Abstract:
An enclosure for housing a transducer and electronics for disposal on a downhole tool. A transducer is disposed at an angle with respect to a longitudinal axis of the enclosure, wherein the enclosure contains a fluid surrounding the transducer. Enclosures also include transducers linked to motor means for selective rotation of the transducers within the enclosure. Enclosures with transducer arrays for phased or targeted signal transmission/detection.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims benefit of U.S. provisional application Ser. No. 60/594,830, filed May 10, 2005, which is herein incorporated by reference. 
    
    
     BACKGROUND 
     1. Field of the Invention 
     Implementations of various technologies described herein generally relate to the packaging or housing of various sources, sensors and electronics for use inside a wellbore. 
     2. Description of the Related Art 
     The methodology of housing or packaging sources, sensors, electronics, and general components has seen many changes as technologies and materials have improved over time. In the oil and gas industry, subsurface formations are typically probed by well logging instruments to determine the formation characteristics. Data is typically acquired using sources and sensors disposed on a downhole tool and either stored in downhole memory or transmitted to the surface. As used herein, the term “transducers” is understood to encompass devices capable of operation as sources and/or sensors, and is not to be limited to any one particular signal type (i.e., acoustic, gravity, electromagnetic, pressure, etc.). 
     In conventional logging operations, particularly in wireline applications, the transducers are often placed on the downhole tool such that they are exposed to the subsurface environment. In some implementations the transducers are mounted within a tool housing filled with a fluid, such as oil. A drawback with this methodology is that such implementations may require volume compensation for the oil. Such mechanisms often entail pistons or bellows that move in response to displacement of the oil as a result of pressure and temperature changes, which. Further, certain compensating components exposed to the downhole environment may need to be cleaned in between downhole trips to ensure that they function properly. Such mechanisms often entail pistons or bellows that move in response to displacement of the oil as a result of pressure and temperature changes, which then affects the mechanical complexity of the system. 
     However, in logging while drilling (LWD) or measuring while drilling (MWD) applications, the above methodology is not particularly suitable or reliable due to the harsh drilling environment, which may be characterized by high shock condition, high pressures and high temperatures. Consequently, the transducers and associated electronics are typically disposed inside the drill string and are thereby isolated from the harsh drilling environment, which is detrimental to their ability to serve their intended purposes. 
     A need remains for improved techniques to package and house transducers and electronics for subsurface use. 
     SUMMARY OF THE INVENTION 
     The invention provides an enclosure for disposal on a downhole tool. The enclosure comprises at least one transducer disposed at an angle with respect to a longitudinal axis of the enclosure: and an electronics board coupled to the at least one transducer, wherein the enclosure contains a fluid surrounding the at least one transducer. 
     The invention provides a downhole tool for subsurface disposal. The tool comprising an elongated support: an enclosure disposed on the support, the enclosure comprising: at least one transducer disposed at an angle with respect to a longitudinal axis of the enclosure; and an electronics board coupled to the at least one transducer; wherein the enclosure contains a fluid surrounding the at least one transducer. 
     The invention provides a method for packaging a transducer for subsurface disposal. The method comprises disposing the transducer within an enclosure at an angle with respect to a longitudinal axis of the enclosure, disposing an electronics board within the enclosure, coupling the electronics board to the transducer; and filling the enclosure with a fluid to surround the transducer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a downhole tool equipped with enclosures for containing transducers and electronics in accord with the invention. 
         FIG. 2  illustrates an enclosure in accord with the invention. 
         FIG. 3  illustrates a perspective view of the enclosure shown in  FIG. 2 . 
         FIG. 4  is a cross-section side view of an enclosure disposed in a downhole tubular in accord with the invention. 
         FIG. 5  shows a perspective view of a downhole tubular configured with enclosures and shields in accord the invention. 
         FIG. 6  shows a perspective view of another downhole tubular configured with enclosures in accord with the invention. 
         FIG. 7  is a schematic of a transducer electronics module and multiplexer module in accord with the invention. 
         FIG. 8  shows a downhole tubular equipped with the acoustic transducers of the invention. 
         FIG. 9  illustrates a downhole tool equipped with enclosures containing an array of transducers in accord with the invention. 
