Abstract:
A cooling system in which an electronic device or other component is cooled by using one or more solid sources of liquid vapor (such as polymeric absorbents, hydrates or desiccants that desorb water at comparatively low temperature) in conjunction with one or more high-temperature vapor sorbents or desiccants that effectively transfer heat from the component to the fluid in the wellbore. Depending on the wellbore temperature, desiccants are provided that release water at various high regeneration temperatures such as molecular sieve (220-250° C.), potassium carbonate (300° C.), magnesium oxide (800° C.) And calcium oxide (1000° C.). A solid water source is provided using a water-absorbent polymer, such as sodium polyacrylate. Heat transfer is controlled in part by a check valve selected to release water vapor at a selected vapor pressure.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This patent application is a continuation and claims priority from U.S. patent application Ser. No. 10/847,243 filed on May 17, 2004 entitled “Downhole Sorption Cooling and Heating in Wire line Logging and Monitoring While Drilling” by Rococo DiFoggio et al, which is incorporated herein by reference in its entirety, now U.S. Pat. No. 7,124,596 which is a continuation-in-part of and claims priority from U.S. patent application Ser. No. 10/232,446 filed on Aug. 30, 2002, now U.S. Pat. No. 6,877,332 entitled “Downhole Sorption Cooling of Electronics in Wire line Logging and Monitoring While Drilling” by Rococo DiFoggio, which is also a continuation-in-part of and claims priority from U.S. patent application Ser. No. 10/036,972 filed on Dec. 21, 2001, now U.S. Pat. No. 6,672,093 entitled “Downhole Sorption Cooling of Electronics in Wire line Logging and Monitoring While Drilling” by Rococo DiFoggio, which is also a continuation-in-part of and claims priority from U.S. patent application Ser. No. 09/756,574 filed on Jan. 8, 2001, now U.S. Pat. No. 6,341,498 entitled “Downhole Sorption Cooling of Electronics in Wire line Logging and Monitoring While Drilling” by Rococo DiFoggio. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This present invention relates to a downhole tool for wireline or monitoring while drilling applications, and in particular relates to a method and apparatus for sorption cooling of sensors and electronics and heating of chambered samples deployed in a downhole tool suspended from a wireline or a drill string. 
   2. Summary of Related Art 
   In underground drilling applications, such as oil and gas or geothermal drilling, a bore hole is drilled through a formation deep in the earth. Such bore holes are drilled or formed by a drill bit connected to the end of a series of sections of drill pipe, so as to form an assembly commonly referred to as a “drill string.” The drill string extends from the surface to the bottom of the bore hole. As the drill bit rotates, it advances into the earth, thereby forming the bore hole. In order to lubricate the drill bit and flush cuttings from its path as it advances, a high pressure fluid, referred to as “drilling mud,” is directed through an internal passage in the drill string and out through the drill bit. The drilling mud then flows to the surface through an annular passage formed between the exterior of the drill string and the surface of the bore. 
   The distal or bottom end of the drill string, which includes the drill bit, is referred to as a “downhole assembly.” In addition to the drill bit, the downhole assembly often includes specialized modules or tools within the drill string that make up the electrical system for the drill string. Such modules often include sensing modules. In many applications, the sensing modules provide the drill string operator with information regarding the formation as it is being drilled through, using techniques commonly referred to as “measurement while drilling” (MWD) or “logging while drilling” (LWD). For example, resistivity sensors may be used to transmit and receive high frequency signals (e.g., electromagnetic waves) that travel through the formation surrounding the sensor. 
   As can be readily appreciated, such an electrical system will include many sophisticated electronic components, such as the sensors themselves, which in many cases include printed circuit boards. Additional associated components for storing and processing data in the control module may also be included on printed circuit boards. Unfortunately, many of these electronic components generate heat. For example, the components of a typical MWD system (i.e., a magnetometer, accelerometer, solenoid driver, microprocessor, power supply and gamma scintillator) may generate over 20 watts of heat. Moreover, even if the electronic component itself does not generate heat, the temperature of the formation itself typically exceeds the maximum temperature capability of the components. 
