Patent Publication Number: US-8535026-B2

Title: Mechanical system for movement along a housing axis

Description:
FIELD OF THE DISCLOSURE 
     The subject disclosure generally relates to the field of sensors and more particularly to mechanisms used to move sensors along the length of a housing of an oilfield tool. 
     BACKGROUND OF THE DISCLOSURE 
     Oil exploration involves evaluating reservoirs to determine the movement or absence of oil, gas, or water as the reservoir fluids are produced. Understanding movement of gas in reservoirs is important to the prevention of premature breakthroughs and optimization of reservoir performance. It is known to use gravity borehole tools to measure characteristics of geologic formation, particularly in the exploitation of hydrocarbon reservoirs found in geologic formations or in the subsurface storage of carbon dioxide or water. 
     The process of measuring physical properties of earth formations beneath the surface of the earth is commonly referred to as “well logging”. It comprises the step of lowering sensors or testing equipment mounted on robust tool bodies into a wellbore drilled through the earth. When the tool is suspended from an armored cable the process is more specifically referred to as “wireline” well logging. Alternative conveyance techniques as known in the art include lowering the instruments mounted on drill pipe, casing or production tubing or on coiled tubing. The drill pipe conveyance technique, in particular, is known as “logging while drilling” when measurements are performed during the actual drilling of a wellbore. 
     Borehole gravity measurements are a direct measure of the bulk density of the formation surrounding a wellbore. Typically gravity data are taken at different vertical depths or stations along the wellbore. The basic principle of borehole gravity measurements is that the change in gravity relates directly to the bulk density contrast of the formation, the distance from the stations and the density contrast body. The bulk density in turn is directly related to grain densities and the pore fluid (gas, oil or water) densities and porosity of the formation. Several gravity measurement tools are commercially available. U.S. Pat. No. 5,970,787 to Wignall describes a tool for conducting gravimetric survey downhole in an earth formation. 
     One limitation to using gravity sensors is that the accuracy of the gravity measurement may be insufficient for making gravity density measurements in boreholes. Gravity sensors are extremely sensitive to vibrations and these vibrations may throw the gravity sensors out of calibration. Further, even if the sensor remains calibrated after being subjected to vibrations the sensor will take time to settle which is undesirable as it reduces the logging speed and increases the chance of having the tool stuck in the wellbore. Minimizing both noise and vibrations in the gravity measurements may increase this accuracy. 
     SUMMARY OF THE DISCLOSURE 
     In view of the above there is a need for an improved mechanism which permits movement of sensors along the length of a tool housing with a minimum of noise and vibrations. The subject technology accomplishes these and other objectives. The subject disclosure provides a drive system without traditional mechanical contacts e.g. metal to metal via gears, therefore, minimizing noise and vibrations in the gravity measurements. 
     In accordance with an embodiment of the subject disclosure, an apparatus comprising an elongated, hollow vessel is disclosed. The apparatus further comprises a fluid filled housing disposed inside the vessel with the housing defining a hydraulically isolated chamber. A pump member is disposed inside the hydraulically isolated chamber and an element is attached to the pump. The pump member provides a differential pressure which moves the pump member and element inside the length of the housing. 
     In accordance with a further embodiment of the subject disclosure, an apparatus comprising an elongated, hollow vessel with a fluid filled housing disposed inside the vessel is disclosed. The apparatus further comprises a housing defining a hydraulically isolated chamber and a pump member disposed inside the hydraulically isolated chamber and attached to the housing. Flexible tubing connecting the pump member to a port assembly having an element attached to the port assembly is also disclosed. Finally, the pump member provides a differential pressure thus moving the port assembly and element inside the length of the housing. 
     In accordance with a further embodiment of the subject disclosure, a method for moving an element inside a housing is disclosed. This method comprises disposing a fluid filled housing inside an elongated, hollow vessel and defining a hydraulically isolated chamber within the fluid filled housing. The method further comprises disposing a pump member inside the hydraulically isolated chamber and attaching an element to the pump. A differential pressure is provided by the pump member thus moving the pump member and element inside the length of the housing. 
