Abstract:
A system and method for stimulating a formation surrounding a well and vibrating a device for supporting a gravel pack in the well, according to which a build up of scale on the device is sensed and a corresponding signal is output. A driver is provided for driving a transducer coupled to the device for vibrating the device and removing scale from the device.

Description:
BACKGROUND  
       [0001]     This invention relates to a vibrating device for use in sand control and formation stimulation in an oil and gas recovery operation.  
         [0002]     Many oil and gas downhole recovery operations, especially high-rate, high-permeability completions, produce reservoir fluids that contain fines, or formation sand. Therefore, support and screening devices, such as screens, slotted liners, and the like, have been utilized to support gravel packs, or the like, in the well to stabilize the formation while permitting the recovered fluids to pass from the formation into the wellbore while preventing passage of fines or formation sand with the recovered fluids.  
         [0003]     These support devices are often placed in a pressure-drop zone that subjects the devices to contamination from scaling (salt crystal growth) and other materials that are precipitated during production of the reservoir fluids (hereinafter collectively referred to as “scale”). Thus, the scale must be removed from the devices either mechanically, which adds to the labor and cost of the project, or chemically, which may harm the metal parts of the devices. Also, during the recovery operation from the wellbore, a “skin” develops around the wall of the wellbore that impedes the flow of fluid from the formation thus requiring techniques to remove the skin.  
         [0004]     Therefore, what is needed is a device of the above type that simultaneously performs the above screening as well as the scale and skin removal functions, yet eliminates the above problems.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0005]      FIG. 1  is a diagrammatic view of an embodiment of a sand control system of the present invention shown in a downhole environment.  
         [0006]      FIG. 2  is a flow chart depicting steps of a method according to an alternate embodiment of the invention  
         [0007]      FIG. 3  is a graph depicting two variables in accordance with the embodiment of  FIG. 2 . 
     
    
     DETAILED DESCRIPTION  
       [0008]     Referring to  FIG. 1  of the drawings, the reference  10  refers, in general, to a wellbore  10  that penetrates a producing formation F. It is also understood that a casing (not shown) can be provided in the wellbore  10  and that production tubing (not shown) is installed in the wellbore  10 .  
         [0009]     Four axially-spaced, cylindrical gravel pack support and screening devices  12   a - 12   d  are mounted, in any conventional manner, to the wall of the wellbore  10  adjacent the formation F. The devices  12   a - 12   d  can be in the form of screens, slotted liners, or any similar type of gravel support device. Although not clear from the drawing due to scale limitations, it is understood that the devices  12   a - 12   d  define an annular space with the wall of the wellbore  10  that receives one or more gravel packs, or the like, (not shown). The purpose of each gravel pack is to improve the integrity of the wall of the wellbore  10 , yet allow recovered fluids to pass to and through the devices  12   a - 12   d  and into the wellbore, while preventing the passage of fines or sand from the fluids. Since these gravel packs are conventional, they will not be described in any further detail.  
         [0010]     Two electrical drivers  16   a  and  16   b  are mounted on the inner wall of the device  12   b  in a diametrically opposed relationship. The drivers  16   a  and  16   b  are conventional and, as such, are connected to a source of AC or DC power in a manner to be described and are adapted to supply electrical power, for reasons to be described.  
         [0011]     A transducer  20   a  is mounted on the wall of the wellbore  10  between the devices  12   a  and  12   b ; a transducer  20   b  is mounted on the wall of the wellbore  10  between the devices  12   b  and  12   c ; and a transducer  20   c  is mounted on the wall of the wellbore  10  between the devices  12   c  and  12   d . The transducers  20   a - 20   c  can be in the form of conventional electromechanical transducers, or converters, such as tuning forks, cantilevers, oval-mode tools, magnetostrictive drivers, or piezoelectric transducers. It is understood that each transducer  20   a - 20   c  is electrically connected to one of the drivers  16   a  or  16   b  so that it can be driven by the electrical power output from the driver to cause the transducer to vibrate accordingly.  
         [0012]     The transducers  20   a - 20   c  are designed to operate at a desired, predetermined frequency, and preferably at their resonate frequency. For example, one or more of the transducers  20   a - 20   c  can be designed to operate at a relatively high resonate frequency; while the other transducer(s) can operate at a relatively low resonate frequency. As a non-limitative example, if the desired frequency is above 4 kHz, the transducers  20   a  and  20   b  can be in the form of piezoelectric transducers, such as those marketed under the designation PZT-4 by the Edo Corporation of Salt Lake City, Utah. In this case, the transducers  20   a  and  20   b  are connected to the driver  16   a  and the frequency, or frequencies, of the output of the driver  16   a  is matched to the resonate frequencies of the transducers  20   a  and  20   b  so that they are driven at their resonate frequencies. If it is desired to operate below 4 kHz, the transducers  20   c  and  20   d  can be in the form of conventional magnetostrictive drivers that are connected to the driver  16   b , in which case the frequency, or frequencies, of the output of the driver  16   b  is matched to the resonate frequencies of the transducers  20   c  and  20   d  so that they are also driven at their resonate frequencies.  
