Abstract:
A packer set monitoring and compensation system and method according to which the compression of the packer is sensed and a corresponding output signal is generated. The compression of the packer is changed in response to the sensed compression deviating from a predetermined value.

Description:
BACKGROUND  
         [0001]    Downhole packers are commonly used in many oilfield applications for the purpose of sealing against the flow of fluid to isolate one or more portions of a wellbore for the purposes of testing, treating, or producing the well. The packers are suspended from a tubing string, or the like, in the wellbore, or in a casing in the wellbore, and extend between the inner surface of the wellbore, or casing and the outer surface of the carrier tubing. Each packer includes one or more elastomer elements which are activated, or set, so that the packer elements are forced against the inner surface of the wellbore, or casing, and the outer surface of the carrier tubing, and compressed to seal against the flow of fluid and therefore to permit isolation of certain zones in the well.  
           [0002]    Under normal circumstances the packer elements retain their compression, or set, for a significant duration. However, packers often suffer from “set loss” in which they lose their compression for a number of reasons including, for example, an improper setting, material creep, and the like. This compromises the integrity of the seal and can lead to downhole leakage, requiring a workover operation which is expensive and time-consuming.  
           [0003]    Some prior art techniques have addressed this problem by determining in a laboratory the amount of compression required to correctly set a given packer design, under the assumption that similar conditions are present downhole. However, in many instances the packer setting process (loading rate, for example) and conditions (such as the presence of fluids, debris, and the condition of the tubing/casing inner diameter and the surface) cannot be replicated in the laboratory. As a result, the actual setting behavior of the packer may be different from that experienced in the laboratory and the problem is not solved.  
           [0004]    Therefore, what is needed is a system that can monitor the packer and compensate for set loss without having to resort to laboratory testing. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0005]    [0005]FIG. 1 is a sectional view of a packer utilized in an embodiment of the invention.  
         [0006]    [0006]FIGS. 2 and 3 are diagrammatic views of a monitoring and compensating system for the packer of FIG. 1. 
     
    
     DETAILED DESCRIPTION  
       [0007]    Referring to FIG. 1, a downhole tool is referred to, in general, by the reference numeral  10  and is shown installed in a casing  12 . It is understood that the casing  12  is disposed in a well and that the tool  10  is lowered to a predetermined depth in the casing  12  as part of a workstring, or the like, (not shown) which often includes other tools used to perform various oil recovery and completion operations.  
         [0008]    The tool  10  includes a tubular member  14  connected as part of the workstring and a packer  16  surrounds a portion of the outer surface of the tool  10  and consists of a series (in the example shown, three) of axially-spaced, annular packer elements  16   a ,  16   b , and  16   c . The packer elements  16   a ,  16   b , and  16   c  can be fabricated, at least in part, from an elastomeric material so that they can be compressed, in a manner to be described.  
         [0009]    The packer  16  also includes a series (in the example shown, two) of annular, axially-spaced anchoring slips  20   a  and  20   b  that are also disposed on the outer surface of the tubular member  14  downstream and slightly spaced from the packer elements  16   a ,  16   b , and  16   c . The anchoring slips  20   a  and  20   b  can be fabricated from a relatively hard material which is adapted to engage the inner wall of the casing  12 , as will be described.  
         [0010]    Two annular backup shoes  24   a  and  24   b  are disposed at the upper end of the upper packer element  16   a  and the lower end of the lower packer element  16   c , respectively, as viewed in FIG. 1. The backup shoes  24   a  and  24   b , when installed, compress the packer elements  16   a ,  16   b , and  16   c  during the packer setting process.  
         [0011]    Since the packer elements  16   a ,  16   b , and  16   c ; the anchoring slips  20   a  and  20   b ; and the backup shoes  24   a  and  24   b  all are conventional and are connected to the tubular member  14  in a conventional manner they will not be described in further detail.  
         [0012]    [0012]FIG. 2 depicts the packer  16  connected to a monitoring and compensating system, including a sensor  30  mounted between the upper backup shoe  24   a  and the corresponding end of the packer element  16   a  to measure, or sense, the amount of compressive stress on the packer element  16   a . The sensor  30  can be in the form of a strain gage, for example, in which case it could be mounted on the backup shoe  24   a ; or it could be in the form of a pressure sensor, for example, in which case it could be mounted on the corresponding end of the packer element  16   a . Thus, if there is a change in the packer set, i.e., a change in the amount of compressive stress on the packer elements  16   a ,  16   b , and  16   c , which normally would be a reduction in the stress, this change is detected by the sensor  30  which outputs a corresponding electrical signal, in a conventional manner.  