     Further features and advantages of the subject disclosure will become more readily apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  illustrates a wellsite system in which the subject disclosure can be employed; 
         FIG. 2  illustrates one embodiment of the subject disclosure; 
         FIG. 3  illustrates the embodiment of  FIG. 1  shown in two different positions for use in taking sensor readings of a geological formation; 
         FIG. 4A-D  illustrates examples of hydraulic energy storage devices; 
         FIG. 5  illustrates a further embodiment of the subject disclosure; 
         FIG. 6  illustrates an embodiment of the subject disclosure comprising a cable position transducer; and 
         FIG. 7  illustrates a further embodiment of the subject disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The present technology is directed to a mechanism for moving objects along the axis of a confining cylinder. More particularly, the present technology is directed to a mechanical system for moving sensors in a longitudinal direction in a housing of an oilfield tool. The direction of motion of the mechanism is in the longitudinal direction of the oilfield tool. 
     Embodiments of the present technology comprise a pump. In one non-limiting example, the pump is a bidirectional pump with a first outlet for pumping fluid to operate the system in a first direction and a second outlet for pumping fluid to operate the system in a second direction. These bidirectional pumps are commercially available. In non-limiting examples, these bidirectional pumps may be positive displacement pumps for example, a progressing cavity pump. As will be apparent to one skilled in the art, any commercial available bidirectional pump may be used. Typically, electrical, hydraulic or pneumatic means are used in energizing these pumps. The pump moves an object along the axis of a housing. In one non-limiting example the housing is a confining cylinder and may be the housing of an oilfield tool, e.g., wireline or drilling tool. One skilled in the art will recognize that the subject disclosure has numerous non-oilfield applications for example, pneumatic tube systems used at drive-in banks for transporting cash and documents between the customer and the teller. The housing may be a drill collar or any other type of tubular structure that may be used to package an oilfield tool for example, a wireline tool, LWD tool or a tool moving inside a cased well for example, an intelligent “plug” comprising additional measurement tools capable of moving down the well by itself, instead of being pumped down the wellbore, e.g., cement plug. The element to be moved is attached to one side of the pump. The element is physically attached to the pump utilizing methods which are known to those skilled in the art which include in non-limiting examples welded, screwed or pinned. In one non-limiting example the element is a sensor, for example, a gravity sensor. The housing is filled with a fluid which may be pumped by the pump in either direction. The fluid may comprise any gas or liquid. In non-limiting examples the fluid may be one of oil or water or both oil and water. The pump moves fluid from the bottom to the top or vice versa within the housing. When the pump moves fluid from the bottom to the top, the pressure on the bottom decreases and the pressure on the top increases, resulting in a net downwards force on the pump-element assembly. The assembly will move downwards until the pressure equilibrates on the top and bottom. The pump direction can be reversed therefore moving the pump-object assembly in the opposite direction. 
     In one non-limiting example the apparatus comprises a sensor attached to a pump. The apparatus is located in a tool housing. The first and second outlets of the pump are located above and below a seal and in one non-limiting example the seal is a dynamic seal which seals between the pump-sensor assembly and the housing. In non-limiting examples these dynamic seals comprise elastomeric materials or polymers for example Teflon. In other examples these dynamic seals may comprise a plurality of different materials. The housing is filled with a fluid and the fluid can be pumped through the pump in either direction. The pump is attached electrically to the housing via a flexible cable. The cable in one non-limiting example may be a helical electrical line. The cable is flexible to accommodate the length change when the apparatus moves from a first position to a second position. The cable also provides electrical continuity of the pump/sensor assembly with the housing which ensures power is provided into the pump/sensor assembly and a signal can be transmitted between the pump/sensor assembly and the housing. The flexible cable provides a connection to a control unit for the apparatus which controls the pump/sensor assembly within the housing. Referring now to the drawings, in which like numerals represent like elements through the several figures, aspects of the subject disclosure will be described. 