   Overheating frequently results in failure or reduced life expectancy for thermally exposed electronic components. For example, photo multiplier tubes, which are used in gamma scintillators and nuclear detectors for converting light energy from a scintillating crystal into electrical current, cannot operate above 175° C. Consequently, cooling of the electronic components is important. Unfortunately, cooling is made difficult by the fact that the temperature of the formation surrounding deep wells, especially geothermal wells, is typically relatively high, and may exceed 200° C. 
   Certain methods have been proposed for cooling electronic components in applications associated with the monitoring and logging of existing wells, as distinguished from the drilling of new wells. One such approach, which requires isolating the electronic components from the formation by incorporating them within a vacuum insulated Dewar flask, is shown in U.S. Pat. No. 4,375,157 (Boesen). The Boesen device includes thermoelectric coolers that are powered from the surface. The thermoelectric coolers transfer heat from the electronics area within the Dewar flask to the well fluid by means of a vapor phase heat transfer pipe. Such approaches are not suitable for use in drill strings since the size of such configurations makes them difficult to package into a downhole assembly. 
   Another approach, as disclosed in U.S. Pat. No. (Owens) involves placing a thermoelectric cooler adjacent to an electronic component or sensor located in a recess formed in the outer surface of a well logging tool. This approach, however, does not ensure that there will be adequate contact between the components to ensure efficient heat transfer, nor is the electronic component protected from the shock and vibration that it would experience in a drilling application. 
   Thus, one of the prominent design problems encountered in downhole logging tools is associated with overcoming the extreme temperatures encountered in the downhole environment. Thus, there exists a need to reduce the temperature within the downhole tool in the region containing the electronics, to the within the safe operating level of the electronics. Various schemes have been attempted to resolve the temperature differential problem to keep the tool temperature below the maximum electronic operating temperature, but none of the known techniques have proven satisfactory. 
   Downhole tools are exposed to tremendous thermal strain. The downhole tool housing is in direct thermal contact with the bore hole drilling fluids and conducts heat from the bore hole drilling fluid into the downhole tool housing. Conduction of heat into the tool housing raises the ambient temperature inside of the electronics chamber. Thus, the thermal load on a non-insulated downhole tool&#39;s electronic system is enormous and can lead to electronic failure. Electronic failure is time consuming and expensive. In the event of electronic failure, downhole operations must be interrupted while the downhole tool is removed from deployment and repaired. Thus, various methods have been employed in an attempt to reduce the thermal load on all the components, including the electronics and sensors inside of the downhole tool. To reduce the thermal load, downhole tool designers have tried surrounding electronics with thermal insulators or placed the electronics in a vacuum flask. Such attempts at thermal load reduction, while partially successful, have proven problematic in part because of heat conducted from outside the electronics chamber and into the electronics flask via the feed-through wires connected to the electronics. Moreover, heat generated by the electronics trapped inside of the flask also raises the ambient operating temperature. 
   Typically, the electronic insulator flasks have utilized high thermal capacity materials to insulate the electronics to retard heat transfer from the bore hole into the downhole tool and into the electronics chamber. Designers place insulators adjacent to the electronics to retard the increase in temperature caused by heat entering the flask and heat generated within the flask by the electronics. The design goal is to keep the ambient temperature inside of the electronics chamber flask below the critical temperature at which electronic failure may occur. Designers seek to keep the temperature below critical for the duration of the logging run, which is usually less than 12 hours. 
   Electronic container flasks, unfortunately, take as long to cool down as they take to heat up. Thus, once the internal flask temperature exceeds the critical temperature for the electronics, it requires many hours to cool down before an electronics flask can be used again safely. Thus, there is a need to provide an electronics and or component cooling system that actually removes heat from the flask or electronics/sensor region without requiring extremely long cool down cycles which impede downhole operations. As discussed above, electronic cooling via thermoelectric and compressor cooling systems has been considered, however, neither have proven to be viable solutions. 
