212, temperature regulator 214, and controller 216. Sensor 212 and regulator 214 are partially disposed within, or in thermal communication with, insulated chamber 210. Controller 216 may be located outside of chamber 210.
Temperature-tolerant component 204 includes those electronics that have operating envelopes including relatively high temperatures and those components that tend to generate large amounts of heat during operation. Temperature-sensitive component 206 includes one or more components that have operating characteristics significantly dependent on temperature. This temperature dependence may be manifested in a variety of ways, including a degradation of performance, an inability to fully function, and a limitation on stability.
In operation, controller 216 monitors the temperature inside chamber 210 via sensor 212. Controller 216 operates regulator 214 that adds or removes heat from chamber 210 in order to maintain a desired temperature for temperature-sensitive component 206. Once the temperature within chamber 210 reaches a desired level, controller 216 shuts down regulator 214. Regulator 214 may be periodically activated to keep the temperature within chamber 210 within a desired range. By isolating temperature-sensitive component 206 within chamber 210, the mass of the temperature controlled components and the required heating load can be reduced.
Assembly 200 may include one or more chambers 210 isolating separate temperature-sensitive components 206. Each separate chamber 210 may have its own temperature control system 208 such that each temperature-sensitive component 206 can be maintained within a selected temperature range independent of the temperature ranges for the other components.
Referring now to FIG. 3, temperature control assembly 300 is shown including temperature-sensitive component 302, thermoelectric cooler 304, heat sink 306, insulated chamber 308, temperature sensor 310, thermostat 312, and amplifier 313. Temperature-sensitive component 302 is disposed within insulated chamber 308 and in thermal contact with thermoelectric cooler 304. Heat sink 306 is located outside of insulated chamber 308 and in thermal contact with thermoelectric cooler 304. Thermostat 312 monitors the temperature within chamber 308 via sensor 310 and provides power to thermoelectric cooler 304 through amplifier 313 and electrical connection 314. Amplifier 313 may be a class-D amplifier, liner amplifier, variable switch-mode power supply, or a switching amplifier.
Thermoelectric cooler 304 is a Peltier-type device comprising p-type semiconductor 316 and n-type semiconductor 318 sandwiched between two conductive plates 320, 322. Semiconductors 316, 318 are connected electrically in series and thermally in parallel. Conductive plates 320, 322 have a high thermal conductivity and are often a ceramic material, such as a metallized beryllium oxide and/or an aluminum oxide. In certain embodiments, conductive plate 320 may be integrated into component 302. A DC voltage is applied through electrical connection 314.
A positive DC voltage applied to n-type semiconductor 318 causes electrons to pass from p-type semiconductor 316 to n-type semiconductor 318. As these electrons pass to n-type semiconductor 318 they absorb heat, essentially causing heat to flow from conductive plate 320 to conductive plate 322. This, in effect, acts as a heat pump, transferring heat from temperature-sensitive component 302 to heat sink 306.
A negative DC voltage applied to n-type semiconductor 318 has the reverse effect and causes electrons to pass from n-type semiconductor 318 to p-type semiconductor 316. As these electrons pass to p-type semiconductor 316 they absorb heat, essentially causing heat to flow from conductive plate 322 to conductive plate 320. This, in effect, acts as a heat pump, transferring heat to temperature-sensitive component 302 from heat sink 306.
Semiconductors 316, 318 may be fabricated from an alloy of bismuth, telluride, selenium, and antimony and may be doped and processed to yield polycrystalline semiconductors with anisotropic thermoelectric properties. A plurality of thermoelectric coolers 304 may be stacked in a multistage or cascading arrangement to increase the potential thermal transfer through the cooler.
Temperature control assembly 300 can be operated in a first mode where thermostat 312 is utilized to maintain the temperature within chamber 308 within a selected temperature range. For example, temperature-sensitive component 302 may be a temperature compensated zener diode being used as a voltage reference in a downhole application. Further, the zener diode may be specifically constructed to have a zero temperature coefficient (ZTC) at or near 150° C., normally the ZTC point is engineered to occurs at approximately 25° C. or ambient room temperature.
Thermostat 312 is used to control the environment of the zener diode and other temperature sensitive components within chamber 308. Thermostat 312 senses the temperature within chamber 308 via sensor 310 and operates thermoelectric cooler 304 to maintain the temperature at 150° C.+/−2° C. As operation of the downhole tool is initiated, the temperature within chamber 308 can be increased to within the desired range by operating thermoelectric cooler 304 as a heater. Once the tool is downhole and subjected to higher ambient temperatures, the thermoelectric cooler 304 can be operated as a cooler to maintain the temperature within the desired range.
Operation in this mode allows the temperature sensitive components to operate at a relatively constant temperature and effectively shifts much of the burden of stabilization to the accuracy of the thermostat and thus away from having to perform higher order curvature corrections. Regulating the temperature of the selected components provides an efficient and cost effective way of stabilizing the output voltages of the zener diode voltage reference without any high order curvature correction schemes.
Temperature control assembly 300 can also be operated in a second mode where thermostat 312 is utilized to intermittently maintain the temperature within chamber 308 within a selected temperature range. For example, temperature-sensitive component 302 may be a memory storage component in a downhole application. Many memory components can effectively store data at higher temperatures than are allowable for reading and writing to the memory.
Thermostat 312 can be used to control the environment of the memory components within chamber 308. Thermostat 312 senses the temperature within chamber 308 via sensor 310. When data is ready to be written to, or read from, the memory thermoelectric cooler 304 is operated to reduce the temperature to within the allowable range. Once the read/write process is complete, thermoelectric cooler 304 is deactivated and the temperature within chamber 308 is allowed to increase.
Batch cooling the memory modules in this manner allows for more efficient use of power from a limited supply of power often associated with a downhole application. This batch cooling method could also be used with a voltage reference to cool the reference only when being used or with a calibration reference that benefits from being calibrated to a controlled temperature. Batch cooling methods could also be used with other temperature control and refrigeration systems and are not limited to use with thermoelectric coolers.
While preferred embodiments of this invention have been shown and described, modifications thereof can be made by one skilled in the art without departing from the scope or teaching of this invention. The embodiments described herein are exemplary only and are not limiting. Many variations and modifications of the system and apparatus are possible and are within the scope of the invention. For example, the relative dimensions of various parts, the materials from which the various parts are made, and other parameters can be varied, so long as the apparatus retain the advantages discussed herein. Accordingly, the scope of protection is not limited to the embodiments described herein, but is only limited by the claims that follow, the scope of which shall include all equivalents of the subject matter of the claims.