         FIG. 10  is a side view of an enclosure equipped with mechanically rotateable transducers in accord with the invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  illustrates a downhole tool  100  equipped with two enclosures  30 , each containing transducers and electronics in accordance with implementations of various technologies described herein. Although two enclosures  30  are illustrated in the figure, it should be understood that in some implementations more or less than two enclosures may be used. The tool  100  is shown disposed in a borehole  12  that penetrates an earth formation. The enclosures  30  may be disposed on the outside surface of the downhole tool  100 , which may be a drill collar, a wireline tool, casing, or any other oilfield equipment that may be deployed inside the borehole  12 . The enclosure may be made from metal, plastic (e.g., polyetheretherketone PEEK® from Victrex Manufacturing Limited of Lancashire, Great Britain), or any other suitable material. Preferred materials should be strong enough to withstand the high pressures and high temperatures encountered downhole and should allow for the passage or radiation of a signal (e.g., electromagnetic, acoustic, etc.) therethrough. 
     The downhole tool  100  includes a multi-axial electromagnetic antenna  91  for subsurface measurements and various electronics  92 ,  93  with appropriate circuitry. Other embodiments of the invention may be implemented incorporating only the enclosures  30 , without additional sources or sensors. The downhole tool  100  may be supported in the borehole  12  by a logging cable  95  for a wireline application or a drill string  95  for a while-drilling application. In a wireline application, the tool  100  may be raised and lowered in the borehole  12  by a winch which may be controlled by an assembly of surface equipment  98 , which may include a power supply, a recorder for recording the data and a computer for processing the data. The logging cable or drill string  95  may include conductors  99  that connect the downhole electronics  92 ,  93  with the surface equipment  98  for signal and control communication. The downhole electronics  92 ,  93  may include a source of electrical energy and downhole memory for storing signals as a function of time or depth. The downhole electronics  92 ,  93  may also interface with a telemetry module for transmitting measurement information to the surface in real time while drilling. Alternatively, the signals may be processed or recorded in the downhole tool  100  and the processed data may be transmitted to the surface equipment  98 . 
     The enclosures  30  may be disposed on the outside surface, or in a cavity or void, of the downhole tool  100  by any attachment techniques commonly known in the industry. For example, depending on the subsurface application, the enclosure can be affixed to the tool exterior using a suitable adhesive, retainer, fasteners and the like, or on an arm extending from the tool  100  (not shown). The enclosures  30  may be disposed on the tool  100  such that only a fraction or surface of the enclosure is exposed to the borehole  12  as desired. This can be accomplished by disposing the enclosures  30  in a cavity or void formed in the tool  100 . As shown in  FIG. 1 , only one surface of the enclosure is exposed to the borehole  12 . The implementation of  FIG. 1  shows the enclosures  30  linked to the multi-axial electromagnetic antenna  91  and/or various electronics  92 ,  93  by conventional communication means, such as cables, fiber optics, inductive couplings, or connectors. 
       FIG. 2  illustrates an enclosure  200  in accordance with implementations of various technologies described herein. The enclosure  200  may include a single transducer  210  or an array of transducers  210 . In one implementation, the transducers  210  may be acoustic transducers. As such, the transducers  210  may be configured to convert energy between electric and acoustic forms and may be adapted to act as a source or a sensor, or both. One skilled in the art will appreciate that other forms of transducers may be used in implementations of the invention (e.g. resistivity electrodes, pressure, gravity, light, and other source/sensor devices). 
     Sonic logging of earth formations entails lowering an acoustic logging instrument or tool (such as tool  100 ) into a borehole traversing the formation. The instrument typically includes one or more acoustic sources (i.e., a transmitter) for emitting acoustic energy into the subsurface formations and one or more acoustic sensors or receivers for receiving acoustic energy. The transmitter is periodically actuated to emit pulses of acoustic energy into the borehole, which travel through the borehole and into the formation. After propagating through the borehole and formation, some of the acoustic energy travels to the receivers, where it is detected. Various attributes of the detected acoustic energy are subsequently related to subsurface or tool properties of interest. 