         [0013]    The sensor  30  is connected in an electrical circuit including a controller  32  and a solenoid operated valve  34  connected in series by conventional electrical conductors in a conventional manner. The controller  32  can be a classical PID controller or an adaptive controller and, as such, receives the above output signal from the sensor  30  and compares the signal with a desired threshold value or a “set-point” which corresponds to a reduction in the compression of the packer element  16   a  from its original set, or a predetermined reduction from its original set. If the signal falls below the set-point, the controller  32  generates an output signal which is passed to the valve  34 . The valve  34  is normally closed but is adapted to open when it receives the above signal from the controller  32 .  
         [0014]    The valve  34  is part of an apparatus which increases the compression of the packer  16  and which also includes a conduit system  36  through which fluid from a source  38  flows. The valve  34  is connected in the conduit system  36  and controls the flow of the fluid through the conduit system  36 , and a fluid compressor  40  is also connected in the conduit system  36  downstream of the valve  34 . The compressor  40  can be of any conventional design such as, for example, a piston mounted for reciprocal movement in a cylinder to compress the fluid. The compressor  40  is adapted to receive the fluid from the source  38  and increase the pressure of the fluid, and can be activated automatically upon receipt of the fluid, or it can be activated by the controller  32  in a conventional manner.  
         [0015]    A cavity is formed in the packer element  16   a  and is connected to the compressor  40  by the conduit system  36 . Thus, pressurized fluid flows from the compressor  40  to the cavity in the packer element  16   a  to increase its compression, or set, and thus compensate for the reduction in the compression sensed by the sensor  30 . The flow can continue in this manner until the set of the packer  16  is re-established. A check valve  42  is provided in the conduit system  36  for preventing the flow of fluid from the packer element  16   a  back to the compressor  40 .  
         [0016]    In operation, the packer  16  is located at a predetermined location in the casing  12  and is set, or activated, in a conventional manner. This causes the packer elements  16   a ,  16   b , and  16   c  to be forced against the inner wall of the casing  12  as well as the outer wall of the tubular member  14  in compression and, along with the anchoring slips  20   a  and  20   b , to engage the inner surface of the casing  12 . A seal is thus formed against the flow of fluids in the annular space between the outer surface of the tubular member  14  and the inner wall of the casing  12  which isolates the corresponding zone in the well.  
         [0017]    The sensor  30  continuously monitors the compressive stress on the packer element  16   a  and outputs a corresponding signal. If the output signal falls below the set-point value described above, the controller  32  generates a corresponding output signal which is passed to the valve  34  and causes the valve to open and fluid to flow though the conduit system  36 , as indicated by the flow arrows. The pressure of the flowing fluid is increased by the compressor  40 , and the pressurized fluid is passed to the cavity in the packer element  16   a  to increase its compression and re-establish its set. When the compressive stress on the packer element  16   a  returns to normal, as sensed by the sensor  30 , the controller  32  responds to a corresponding signal from the sensor  30  and closes the valve  34 .  
         [0018]    Although not shown in the drawings for the convenience of presentation, it is understood that the sensor  30  can be embedded in the packer element  16   a ; mounted on, or embedded in, the packer elements  16   b  and  16   c ; or mounted on either backup shoe  24   a  or  24   b . In the event multiple sensors  30  are provided in accordance with the foregoing they could be connected in the above electrical circuit, including the controller  32 , or connected in separate, identical, electrical circuits. In either case, the electrical circuit, including the sensor  30 , the controller  32 , the valve  34 , and the associated electrical conductors can also be either mounted on, or embedded in, the packer element  16   a  or mounted on either backup shoe  24   a  or  24   b . Thus, the operation described above in connection with the packer element  16   a  is equally applicable to the packer elements  16   b  and  16   c.    
         [0019]    An alternate embodiment of the monitoring system is shown in FIG. 3 in connection with the tool  10  of the embodiment of FIG. 2. According to the embodiment of FIG. 3, an actuator  50  is provided which includes a piston  52  mounted for reciprocal movement in a cylinder  54  in a conventional manner. One end of an actuator rod  56  is connected to an end of the piston  52  and extends though the housing of the cylinder  54 . The other end of the actuator rod  56  is connected to the backup shoe  24   a  of the tool  10 .  