       FIG. 1  illustrates a diagrammatic illustration of the apparatus of the present disclosure wherein a wellbore tool  107  is diagrammatically illustrated in a borehole  113  below the surface of the earth  115  which is cased  103 . In  FIG. 1 , the section  117  includes a geological formation  109 , which is of interest as to its overall thickness and potential as to oil and gas production or mineral bearing content. The wellbore tool  107  is attached to a cable e.g. a wireline cable which is used to raise and lower the wellbore tool  107  within the borehole  113 . The diagram depicts a diagrammatic illustration of the apparatus of the present disclosure in use within a cased borehole but the apparatus could also be employed in an uncased borehole. The wellbore tool  107  comprises a housing  111  connected to a pump/sensor assembly  119  via a flexible cable  105 . Although,  FIG. 1  shows the wellbore tool in a vertical borehole  113 , it should be clear that the present disclosure is not limited to a vertical borehole  113  but can be used in a deviated or horizontal borehole. 
       FIG. 2  illustrates one embodiment of the present disclosure in more detail. The housing  201  can be deployed in the wellbore tool  107 . The housing comprises a fluid  211  which can be pumped through the pump in either direction. The housing  201  is hydraulically isolated from the borehole. The housing  201  further comprises a pump/sensor assembly  213 . The pump  215  which in one non-limiting example is a bidirectional pump has inlets/outlets  205  with a dynamic seal  209 . A sensor  203  which will move along the length of the housing is attached to the pump  215 . The pump  215  provides the thrust to move the pump/sensor assembly  213  inside the length of the housing  201 . The pump/sensor assembly  213  can be compared to an elevator assembly moving along the length of the housing  201 . The distance the pump/sensor assembly  213  moves will be limited by the length of the housing. Displacement of the pump/sensor assembly  213  is achieved by the fluid  211  moving from one side, upper or lower of the pump/sensor assembly  213  to the other upper or lower side of the pump/sensor assembly  213 . Referring to  FIG. 2  when fluid is moved from the upper to lower portion of the housing the pump/sensor assembly  213  is moving up. Conversely, when fluid is pumped from the lower to the upper portion of the housing the pump/sensor assembly  213  is moving down. Movement of the pump/sensor assembly  213  can be controlled by adjusting the volume of the fluid which is being pumped. Further, the direction of movement can also be controlled by adjusting the volume of the fluid which is being pumped. The pump/sensor assembly  213  is maintained at a given position along the axis of the housing  201  by the pump  215  which sets the pressure of the fluid P 1  and P 2  to balance the buoyant weight of the pump/sensor assembly  213 . In certain instances, it may also be desirable to match the density of the fluid to the density of the pump/sensor assembly  213  in order to achieve neutral buoyancy thus maintaining the apparatus in a stationary position when the pump is shut down. The pump  215  is attached to the housing with a flexible cable  207 . 
       FIGS. 3A and 3B  illustrate movement of the pump/sensor assembly  213  within the housing  201 . The pump  215  enables this movement within the housing  201  by pumping fluid from one side of the pump/sensor assembly  213  to the other. In  FIG. 3A , the pump  215  moves fluid from a first chamber  309  to a second chamber  307  and is depicted in  FIG. 3A  as fluid moving from the bottom to the top  311 . As the fluid moves in the direction of  311 , the pressure P 1  in chamber  307  increases and the pressure P 2  in chamber  309  decreases. This results in a net downward force on the pump/sensor assembly  213 . This pump/sensor assembly  213  moves in the direction  313  which is depicted as downwards in  FIG. 3B . The pump/sensor assembly  213  moves from a first position  303  to a second position  305  by a distance of Δz. The pump/sensor assembly  213  moves in the direction  313  until the pressure difference matches the buoyant weight of the pump/sensor assembly  213 . Movement of the pump/sensor assembly  213  in the direction  313  causes the flexible cable  207  to stretch. Similarly, movement in the opposite direction would adjust the flexible cable  207  and return the cable to its original position. 