     When implemented with acoustic transducers, the enclosures  200  of the invention can be used for sonic logging to provide valuable information regarding subsurface acoustic properties, which can be used to produce images or derive related subsurface characteristics. Acoustic waves are periodic vibrational disturbances resulting from acoustic energy that propagates through a medium, such as borehole fluid and subsurface formations. Acoustic waves are typically characterized in terms of their frequency, amplitude, phase, energy, shape, and speed of propagation. Subsurface acoustic properties of interest include compressional wave speed, shear wave speed, borehole modes, and formation slowness. Additionally, acoustic images may be used to depict borehole wall conditions and other geological features away from the borehole. These acoustic measurements have applications in seismic correlation, petrophysics, rock mechanics and other parameters related to water and hydrocarbon exploration. 
     Turning to  FIG. 2 , although only four transducers  210  are shown, it should be understood that any number of transducers may be used in implementations of the various technologies described herein. The transducers  210  may be made of any suitable materials known in the art, such as piezoelectric ceramic discs. The composition, shape and frequency properties of the transducers may vary depending on the particular application. In one implementation, each transducer  210  is made from lead metaniobate powder mix compressed and baked to form a ceramic disc of about 1 inch (2.54 cm) in diameter and with a natural resonance frequency of about 250 kHz. 
     The transducers  210  may be disposed on the enclosure  200  at an angle ranging from a few degrees to about 90 degrees from the longitudinal axis of the enclosure  200 , as shown in  FIG. 2 . The transducers  210  may also be closely spaced from each other within the enclosure  200 . 
     A backing element  220  may be coupled to the back surface of each transducer  210 . The backing element  220  may be formed in a similar shape to match the transducer  210 , for example in cylindrical shape if the transducer is disc shaped. The backing element  220  may be formed from any suitable material, such as rubber compounds and other known synthetic resins or mixtures, depending on the type of transducer used in a particular implementation. In an implementation using acoustic transducers, the backing element  220  can be made from conductive material. In the case of a transducer  210  activated as a receiver, the backing element  220  may act as an attenuator to decrease the ringing of the transducer  210  after it has been struck by an incoming sound wave. In some implementations, the backing element  220  may be configured to increase the bandwidth response of the transducer  210 . In some implementation, the backing element  220  may be replaced by an active, driven means of providing the attenuation (not shown). 
     The transducers  210  may be electrically coupled to an electronic board  230  (e.g. via wires  231 ), such as a printed circuit board (PCB), disposed adjacent the backing elements  220 . The electronic board  230  may provide amplification, filtering, digitization and may interface with other electronic circuits, such as electronics  92 ,  93 , which may be remotely disposed inside the downhole tool  100 . The electronic board  230  may include control and processing circuitry, memory, and stored logic for emitting ultrasonic pulses via the transducers  210  and for generating return signals representative of echoes that return to the transducers  210  that interact with and return from the borehole wall. As a result of placing the electronic board  230  near the transducers  210 , crosstalk between the transducers  210  and the electronic board  230  may be minimized, and interference with other circuits, such as power lines, may be reduced, thereby increasing the signal-to-noise ratio and reducing the amount of noise the measurement module may pick up from the other circuits. Signal communication to/from the electronic board  230  within the enclosure  200  and external devices in through a connector  280 . In some implementations, a bulkhead  310  (shown in  FIG. 3 ) may be used for connection with other circuits, e.g., electronics  92 ,  93 . The bulkhead  310  may be a pressure-proof multi pin bulkhead connector as known in the art.  FIG. 3  illustrates a perspective view of the enclosure  200  in accordance with implementations of various technologies described herein. 
     In one implementation, one side of the enclosure  200  facing the transducers  210  is formed including grooves or gaps  240  having a triangular cross section, as shown in  FIG. 2 . In some implementations, a wedge  250  may be disposed inside each groove  240  using an adhesive or any other attachment means commonly known in the art. The wedge  250  may be made form any suitable material that provides the desired signal transparency/properties. In one implementation, the wedge  250  may be made from polytetrafluoroethylene (PTFE) Teflon® from E.I. DuPont De Nemours &amp; Co of Wilmington, Del., USA. As shown in the implementation of  FIG. 2 , the wedge  250  is exposed to the exterior and may provide an optimal interface with well fluids for an acoustic transducer, given its sound velocity characteristics. As such, the wedge  250  may be used to maintain the linearity of the angle of incidence of acoustic waves entering the transducers  210 . 
