Open loop cooling system and method for downhole tools

A downhole tool (100) including an open loop cooling system (110) having a pressurized container (120) disposed within a tool string, and has a refrigerant (122). The cooling system further includes a tank (150) in fluid communication with the pressurized container (120), and a heat exchanger (160) associated with tank (150), where the heat exchanger exchanges heat between the refrigerant (122) and a downhole payload (164). The cooling system further includes a low pressure apparatus that creates a low pressure region proximate the pressurized container. The low pressure apparatus can include a venturi (180). The venturi has a drilling mud passage (188) therethrough, and drilling mud flowing through a convergence (186) creates a low pressure adjacent the tank (150).

RELATED APPLICATIONS

This application is a U.S. National Stage Filing under 35 U.S.C. 371 from International Application No. PCT/US2009/063278, filed on Nov. 4, 2009, and published as WO 2011/056171 A1 on May 2, 2011; which application and publication are incorporated herein by reference in their entirety.

TECHNICAL FIELD

The application relates generally to downhole drilling. In particular, the application relates to a cooling system used during the work with a downhole tool.

BACKGROUND

In order to obtain measurements and information from the downhole environment while drilling, the tool includes electronic devices. Downhole tools must be able to operate near the surface of the earth as well as many thousands of feet below the surface. Environmental temperatures tend to increase with depth during the drilling of the well. As the depth increases, the tools are subjected to a severe operating environment. For instance, downhole temperatures are generally high and may even exceed 200 degrees C. In addition, pressures may exceed 20,000 psi. In addition to the high temperature and pressure, there is also vibration and shock stress associated with operating in the downhole environment, particularly during drilling operations.

The electronic components in the downhole tools also internally generate heat. For example, a typical wireline tool may dissipate over 100 watts of power, and a typical downhole tool on a drill string may dissipate over 10 watts of power. Although there is electrical power dissipated by a drill string tool, the heat from the drilling environment itself still makes internal heat dissipation a problem. The internally dissipated heat must be removed from the electronic components or thermal failure will occur.

DETAILED DESCRIPTION

Methods, apparatus and systems for cooling components of a downhole tool using an open loop system are described. The open loop cooling system includes a refrigerant stored in a container which is continually consumed over the span of cooling time needed. In the following description, numerous specific details are set forth. However, it is understood that embodiments of the invention may be practiced without these specific details. In other instances, well-known circuits, structures and techniques have not been shown in detail in order not to obscure the understanding of this description. Some embodiments may be used in Measurement While Drilling (MWD), Logging While Drilling (LWD) and wireline operations.

FIG. 1illustrates a downhole tool100having a cooling system110, according to example embodiments. As shown, the downhole tool100is within a borehole104that is drilled into the formation102. The cooling system110can be used with a drill string, a downhole wireline tool, a permanently installed downhole tool, or a temporary well testing tool, as further discussed below. From the Earth's surface to downhole, a drilling fluid may pass through a downhole tool string (including the downhole tool104) and out an end of the string. The drilling fluid may then return to the Earth's surface through an annulus105.

The cooling system110lowers temperatures of electronic components encloses in the downhole tool to a temperatures lower than the downhole ambient temperature. In an example, the cooling system110lowers temperature of a payload, such as a thermal component mounted on a board in the downhole tool100. In an option, the thermal component includes, but is not limited to, heat-dissipating components, heat-generating components, and/or heat-sensitive components. An example of a thermal component is an integrated circuit, e.g., a computer chip, or other electrical or mechanical device that is heat-sensitive, or whose performance is deteriorated by high temperature operation, or a device that generates heat. The cooling system110is installed within a cavity of the downhole tool100.

Referring toFIG. 2, the cooling system110includes a pressured container120that has refrigerant122, such as, but not limited to, water. Water is non-toxic and can be released into the drilling mud, and has a high specific heat of vaporization. For instance, about 3.5 gallons of water can provide continuous cooling power of about 20 W for 14 days. In another option, the refrigerant is isopropyl alcohol. The pressurized container120is, in an option, capable of withstanding the extreme downhole temperatures and shock conditions. For example, the pressurized container120can be a stainless steel container. In an option, the contents of pressurized container120are placed under pressure at the Earth's surface, prior to dropping the tool down the borehole. In another option, the pressure of the pressurized container120is created and/or maintained by downhole pressure, or by the flow of drilling mud. For instance, in an option, the pressurized container120includes a cylinder with a piston therein that is actuated by the downhole pressure. In another option, a compressible spring can be used. In a further option, the increased downhole temperature pressurizes the container120, for example when the container has a fixed volume. The refrigerant190continually exchanges heat with the ambient downhole temperature, for example, through the body of the container120. In an option, the pressurized container120includes one or more orifices, which allows for the refrigerant to exit the container120to a tank150. The refrigerant can be released at specific rates using a regulator, or with orifices of different sizes.