     Environmental changes and fluid leakage from the housing  201  may cause the first chamber  309  and second chamber  307  to have varying pressure while the pump/sensor assembly  213  is stationary. This in turn may result in a shift in the sensor position  203 . The pump  215  may be utilized to correct the shift but in certain instances it may be advantageous to maintain an idle operation which will reduce mechanical or electromagnetic noise on the sensor  203 . The pump/sensor assembly  213  may further comprise one or a plurality of devices which will rigidly lock the pump/sensor assembly  213  to the housing  201 . The sensor position will therefore not shift as a result of vibration or mechanical shock therefore providing increased accuracy. Some non-limiting examples of these devices are hydraulic energy storage devices, valves or a physical locking mechanism. 
       FIGS. 4A-4D  depicts examples of hydraulic energy storage devices. These hydraulic energy storage devices can be used to maintain a pump idle operation when the pump/sensor apparatus has traveled the length of the housing  201  and reached the end of the housing. These hydraulic energy storage devices will prohibit a shift in the sensor position  203  which may arise due to environmental changes or fluid leakage. These hydraulic energy storage devices can be hydraulically connected to the first chamber  309  or the second chamber  307 . In alternative embodiments one or a plurality of energy storage devices can be connected to the first chamber  309  or the second chamber  307 . A “hydraulic accumulator” refers to a hydraulic device that is able to store potential energy.  FIG. 4A  depicts a spring biased piston hydraulic accumulator. The dynamic seal  401  and movable piston  403  in the spring biased piston accumulator separates two chambers, one adapted for containing a working fluid  415  and the other adapted for containing wellbore or atmospheric fluid  407 . In this instance the compressible medium is a spring  405 . Alternatively, the compressible medium can be a compressible fluid as in  FIG. 4B . As working fluid is pumped into the first chamber  309  or the second chamber  307  the movable piston  403  moves against the compressible medium, e.g., spring and stores potential energy. As the compressible medium compresses, the working fluid  415  pressure exceed the wellbore pressure  407 . This force provides a locking mechanism for the pump/sensor apparatus  213 . The locking mechanism functions when the working fluid chamber has a higher pressure than the wellbore or atmospheric fluid chamber. At some later point in time, the pressurized fluid in the chamber can be released to allow the compressible medium, e.g., spring  405  to move the piston  403  in the other direction. 
       FIG. 4B  depicts a compressible fluid charged piston. Similarly, when fluid is pumped into the reservoir the piston  403  moves against the compressible fluid  409 . As the compressible fluid  409  compresses the working fluid  415  pressure exceed the wellbore pressure  407 . This compressible fluid force similar to the spring force provides a locking mechanism. An example of a compressible fluid which may be used is nitrogen gas. 
       FIGS. 4C and 4D  depict a metal bellow accumulator. The metal bellow accumulator comprises a pressure vessel with a metal bellows assembly separating the working fluid from either wellbore or atmospheric fluid in  FIG. 4C  and compressible fluid e.g. nitrogen in  FIG. 4D . 
       FIG. 5  depicts one embodiment of the subject disclosure utilizing a hydraulic energy storage device. A hydraulic energy storage device is located on either side of the pump/sensor apparatus  213 . The movable piston  507  is provided in a chamber  509  defined inside the housing  201 . The piston is moveable in a longitudinal direction (indicated as of x) of the hydraulic energy storage device. 