   Thermoelectric coolers require too much external power for the small amount of cooling capacity that they provide. Moreover, few if any of the thermoelectric coolers are capable of operating at downhole temperatures. Additionally, as soon as the thermoelectric cooler system is turned off, the system becomes a heat conductor that enables heat to rapidly conduct through the thermoelectric system and flow back into the electronics chamber from the hotter regions of the downhole tool. Compressor-based cooling systems also require considerable power for the limited amount of cooling capacity they provide. Also, most compressors seals cannot operate at the high temperatures experienced downhole because they are prone to fail under the thermal strain. 
   Thus, there is a need for a cooling system that addresses the problems encountered in known systems discussed above. Consequently, it would be desirable to provide a rugged yet reliable system for effectively cooling the electronic components and sensors utilized downhole that is suitable for use in a wellbore. It is desirable to provide a cooling system that is capable of being used in a downhole assembly of a drill string or wireline. 
   Another problem encountered during downhole operations is cooling and associated depressurization of hydrocarbon samples taken into a downhole tool. As the tool is retrieved from the bore hole the sample cools and depressurizes. Thus there is a need for heating method and apparatus to prevent cooling and depressurization of downhole hydrocarbon samples. 
   SUMMARY OF THE INVENTION 
   It is an object of the current invention to provide a rugged yet reliable system for effectively cooling the electronic components that is suitable for use in a well, and preferably, that is capable of being used in a downhole assembly of a drill string or wire line. This and other objects is accomplished in a sorption cooling system in which an electronic component or sensor is juxtaposed with one or more sorbent coolers that facilitate the transfer of heat from the component to the wellbore. Depending on the wellbore temperature, desiccants that release water at various high regeneration temperatures are used such as molecular sieve (220-250° C.), potassium carbonate (300° C.), magnesium oxide (800° C.) And calcium oxide (1000° C.). A solid source of water is provided using a water-absorbent polymer, such as sodium polyacrylate or a low-regeneration-temperature desiccant. Heat transfer is controlled in part by a check valve selected to release water vapor at a selected vapor pressure. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For detailed understanding of the present invention, references should be made to the following detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings, in which like elements have been given like numerals, wherein: 
       FIG. 1  is an illustration of a preferred embodiment of the present invention shown in a monitoring while drilling environment; 
       FIG. 2  is a longitudinal cross section through a portion of the down tool attached to the drill string as shown in  FIG. 1  incorporating the sorbent cooling apparatus of the present invention; 
       FIG. 3  is a schematic representation of an example of the present invention in operation down hole; 
       FIG. 4  is an illustration an exemplary embodiment of the present invention showing a highly heat-conductive polymer proximate to the circuit board for removing heat from the circuit board; 
       FIG. 5  is an illustration of a list of examples of desiccants having differing temperature ranges at which they release water; and 
       FIG. 6  illustrates that the temperature dependence of vapor pressure is approximately the same for liquid water as it is for water absorbed in a solid sodium polyacrylate matrix. A check valve based on this vapor pressure curve can be used to provide temperature regulation. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The present invention provides a structure and method for a downhole tool component cooling system. The downhole tool component cooling system of the present invention does not require an external electrical power source. The cooling system of the present invention utilizes the potential energy of sorption to remove heat from a temperature sensitive tool component. The sorption energy removes heat from the tool component and moves the heat to a second, hotter region in the downhole tool. The cooling region of the tool, adjacent to the temperature-sensitive component which is sorption cooled, contains a liquid source (such as water) which in the present example is a solid form of water to avoid spillage. The solid source of water releases its water as its temperature increases. Thus, this solid source of water can be a low-temperature hydrate, desiccant, sorbent, or polymeric absorber from which water (or some other liquid) vapor is generated when heated sufficiently. For example, sodium polyacrylate is a polymeric water absorber that can absorb up to 40 times its weight in water and still appear to be a dry solid. 