The cooling system110further includes a tank150in fluid communication with the pressurized container120. The tank150allows for the refrigerant to expand and cool the payload160, as further described herein. The tank150can be in various forms. For example, the tank150can be any expansion chamber, such as, but not limited to, tubes of the heat exchanger.

The cooling system110further includes a heat exchanger160thermally coupled with the thermal component or payload164. In an embodiment, the heat exchanger160is thermally coupled with the thermal component or payload164via a conductive path to the thermal component or payload164. In another option, the heat exchanger160may be thermally coupled with the thermal component12by radiation or convection. The heat exchanger160may be any appropriate type of heat exchanger, e.g., a conduction heat exchanger that uses heat conduction to transfer the heat through solids. The heat exchanger160may also comprise multiple layers of the same or different materials.

The heat exchanger160and the tank150are thermally coupled via a thermal conduit system. The thermal conduit system includes a thermally conductive material for transferring heat from the heat exchanger160to the tank150. The temperature gradient between payload164and the tank150is such that the tank150absorbs the heat from the payload164through the heat exchanger160and the thermal conduit system. The cooling system110removes enough heat to maintain the payload164at or below downhole ambient temperature. Absorbing heat discretely from the thermal component thus extends the useful life of the thermal component of the payload.

The tank150is in fluid communication with the pressurized container120. In an option, an actuator170is at an exit of the pressurized container120, and controls the timing and the amount of refrigerant that is released to the tank150. In an option, the actuator is actuated by an electrical circuit that activates a valve, such as a check valve124. In another option, it includes a static system. For instance, a plug that melts at a preset temperature can be used. In another option, a bimetallic strip can be used, and the strip would coil based on the temperature of the devices which need to be cooled. In another option, the temperature of the electronics could be sensed, and electronics can be used to turn on or off the cooling system or to regulate the size of the orifice.

The tank150is further situated adjacent a venturi180. The venturi180is located proximate to the pressurized container120, and has a drilling mud passage188therethrough. The drilling mud passage188has a first portion182and a second portion184, and a convergence186therebetween. Drilling mud190flows through the venturi180from the first portion182, through the convergence186, and through the second portion184. The venturi180, in an option, includes a sintered tungsten carbide nozzle and throat and a shallow angle can be created to reduce the impingement from the drilling mud. In another embodiment, the venturi180includes geometry which causes the flow of drilling mud to separate from the flow walls.

Due to the geometry of the venturi180, mud flowing therethough will experience an increase in velocity, and a decrease in pressure. The low pressure point creates low pressure near the tank150. Refrigerant122is kept under higher pressure in the container120, and is released to the tank150, where the refrigerant122gets flashed to a lower pressure, and the temperature of the refrigerant122drops below the downhole ambient temperature. The temperature drop can be used to cool a payload164via the heat exchanger160, as discussed above. The low pressure fluid can then be released in the drilling mud or piped up to the Earth's surface.

During a method of cooling a downhole tool, the method includes pressurizing a container having refrigerant, such as water, therein, disposing a pressurized container within a downhole tool string, and disposing the downhole tool string downhole in a wellbore. In an option, the container is pressurized prior to disposing the downhole tool string downhole in the wellbore, such as pre-pressurized at the Earth's surface. In a further option, creating or maintaining the pressure does not necessarily depend on downhole pressure or flow. Once the downhole tool is disposed downhole, the pressure of the pressurized container can be created or maintained, and refrigerant is maintained at the ambient temperature. The pressure can be maintained or provided using the downhole pressure, drilling mud flow, electrically (e.g. pump), mechanically (e.g. biasing member), or combinations thereof. For instance, a piston or spring or bellows can be displaced using downhole pressure and/or drilling mud flow. In another option, the pressure can be maintained by rotating a turbine with downhole mud flow.