         [0013]     The transducers  20   a - 20   c  are mechanically coupled to the devices  12   a - 12   d  in a manner so that vibrations of the transducers  20   a - 20   c  are imparted to the devices  12   a - 12   d . The coupling is such that the devices  12   a  and  12   b  provide equal and opposite loads on the transducer  20   a , so that it can be used to vibrate the devices  12   a  and  12   b  simultaneously. Similarly, the devices  12   b  and  12   c  provide equal and opposite loads on the transducer  20   b  so that it can be used to vibrate the devices  12   b  and  12   c  simultaneously; and the devices  12   c  and  12   d  provide equal and opposite loads on the transducer  20   c  so that it can be used to vibrate the devices  12   c  and  12   d  simultaneously.  
         [0014]     A sensor  22   a  is mounted to the outer surface of the device  12   b  and a sensor  22   b  is mounted between the outer surfaces of the devices  12   c  and  12   d . Also, two axially spaced sensors  22   c  and  22   d  are mounted to the inner surfaces of the devices  12   a  and  12   c , respectively. The sensors  22   a  and  22   b  are adapted to sense pertinent downhole data, such as pressure and temperature, outside the devices  12   a - 12   d , and the sensors  22   c  and  22   d  are adapted to sense the same data inside the devices.  
         [0015]     A control unit  24 , which can include, or be in the form of, a microprocessor, or the like, is mounted to the upper end of the device  12   a . Although not shown in the drawings in the interest of clarity, it is understood that the control unit  24  is electrically connected to the sensors  22   a - 22   d  so that the data sensed by the sensors  22   a - 22   d  is transferred to the control unit  24 . The control unit  24  is adapted to process signals from the sensors  22   a - 22   d  and generate corresponding output signals. The drivers  16   a  and  16   b  are also connected to the control unit  24  so that the control unit  24  can provide a signal to the drivers  16   a  and  16   b  to enable them to drive the transducers  20   a - 20   c.    
         [0016]     A telemetry device  26  is mounted on the upper end of the control unit  24 . The telemetry device  26  is electrically connected to the control unit  24  and, as such, is adapted to collect the data from the control unit  24  and transmit the data to the ground surface. Since the telemetry device  26  is conventional, it will not be described in detail.  
         [0017]     It is understood that the devices  12   a - 12   d , the drivers  16   a  and  16   b , the transducers  20   a - 20   c , the sensors  22   a - 22   d , the control unit  24 , and the telemetry device  26  can be assembled as a single unitary package before being inserted in the wellbore  10  in a conventional manner.  
         [0018]     A cable assembly  28 , shown by a dashed line, extends from the ground surface to the telemetry device  26  and to the control unit  24 . It is understood that the cable assembly  28  includes electrical conductors for supplying electrical power from the ground surface. Although not shown in the drawings in the interest of clarity, it is also understood that the cable assembly  28  extends to drivers  16   a  and  16   b  and the sensors  22   a - 22   d  to also power these units.  
         [0019]     In operation, the package consisting of the devices  12   a - 12   d , the drivers  16   a  and  16   b , the transducers  20   a - 20   c , the sensors  22   a - 22   d , the control unit  24  and the telemetry device  26  is inserted in, and mounted to, the wellbore  10  adjacent the formation F as shown in  FIG. 1 . The devices  12   a - 12   d  are packed with sand, or the like, to form gravel packs and production is started. Fluids recovered from the formation F pass through the gravel packs and the devices  12   a - 12   d  and upwardly in the wellbore  10  to the above-mentioned production tubing (not shown) for passing to the ground surface, while the devices  12   a - 12   d  prevent fines or sand from the fluids from passing with the fluids.  
         [0020]     The sensors  22   a  and  22   b  sense the pertinent downhole data, such as pressure and temperature, outside the devices  12   a - 12   d , and the sensors  22   c  and  22   d  sense this data inside the devices  12   a - 12   d . Each sensor  22   a - 22   d  generates corresponding signals that are transmitted to the control unit  24 . The control unit  24  processes and analyzes the above signals and is programmed to respond when the fluid pressure outside the devices  12   a - 12   d  exceeds the fluid pressure inside the devices  12   a - 12   d  by a predetermined amount, indicating that the devices  12   a - 12   d  are at least partially clogged with scale. When this happens, the control unit  24  sends a corresponding signal to the drivers  16   a  and  16   b  to activate them.  