   Cooling occurs as a first portion of the solid source of water releases water vapor. Upon release from the first portion of the solid source of water, the remaining portion of this solid source of water is cooled, and this remaining portion in turn cools the adjacent thermally sensitive component, thereby keeping the adjacent component within a safe operating temperature with continued sorption cooling. Thus, the present invention provides a structure and method whereby the downhole electronics or other thermally-sensitive components are surrounded by or adjacent to a solid source of water, such as a low-temperature hydrate, desiccant, sorbent, polymeric absorber or some mixture of these. The solid source of water surrounding or adjacent to the electronics or thermally sensitive component is cooled by release of the water vapor (or other liquid vapor), thereby cooling the electronics or other thermally-sensitive component, e.g., a sensor. 
   According to the present example of the invention, a sorbent cooling system for use in a well, such as downhole tool in a drill string through which a drilling fluid flows, or a wire line comprises (i) a housing adapted to be disposed in a well and exposed to the fluid in the well, (ii) a solid source of liquid (e.g., a low-regeneration-temperature hydrate, desiccant, sorbent, or polymeric absorber that releases water when heated), adjacent to a thermally sensor or electronic component to be cooled, (iii) optionally, a Dewar flask lined with phase change material surrounding the electronics/sensor and liquid supply, (iv) optionally, a vapor passage for transferring vapor from the liquid supply; and (v) a high-temperature sorbent or desiccant in thermal contact with the housing for receiving and adsorbing the water vapor from the vapor passage and transferring the heat from the water vapor through the housing to the drilling fluid or wellbore. A desiccant is a specific type of sorbent, that is a substance that sorbs (adsorbs or absorbs) water. All desiccants are soreness but not all soreness are desiccants. The electronics or sensor adjacent to the low-temperature hydrate, desiccant, or sorbent is kept cool by the latent heat of fusion and heat of desorption. 
   A drilling operation according to the current invention is shown in  FIG. 1 . A drill rig  1  drives a drill string  3  that, which typically is comprised of a number of interconnecting sections. A downhole assembly  11  is formed at the distal end of the drill string  3 . The downhole assembly  11  includes a drill bit  7  that advances to form a bore  4  in the surrounding formation  6 . A portion of the downhole assembly  11 , incorporating an electronic system  8  and cooling systems according to the current invention, is shown in  FIG. 2 . The electrical system  8  may, for example, provide information to a data acquisition and analysis system  13  located at the surface. The electrical system  8  includes one or more electronic components. Such electronic components include those that incorporate transistors, integrated circuits, resistors, capacitors, and inductors, as well as electronic components such as sensing elements, including accelerometers, magnetometers, photomultiplier tubes, and strain gages. 
   The downhole portion  11  of the drill string  3  includes a drill pipe, or collar,  2  that extends through the bore  4 . As is conventional, a centrally disposed passage  20  is formed within the drill pipe  2  and allows drilling mud  22  to be pumped from the surface down to the drill bit. After exiting the drill bit, the drilling mud  23  flows up through the annular passage formed between the outer surface of the drill pipe  2  and the internal diameter of the bore  4  for return to the surface. Thus, the drilling mud flows over both the inside and outside surfaces of the drill pipe. Depending on the drilling operation, the pressure of the drilling mud  22  flowing through the drill pipe internal passage  20  will typically be between 1,000 and 20,000 pounds per square inch, and, during drilling, its flow rate and velocity will typically be in the 100 to 1500 GPM range and 5 to 150 feet per second range, respectively. 
   As also shown in  FIG. 2 , the electrical system  8  is disposed within the drill pipe central passage  20 . The electrical system  8  includes a number of sensor modules  10 , a control module  12 , a power regulator module  14 , an acoustic pulser module  18 , and a turbine alternator  16  that are supported within the passage  20 , for example, by struts extending between the modules and the drill pipe  2 . According to the current invention, power for the electrical system  8 , including the electronic components and sensors, discussed below, is supplied by a battery, a wireline or any other typical power supply method such as the turbine alternator  16 , shown in  FIG. 2 , which is driven by the drilling mud  22 . The turbine alternator  16  may be of the axial, radial or mixed flow type. Alternatively, the alternator  16  could be driven by a positive displacement motor driven by the drilling mud  22 , such as a Moineau-type motor. In other embodiments, power could be supplied by any power supply apparatus including an energy storage device located downhole, such as a battery. 