The method further includes decreasing pressure of the drilling mud near the pressurized container within the downhole tool including flowing drilling mud through passage of a venturi. For instance, the drilling mud flows through a convergence, which increases the velocity of the fluid, and lowers the pressure of the drilling fluid. The refrigerant is flashed to a lower pressure due to a lower pressure from the drilling fluid, where the temperature of the refrigerant drops below the downhole ambient temperature, a payload of the downhole tool string is cooled to a temperature lower than the downhole ambient temperature. The low pressure refrigerant can be released into the drilling mud, or can be piped to an upper surface portion of the wellbore. In another option, the refrigerant can be collected in a tank and brought back to the surface.

In a further option, a regulator can be used to release the refrigerant from the pressurized container upon occurrence of an event. For instance, an operator can monitor certain conditions, and operate the regulator from the Earth's surface. Or the regulator can be operated when the temperature of the refrigerant is at or greater than the downhole ambient temperature.

Wellsite operating environments, according to some embodiments in which the above-described measurement techniques and systems can be used, are now described.FIG. 3illustrates a drilling well during Measurement While Drilling (MWD) operations, Logging While Drilling (LWD) operations or Surface Data Logging (SDL) operations, according to some embodiments. It can be seen how a system may also form a portion of a drilling rig402located at a surface404of a well406. The drilling rig402may provide support for a drill string408. The drill string408may operate to penetrate a rotary table410for drilling a borehole412through subsurface formations414. The drill string408may include a Kelly416, drill pipe418, and a bottom hole assembly420, perhaps located at the lower portion of the drill pipe418.

The bottom hole assembly420may include drill collars422, a downhole tool424, and a drill bit426. The drill bit426may operate to create a borehole412by penetrating the surface404and subsurface formations414. The downhole tool424may comprise any of a number of different types of tools including MWD (measurement while drilling) tools, LWD (logging while drilling) tools, and others.

During drilling operations, the drill string408(perhaps including the Kelly416, the drill pipe418, and the bottom hole assembly420) may be rotated by the rotary table410. In addition to, or alternatively, the bottom hole assembly420may also be rotated by a motor (e.g., a mud motor) that is located downhole. The drill collars422may be used to add weight to the drill bit426. The drill collars422also may stiffen the bottom hole assembly420to allow the bottom hole assembly420to transfer the added weight to the drill bit426, and in turn, assist the drill bit426in penetrating the surface404and subsurface formations414.

During drilling operations, a mud pump432may pump drilling fluid (sometimes known by those of skill in the art as “drilling mud”) from a mud pit434through a hose436into the drill pipe418and down to the drill bit426. The drilling fluid can flow out from the drill bit426and be returned to the surface404through an annular area440between the drill pipe418and the sides of the borehole412. The drilling fluid may then be returned to the mud pit434, where such fluid is filtered. In some embodiments, the drilling fluid can be used to cool the drill bit426, as well as to provide lubrication for the drill bit426during drilling operations. Additionally, the drilling fluid may be used to remove subsurface formation414cuttings created by operating the drill bit426.

FIG. 4illustrates a drilling well during wireline logging operations, according to some embodiments. A drilling platform486is equipped with a derrick488that supports a hoist490. Drilling of oil and gas wells is commonly carried out by a string of drill pipes connected together so as to form a drilling string that is lowered through a rotary table410into a wellbore or borehole412. Here it is assumed that the drilling string has been temporarily removed from the borehole412to allow a wireline logging tool body470, such as a probe or sonde, to be lowered by wireline or logging cable474into the borehole412. Typically, the tool body470is lowered to the bottom of the region of interest and subsequently pulled upward at a substantially constant speed. During the upward trip, instruments included in the tool body470may be used to perform measurements on the subsurface formations414adjacent the borehole412as they pass by. The measurement data can be communicated to a logging facility492for storage, processing, and analysis. The logging facility492may be provided with electronic equipment for various types of signal processing. Similar log data may be gathered and analyzed during drilling operations (e.g., during Logging While Drilling, or LWD operations).

The cooling system has scalability. To increase the cooling power of the system, the flow rate of water released from the high pressure tank is increased. To extend the operating range of the system, the volume of the container can be increased. Furthermore, the final temperature provided by the system can be varied of a wide range by changing the flashing or low pressure value.

In view of the wide variety of permutations to the embodiments described herein, this detailed description is intended to be illustrative only, and should not be taken as limiting the scope of the invention. What is claimed as the invention, therefore, is all such modifications as may come within the scope of the following claims and equivalents thereto. Therefore, the specification and drawings are to be regarded in an illustrative rather than a restrictive sense.