         [0021]     The power output from the drivers  16   a  and  16   b  drive their corresponding transducers  20   a - 20   c  to cause corresponding vibration of the transducers  20   a - 20   c  and therefore the devices  12   a - 12   d  at their resonate frequency in the manner discussed above. These vibrations fracture, or break up, the scale accumulating on the devices  12   a - 12   d . The scale and/or materials recovered from the devices  12   a - 12   d  are allowed to fall to the bottom of the wellbore  10 , or could be circulated, in any conventional manner, to the ground surface for recovery. In the meantime, the downhole data from the control unit  24  is transmitted to the telemetry device  26  which, in turn, transmits it to the ground surface for monitoring and/or processing.  
         [0022]     The output from the transducers  20   a - 20   c  can be in a frequency range that also stimulates the formation F adjacent the devices  12   a - 12   d  and reduces the “skin” around the wellbore  10  that can slow the flow of production fluid from the formation to the wellbore.  
         [0023]     As a result of all of the foregoing, scale accumulating on the devices  12   a - 12   d  is broken up without causing any physical or chemical damage to the devices  12   a - 12   d , while the formation F is stimulated and the skin around the wellbore  10  is reduced.  
         [0024]     The above operation can be terminated after a predetermined amount of time or after the control unit  24  ceases sending the above signal to the drivers  16   a - 16   b  in response to data received from the sensors  22   a  and  22   b  indicating sufficient scale has been removed from the devices  12   a - 12   d.    
         [0025]     According to another embodiment of the invention as shown in  FIG. 2 , the sensors  22   a - 22   d  are eliminated and a reservoir model can be utilized to provide information relating to the need to vibrate the devices  12   a - 12   d  in the above manner. Otherwise the embodiment of  FIG. 2  contains the same components as the embodiment of  FIG. 1 . According to the embodiment of  FIG. 2 , data is initially collected to generate an initial reservoir model that is inputted to the control unit  24 . After production of fluid from the formation F is initiated, the production information is generated and inputted to the control unit  24  which matches the information to the initial model and adjusts the model as necessary to set a working model. As production continues, the additional production data is collected and inputted to the control unit  24  which compares the data to the working model. If there is a match, the data is fed back to the control unit  24  for further processing; and, if there is no match, the drivers  16   a  and  16   b  are actuated to drive the transducers  20   a - 20   c  in the manner discussed above and thus initiate the vibration/production stimulation cycle described above.  
         [0026]      FIG. 3  is a graph of the simulated production from the wellbore  10  vs. time and shows the reservoir model of  FIG. 2  by the rectangular data points, and a deviation from the model by the triangular data points, both before and after the scale is removed from the devices  12   a - 12   d  and the formation F is stimulated, including removal of the skin, in accordance with the foregoing method which can bring the production back to the model values.  
         [0027]     Thus, the system and method according to the above embodiments performs the screening and stimulation functions yet eliminates the problems discussed above. Moreover, the above sensing, analysis, and treatment can be done simultaneously in real time.  
         [0028]     Several variations may be made in both of the above embodiments without departing from the scope of the invention. These variations are as follows:  
         [0029]     1. The control unit  24  can be programmed to adjust the pressure differential required to actuate the drivers  16   a  and  16   b.    
         [0030]     2. The number, type, and location of the screening devices  12   a - 12   d , the drivers  16   a  and  16   b , the transducers  20   a - 20   c , and/or the sensors  22   a - 22   d  can be varied.  
         [0031]     3. The sensors  22   a  and  22   b  could be eliminated and a scale sensor, or detector, could be mounted on each device  12   a - 12   d  to directly detect the presence of scale, and any other foreign materials, and generate a corresponding output signal that is transmitted to the control unit  24  for processing in the above manner.  
         [0032]     4. The control unit  24  can be in the form of any type of data processing device.  
         [0033]     5. The above connections between the control unit  24 , the drivers  16   a  and  16   b , and the sensors  22   a - 22   d , the connections between the drivers  16   a  and  16   b  and the transducers  20   a - 20   c , and the connection between the telemetry device  26  and the ground surface could be wireless.  
         [0034]     6. The cable assembly  28  could be eliminated and a battery pack, or the like, could be provided downhole to supply electrical power to the various units.  
         [0035]     7. Rather than use the reservoir model discussed in connection with  FIG. 2  instead of the sensors  22   a  and  22   b , the reservoir model could be used in addition to the sensors  22   a - 22   b.    
         [0036]     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.