   As shown in  FIG. 3 , each sensor module  10  is comprised of a cylindrical housing  52 , which is preferably formed from stainless steel or a beryllium copper alloy. An annular passage  30  is formed between the outer surface  51  of the housing  52  and the inner surface of the drill pipe  2 . The drilling mud  22  flows through the annular passage  30  on its way to the drill bit  7 , as previously discussed. The housing  52  contains an electronic component  54  for the sensor module. The electronic component  54  may, but according to the invention does not necessarily, include one or more printed circuit boards including a processor associated with the sensing device, as previously discussed. Alternatively, the assembly shown in  FIG. 3  comprises the control module  12 , power regulator module  14 , or pulser module  18 , in which case the electronic component  54  may be different than those used in the sensor modules  10 , although it may, but again does not necessarily, include one or more printed circuit boards. According to the current invention, one or more of the electronic components or sensors in the electrical system  8  are cooled by evaporation of liquid from the liquid supply  132  adjacent to or surrounding electronics  54 . In an alternative embodiment as shown in  FIG. 3 , the electrical system, for example a clock which remains at a constant temperature, is cooled by the evaporation of a liquid provided by a low-temperature hydrate or desiccant  232  adjacent the electronics, e.g., an electronic clock. 
   A highly heat-conductive polymer is optionally provided proximate or touching the electronics or circuit board to facilitate heat removal from the electronics or circuit board, as shown in  FIG. 4 . These polymers are typically loaded with highly heat-conductive minerals. At room temperature, they feel quite cool to the touch because they quickly draw heat from one&#39;s fingers. Water is a particularly effective coolant. Evaporation of one liter of water removes 631.63 Watt-hours of energy, which equals 543 cal/ml. Water is also inexpensive, readily available worldwide, nontoxic, chemically stable, and poses no environmental disposal problems. Thus, evaporation of one liter of water can remove 632 Watts for one hour, 63 Watts for 10 hours, or 6.3 Watts for 100 hours. In the present example of the present invention, a low-temperature solid source of water is placed inside the cooling region of the downhole tool, preferably inside a Dewar flask. A high-temperature desiccant that is in thermal contact with the wellbore fluid adsorbs the water released by the low-temperature solid source of water. The high-temperature desiccant is chosen based on the desired operating temperature, that is, the temperature at which a desiccant releases water. 
   A partial list of suitable desiccants is shown in  FIG. 5  with each desiccant&#39;s associated water release temperature, that is, the regeneration temperature for the desiccant. There are numerous other desiccants suitable which are not listed in  FIG. 5 . The list of  FIG. 5  is not meant to be exhaustive, as other desiccants are suitable as well for use in the present invention. The Dewar flask or container, comprising a cooling chamber, is connected via a vapor passage, such as a tube, to a container of high-temperature desiccant located in a higher temperature heat sink region located elsewhere in the tool. The preferred high-temperature desiccant strongly sorbs water vapor, which has traveled from the evaporation (cooling) region through the vapor passage to the high-temperature desiccant in the heat sink region. The heat sink region, containing the desiccant is in efficient thermal contact with the downhole tool housing which is in thermal contact with the high temperature wellbore. The higher temperature desiccant sorbs the water vapor from the vapor passage at elevated temperatures, thereby keeping the vapor pressure low. Low vapor pressure facilitates additional water vapor release from the lower temperature water source, enabling additional cooling within the cooling chamber containing the evacuated electronics Dewar flask or other container surrounding or adjacent to the electronics in the cooling chamber. 