         [0020]    A fluid line  58  connects a fluid source  60  to the inlet of a hydraulic pump  62 . A fluid line  64  extends from the outlet of the pump  62  into the chamber of the cylinder  54  defined, in part, by the piston  52 ; and a check valve  66  is disposed in the line  64  to prevent fluid flow from the chamber to the pump  62 .  
         [0021]    An electrical motor  68  is operatively connected to the pump  62  for driving it to pump fluid from the source  60 , via the line  58 , through the pump  62 , and, through the line  64  to the chamber of the cylinder  54 , as indicated by the flow arrows.  
         [0022]    An electrical circuit is provided which includes a sensing unit  70  connected to the line  64 , and a controller  72  electrically connected in series between the sensing unit  70  and the motor  68 . The sensing unit  70  senses pressure in the line  64  in a conventional manner and outputs a corresponding signal to the controller  72 . The controller  72  is identical to the controller  32  of the previous embodiment and, as such, is adapted to control the operation of the motor  68  in response to the signals received from the sensing unit  70  in a manner to be described.  
         [0023]    In operation of the embodiment of FIG. 3, the packer  16  is located at a predetermined location in the casing  12  and is set, or activated, in a conventional manner. This causes the packer elements  16   a ,  16   b , and  16   c  to be forced against the inner wall of the casing  12  as well as the outer wall of the tubular member  14  in compression. The backup shoe  24   a  is forced against the packer element  16   a , and the anchoring slips  20   a  and  20   b  are forced against the inner wall of the casing  12 . A seal is thus formed to prevent the flow of fluids in the annular space between the outer surface of the tubular member  14  and the inner wall of the casing  12  which isolates a corresponding zone in the well.  
         [0024]    The motor  68 , and therefore the pump  62 , are normally inactive, and the sensing unit  70  continuously monitors the fluid pressure in the chamber of the cylinder  54 , via the fluid line  64 , and outputs a corresponding signal. If the compression of the packer element  16   a  is reduced from its original set, the actuator rod  56 , and therefore the piston  52 , move downwardly, as viewed in FIG. 3. This, in effect, enlarges the chamber in the cylinder  54  and causes an attendant reduction in the fluid pressure in the chamber and in the line  64 . This reduced pressure is sensed by the sensing unit  70  and a corresponding signal is outputted from the sensing unit  70  to the controller  72 . The controller  72  compares the signal received from the sensing unit  70  with a desired threshold value, or “set-point”, of the fluid pressure in the chamber, which corresponds to a reduction in the compression of the packer element  16   a  from its original set, or a predetermined reduction from its original set. If the signal received from the sensing unit  70  falls below the set-point, the controller  72  generates an output signal which is passed to the motor  68  to activate the motor  68  and drive the pump  62 . Fluid is thus pumped from the source  60 , through the lines  58  and  64  and the pump  62  and to the chamber of the cylinder  54  to increase the pressure in the chamber and cause the piston  52 , and therefore the actuator rod  56 , to move in a downwardly direction, as viewed in FIG. 3. This, in turn, forces the backup shoe  24   a  further against the packer element  16   a  to increase its compression and re-establish its set. When this is achieved, the fluid pressure in the line  64  is increased to the extent that the sensing unit  70  outputs a corresponding signal to the controller  72  which, in turn, deactivates the motor  68  and therefore the pump  62 .  
         [0025]    Thus, according to the embodiments of FIGS. 2 and 3, any set loss of the packer  16  exceeding a predetermined valve is immediately determined and compensated for to insure that the original set conditions of the packer  16  are maintained.  
         [0026]    It is understood that although components of the system of the embodiments of FIGS. 2 and 3 are shown diagrammatically, and therefore out of scale, for the convenience of presentation, they can be located downhole in the casing  12  or the wellbore.  
         [0027]    It is understood that variations may be made in the foregoing without departing from the scope of the invention. For example, the casing  12  can be eliminated and the tool  10  can be inserted directly in the well. Also, the anchoring slips  20   a  and  20   b  can extend upstream from the packer elements  16   a ,  16   b , and  1   6   c . Further, the controllers  32  and  72  can respond to increases or decreases in the compression of the packer  16  from a predetermined value, and generate a corresponding output signal. Still further, in the unlikely event that the compression of the packer  16  needs to be decreased, fluid can be withdrawn from the cavity in the packer  16  and from the cylinder  54  as needed. It is also understood that spatial references, such as “downwardly”, “downstream”, “between”, etc., are for the purpose of illustration only and do not limit the specific orientation or location of the components or fluid flow described above.  
         [0028]    The foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and its practical application, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto and their equivalents.