     The enclosure  200  may further include a cover or lid  260  disposed on the opposite side of the grooves  240 . The lid  260  may include an O-ring seal that acts simply as a fluid barrier. In one implementation, the lid  260  may be made from the same material as the rest of the enclosure  200 , such as polyetheretherketone PEEK®. Implementation of the enclosure  200  may be formed in more than one piece (e.g. two halves) configured to fit together to form a closed unit.  FIG. 2  shows one implementation having a main body and a lid  260  with an O-ring to provide a sealed enclosure  200 . 
     The assembled enclosure  200  may further include a fluid  290 , such as a polymerized fluid, within its internal cavity to fill the voids and surround the various components such as the transducers  210 , backing elements  220 , and the electronic board  230 . The added fluid  290  aids in insulating the housed components from temperature extremes, from high pressures, in insulating conductors from one another, and in reducing shock to the components. In one implementation, the fluid  290  may be injected into the enclosure  200  after the lid  260  is affixed in place. In this case, a vacuum can be drawn from the enclosure  200  via a first valve  232  formed in the enclosure, while the fluid is injected via a second valve  233  in the enclosure (See  FIG. 3 ). Once filled, the valves  232 ,  233  can be sealed using oil-filling plugs or other means known in the art. In some implementations, the lid  260  for the enclosure  200  also acts as a compensator for volume changes in the fluid  290  due to temperature/pressure variations. The large surface area (relative to the walls of the enclosure), thinness, and flexibility of the lid  260  allow it to flex as the fluid volume changes. As shown in the cross-section of  FIG. 2  a lid  260  of the invention can be implemented with a thin recessed central section and a thicker perimeter to hold an O-ring to provide a seal. Other volume compensating means can be implemented with the enclosures of the invention as known in the art. 
     In one implementation, a polymerized gel is used as the filler fluid  290 . Suitable fluids include a silicon-based gel, such as Sylgard® 182 available from Dow Coming of Midland, Mich., USA. Subsurface temperatures and pressures may affect the fluid  290  volume within the enclosure  200 . In some implementations, the enclosure  200  may further include compensating means as known in the art to compensate for the volume changes of the polymerized gel  290  without adversely affecting the housed components. 
     The compact design and small component dimensions of the enclosures  200  of the invention allow one to construct a transducer unit that is smaller compared to conventional transducer packages. As such, the enclosures of the invention can be disposed on downhole tools in various ways.  FIG. 4  shows a side view of an enclosure  200  of the invention disposed in a downhole tool  100 . The enclosure  200  is in a recess  312  formed in the tool  100  wall. The enclosure  200  is coupled to a bulkhead  310  that ties into a passage  313 , also referred to as a feedthrough, for signal/power transmission between the transducers  210  and external components (e.g., electronics, telemetry, memory, etc.) via one or more leads  314  as known in the art. A shield  316  may be used to cover the enclosure as described below. 
       FIG. 5  shows a series of enclosures  200  disposed in a downhole tool  100 . Each enclosure  200  is disposed in a separate recess  312  formed substantially parallel to the longitudinal axis of the tool  100 . As mentioned above, shields  316  can be placed over the enclosures  200  for protection against abrasion and collision. The shields  316  may be formed of any suitable material and are preferably configured with one or more apertures  318 . The shields  316  can be affixed to the downhole tool  100  using any suitable means as known in the art. Another implementation can be configured with a plurality of enclosures  200  disposed in one elongated recess or void formed in the tool  100  wall (not shown). 
       FIG. 6  shows another implementation of the invention. The enclosures  200  are shown disposed in a downhole tool  100  equipped with stabilizer blades  320 . With this embodiment, the transducers  210  within the enclosures  200  can be maintained in direct contact with the borehole wall for more accurate measurements. Those skilled in the art will appreciate that the enclosures  200  of the invention can be disposed on downhole tools in many ways depending on the desired measurements and mode of tool conveyance within a borehole. For example, an enclosure  200  can be affixed to casing tubulars (inside or outside) using conventional fasteners or clamping means and linked by cable(s) for power/communication for long-term monitoring applications. 