     The working fluid  415  is compensated to wellbore or atmospheric fluid  407 . As the fluid moves in the direction of  511 , the pressure P 1  in chamber  307  increases and the pressure P 2  in chamber  309  decreases. This results in a net downward force on the pump/sensor assembly  213 . This pump/sensor assembly  213  moves in the direction  515  which is depicted as downwards in  FIG. 5 . The working fluid is in hydraulic communication with both of the hydraulic energy storage devices and both hydraulic energy storage devices are in hydraulic communication with the wellbore  501 . As discussed above when the working fluid is pumped into the first chamber  309  the movable piston  507  moves against the compressible medium, in this instance a spring and stores potential energy. As the compressible medium compresses the working fluid pressure  415  exceeds the wellbore pressure  407 . This force provides a locking mechanism for the pump/sensor apparatus  213 . When the pump/sensor assembly  213  reaches the end of the housing indicated as  513  the hydraulic energy storage device will maintain the pump/sensor assembly  213  in this position by locking the pump/sensor assembly  213  into this position. 
     Frictional losses may occur between the dynamic seals and the housing or in fluid viscous losses. Reducing frictional loss requires an increase in the pressure differential. Frictional losses may be used advantageously to dampen vibrations of the pump/sensor assembly as the pump/sensor assembly may continue movement even after the pressure has equilibrated and possibly “overshot” the targeted position. 
     In order to obtain a position of the sensor inside the housing relative to the top or bottom of the housing a number of devices can be used. One such device is an optical encoder wheel which is held in contact with the housing. The encoder wheel provides a means for monitoring the position of the sensor inside the housing. The encoder wheel turns when the pump/sensor assembly  213  moves and this turning of the wheel is interpreted as a change in position of the pump/sensor assembly  213 . A further method for monitoring the position of the sensor inside the housing comprises determining the amount of fluid displaced by the pump which in turn would determine how much the pump/sensor assembly had moved. Other methods that may be utilized to monitor the position of the sensor inside the housing include optical or acoustic methods e.g. ultrasonic which may be mounted on the housing or the pump/sensor assembly.  FIG. 6  depicts a further mechanism which may be utilized to monitor the position of the sensor inside the housing. The mechanism comprises a cable position transducer  603  connected via a cable  601  to the pump/sensor assembly  213 . The cable position transducer  603  may be located in the first chamber  309  or the second chamber  307 . A variety of other devices may also be used to monitor the position of the sensor inside the housing which includes a linearly variable differential transducer (LVDT), linear potentiometer, or any type of linear measurement technique may be used to measure and control the position of the sensor. In order to control the position of the pump/sensor assembly  213 , the measurements obtained by any of the devices mentioned above may be provided via real-time feedback to the housing. This will allow for real-time control of the movement of the pump/sensor assembly  213 . 
       FIG. 7  depicts a further embodiment of the present technology. The pump  701  is attached to the housing  705 . The mechanism further comprises a flexible tubing  703  connecting the pump  701  to a port  707 . The port  707  allows the working fluid to flow from the lower chamber up through the flexible tubing into the pump or vice versa. The pump remains stationary which may be desirable in certain applications. 
     Embodiments of the present disclosure may be used wherever the position of an object e.g. sensor is desired to be changed along the axis of a housing, for example, the housing of a tool. A number of sensors which may utilize the present disclosure include the following: A gravity tool which measures gravity at one location and then the sensor is moved a known distance along the borehole axis and gravity is measured again. The change in gravity over the known change in position can be used to measure density. In the case of either an electromagnetic or sonic tool a variable depth of investigation can be achieved by moving the transmitter or receiver along the axis of the borehole using the subject technology. Finally, in situations where measurements are needed without stopping the movement of a toolstring the subject technology may be useful. The pump/sensor assembly  213  may move in the direction opposite the toolstring at the same speed as the toolstring. In situations where tool sticking may occur and the operator of the tool wants to avoid stopping which is common for both wireline logging and drilling measurements the subject technology may be advantageous. 
     While the subject disclosure is described through the above exemplary embodiments, it will be understood by those of ordinary skill in the art that modification to and variation of the illustrated embodiments may be made without departing from the inventive concepts herein disclosed. Moreover, while the preferred embodiments are described in connection with various illustrative structures, one skilled in the art will recognize that the system may be embodied using a variety of specific structures. Accordingly, the subject disclosure should not be viewed as limited except by the scope and spirit of the appended claims.