   In an exemplary embodiment, approximately 6.25 volumes of loosely packed high-temperature desiccant are utilized to sorb 1 volume of water. After each logging run, the high-temperature desiccant can either be discarded or regenerated. This higher temperature desiccant can be regenerated by heating it to the water release temperature to release the water or other liquid it has absorbed by the higher temperature desiccant during sorption cooling. Some soreness, referred to as desiccants, are able to selectively sorb water. Some desiccants retain sorbed water even at relatively high temperatures. Molecular Sieve 3A (MS-3A), and 13X are synthetic zeolites that are high-temperature desiccants. The temperature for desiccant regeneration, or expulsion of sorbed water for MS-3A ranges from 175° to 350° centigrade. As shown in  FIG. 5 , numerous other desiccants with a variety of regeneration temperatures are available, depending upon the selection of a particular desiccant having a particular regeneration temperature. The desiccant regeneration temperature is selected to exceed temperatures encountered during operation tool operations while sorption cooling is desired to enable a continuous intake of water vapor by the higher temperature desiccant. For example, calcium oxide (CaO) chemisorbs water and retains that water to 1000 C. Once the regeneration temperature is reached, water vapor is no longer sorbed by the higher temperature desiccant, rather the water vapor that has already been taken in by the higher temperature desiccant is released. 
   Turning now to  FIGS. 4A and 4B , an exemplary embodiment of the present invention is depicted.  FIG. 4A  is a side view of a schematic representation of the present invention showing a Dewar flask/pressure housing  1210  surrounding a low temperature water source desiccant  1226 , which can be any suitable desiccant selected for a desired operating temperature range. The low temperature solid source of water  1226  is placed adjacent an item to be cooled, such as a printed circuit board, processor or electronics  1212 . In the present example, a compliant thermal pad  1224  having very high heat conductivity is optionally placed in contact with the circuit board and integrated circuits on the circuit board. It prevents hot spots from developing on the boards. The pad  1224  also facilitates conduction of heat from the circuit board  1212  to the desiccant  1226  for cooling of the circuit board. At a pre-selected vapor pressure, a check valve  1214 , opens. It was chosen in accordance with  FIG. 6  to maintain a relatively constant temperature in the electronics  1212  being cooled. That is, it maintains that temperature, which corresponds to the vapor pressure at which it opens. When the check valve opens at a desired vapor pressure, it allows vapor from solid source of water  1226  to flow through high pressure polyamide tubing  1217  and  1216  and on to high-temperature desiccant  1230 . The check valve  1214  controls the rate of evaporation of water from solid source of water  1226  and the flux of vapor to the high-temperature sorbent  1230  by opening at a preselected vapor pressure to allow evaporation. The check valve  1214  closes when the vapor pressure associated with the solid source of water  1226  drops below the designed vapor pressure.  FIG. 4B  is a cross section taken along section line B-B of  FIG. 4A . A thermally conductive coupler such as a wire mesh  1213  is distributed throughout the low temperature solid source of water  1226  water source to ensure equal evaporation of water vapor from the low temperature desiccant. Some additional thermal insulation  1218  is provided. To minimize heat transfer to the circuit board  1212  from the connector  1220  through the cable  1222 , this cable is coiled to increase its length. 
   Turning now to  FIGS. 5A ,  5 B and  5 C, a list of suitable desiccants  1310  is given illustrating a subset of desiccants are shown along with their regeneration temperature  1320 . Some of the desiccants are not recommended, as noted, because of the toxicity associated there with. 
     FIG. 6  is graph of the vapor pressure versus temperature for selection of check valve  1214  for maintaining a relatively constant temperature for the electronics  1212 . A vacuum is pulled on each side of the check valve to facilitate water evaporation from the solid source of water and to facilitate its transfer to the high temperature desiccant. 
   While the foregoing disclosure is directed to the preferred embodiments of the invention various modifications will be apparent to those skilled in the art. It is intended that all variations within the scope and spirit of the appended claims be embraced by the foregoing disclosure. Examples of the more important features of the invention have been summarized rather broadly in order that the detailed description thereof that follows may be better understood, and in order that the contributions to the art may be appreciated. There are, of course, additional features of the invention that will be described hereinafter and which will form the subject of the claims appended hereto.