       FIG. 7  shows a general schematic layout of an electronics module  32  that can be implemented in an electronic board  230  of the enclosures of the invention. The module  32  includes a preamplifier stage  101 , a filter stage  102 , an analog-digital converter (ADC) stage  104 , and a power amplifier stage  106 . The module  32  is shown linked to an n-to-1 multiplexer (MUX) unit  44  adapted to funnel “n” signals to one channel for output through lead  42 . A switch  108  linked to the transducer element  210  toggles between position  1  and position  2 . In position  1 , the transducer  210  is activated by the power amplifier stage  106  and the transducer is implemented as a transmitter. With the switch  108  in position  2 , the preamplifier stage  101  receives the analog acoustic energy signal detected by the element  210  and it is processed through the module  32  to implement a receiver. The small package and low power electronics module  32  integrated with the transducer  210  minimizes power consumption and improves noise reduction since digital signals are cleaner compared to analog signals. The digitized signal data can also be routed far distances for additional processing free of unwanted noise if desired. 
     The dual-purpose transducers (i.e., source-sensor)  210  of the invention allow for pulse echo measurements. As known in the art, the measurement of two-way travel time of a pulse echo signal reflected from the borehole  12  wall can be used to determine the borehole geometry, such as its radius or standoff.  FIG. 8  shows an implementation of the invention operating in a pulse echo mode. A downhole tool  100  is equipped with several axially and azimuthally distributed enclosures  200  of the invention. Using an electronic module  32 , the transducer(s)  210  within the enclosures  200  can be switched between modes to obtain the pulse echo measurements in the borehole  12 . The measured acoustic signal data can be processed using conventional techniques known in the art. 
       FIG. 9  shows another implementation of the invention. A downhole tool  100  is equipped with an enclosure  200  of the invention housing a series or bank of aligned transducers  210 . With this configuration, the transducers  210  can be activated in a timed or phased sequence for targeted and controlled measurements. For example, by timing their activation, the ‘angle’ of the transducers  210  can be varied electrically in such a way that signal beam/energy can be transmitted/received at the normal or at oblique incidence with reference to the borehole wall. Other implementations can be configured to achieve such phased array measurements (not shown). The timing and activation of the transducers  210  can be controlled by conventional software means and electronics on the electronic board  230 . 
       FIG. 10  shows a side view of another enclosure  200  implementation of the invention. In this configuration, the backing elements  220  are linked to an actuator rod  205  via individual hinged connecting rods  206 . The backing elements  220  are each mounted on individual axles  207  that allow the backing elements to pivot and rotate about a fixed axis such that the affixed transducer elements  210  can rotate in either direction. The actuator rod  205  includes a gear rack at one end to engage with a pinion gear  208  on a motor  209  mounted within the enclosure  200 , forming a rack-and-pinion gear system. The motor  209  can be activated to rotate in either direction to move the actuator rod  205 , which in turn pulls or pushes the connecting rods  206  to rotate the transducer elements  210  such that the element faces are positioned at a desired angle for targeted measurements. The motor  209  can be linked through the electronic board  230  for activation and control. It will be appreciated by those skilled in the art that various mechanical configurations as known in the art can be used to alter the position or angles of the transducers as desired in other enclosure implementations of the invention. 
     The technologies described herein may be implemented in various fields of use. They are not limited to subsurface applications. The application for acoustic transducers is just an example of the potential uses for this invention. The technologies described herein may be used to package all types of transducer devices, which can then be interfaced with power, control, or recording systems external to the enclosure  200 . It will also be appreciated that the transducers are not limited to operation within any specific frequency or frequency range. Various geometries described herein merely represent a small sample of the many potential applications and designs that are covered by implementations of various technologies described herein. For example, enclosures of the invention may be configured in various shapes other than rectangular unit (not shown). It will also be appreciated that the various technologies described herein may be implemented in any type of downhole tool or application, such as wireline, LWD/MWD, coiled tubing, casing tubulars, logging-while-tripping, logging-while-casing, reservoir monitoring, etc.