Abstract:
A data communications system and method for transmitting data over a string between a surface location and a sub-surface location in a well bore in which a load varying device at the sub-surface varies the mechanical load on the string to be indicative of the data and a load measuring apparatus at surface monitors the mechanical load on the string and decodes the data. Data transmission is described from a pump assembly through a sucker rod string. Embodiments of load varying devices using electrical generators, friction rollers and hydraulic and pneumatic brakes are also described.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This is a national stage application under 35 U.S.C. §371(c) of prior filed, copending PCT application serial number PCT/GB2014/051235, filed on Apr. 22, 2014, which claims priority to Great Britain Patent Application Serial No. 1307447.1 filed Apr. 25, 2013 and titled DATA COMMUNICATIONS SYSTEM. The above-listed applications are herein incorporated by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    Embodiments of the invention relate to data transmission to and from down hole equipment and in particular, though not exclusively, to a data communication system and a method of data transmission through a sucker rod string between the sub-surface and a surface location of a well bore. 
         [0003]    In the exploration and production of oil and gas wells, well bores are drilled from the surface to a subsurface location to access the reserves. The well bore is typically ‘cased’ with tubing to prevent collapse. A string can be run into the well bore to position down hole equipment at a sub-surface location. Down hole equipment is understood to refer to any tool, equipment or instrument that is used in a well bore. 
         [0004]    Data needs to be transmitted between down hole equipment and the surface for various reasons. For example, monitoring performance of motors/pumps; transmission of control signals for control of valves; measuring device orientation and position, and making physical measurements. Power may also need to be transmitted to the down hole monitoring equipment. Due to the complexity of construction and the depths which wells are drilled, the data is sent to surface without installing dedicated cables and power for the down hole instrumentation is also sent without adding wires to the well equipment. 
         [0005]    Telemetry systems are known which use the casing to transmit electromagnetic and acoustic data signals from a sub-surface location to a surface location. Such systems typically cannot achieve transmission of power from surface to sub-surface. 
         [0006]    An embodiment of the present invention provides an alternative wireless system and method of data transmission when an electrical cable is not present in the well bore. In an embodiment of the present invention an alternative system and method of power transfer is also described. 
       SUMMARY OF THE INVENTION 
       [0007]    According to a first aspect of the present invention there is provided a data communications system for transmitting data over a string between a surface location and a sub-surface location in a well bore, the data communications system comprising a sub-surface system module including load varying means to vary mechanical load on the string to be indicative of the data and a surface system module including load measuring apparatus to monitor the mechanical load on the string and a processor for determining the data from variation in the load. 
         [0008]    In this way, the data is coupled onto the string by varying the mechanical load on the string using a force modulating device. The variation in mechanical load is applied in a way that can be read as information at the surface. The system therefore provides wireless transmission of data between the surface and sub-surface. 
         [0009]    In an embodiment, the string is a sucker rod string. In this way data can be transmitted from surface driven down hole equipment, such as a PCP, plunger pump, or sucker rod pump system. In this embodiment, the sub surface module alters the mechanical force required to operate the pump in such a way as to convey measured sub surface data, and the surface module measures and decodes this mechanical load change. The effect of the mechanical pumping system on the data signal integrity can be minimised. 
         [0010]    In an embodiment, the load varying means comprises a power generator module which is used to alter the mechanical loading on the string. The load varying means is an electrical generator with a variable electrical load which alters the mechanical loading of the string. The electrical generator may be a linear or rotary electrical generator. Alternatively, the load varying means may comprise a mechanical or hydraulic brake with a control mechanism. The brake may be a linear or rotary roller wheel with variable friction. Alternatively, the brake may be a linear stroking hydraulic piston with variable chokes on the hydraulic fluid feed or outlet which vary the force and thus the mechanical load on the string. Optionally, the brake may be a rotary acting hydraulic piston or motor with variable chokes on the hydraulic fluid feed or outlet which varies the force required to rotate the assembly. 
         [0011]    In an embodiment, the load varying means varies the load in a ‘high-low’ pattern to form bits representative of single bit data. The ‘high-low’ pattern may be an ‘on-off’ pattern. In this way, the data is sent as single bit data. Alternatively, the data may be sent in binary bit strings using NRZ or any other encoding scheme. Where the data is sent in binary bit strings, which may be encoded, the binary bit strings are also configured as PN sequences to improve signal to noise ratio. 
         [0012]    In an embodiment, the load varying means is mounted above a pump assembly being assembled and installed in the same way as the pump assembly. In this way, the sub-surface module can be fitted to any standard pump assembly using sucker rod mechanical drive from surface. 
         [0013]    In an embodiment, the load measuring apparatus comprises a detection system at surface to measure the changes in the mechanical loading created by the sub-surface module. The detection system may be a load cell, pressure sensing device, bending beam, or use the current sense from the pump drive motor. 
         [0014]    In an embodiment, the sub-surface module includes one or more gauges to make down hole measurements. More particularly, the load varying means is used to power at least one electronics module in the one or more gauges. In an embodiment, the one or more gauges have a power module. The power module may derive power from the load generator and store and regulate this power sufficient to run the at least one electronics module in the one or more gauges. Power can thus be maintained on the down hole monitoring instrumentation if the main sucker rod drive has stopped, which provides essential information in the event of pump shut downs or other major events in the well. 
         [0015]    In an embodiment, the load varying means may be directly dependent on temperature or pressure. In this way, the mechanical load on the string is directly affected by pressure or temperature so providing a simple direct method of measuring the down hole environment. 
         [0016]    According to a second aspect of the present invention there is provided a method of transmitting data on a string between a surface location and a sub-surface location in a well bore, comprising altering a mechanical load on the string at the subsurface location, the load being altered to convey data, monitoring the change in mechanical load on the string at the surface and decoding the data. 
         [0017]    In this way, data signals are be transmitted from the sub-surface to the surface via the string. 
         [0018]    In an embodiment, the method includes the step of sending the data as a single bit data stream. Alternatively, the data may be sent in binary bit strings using NRZ or any other encoding scheme. Where the data is sent in binary bit strings, which may be encoded, the binary bit strings are also configured as PN sequences to improve signal to noise ratio. 
         [0019]    In this way, data signals can be transmitted from the sub-surface to the surface through the string via a wireless alternating load transmitter. 
         [0020]    In an embodiment, the data is transmitted over a sucker rod string in a mechanical pump drive. The method includes the step of applying a change in the mechanical load during a selected part of the pump cycle. In this way, the time period where the load changes are applied is easier to detect. 
         [0021]    The selected part of the pump cycle is when the load from the pump drive action is steady. In this way, changes to the mechanical load can be more easily seen. The selected part of the pump cycle is when the load on the sucker rod string is lowest. In this way, the changes will appear larger as compared to the background loads. 
         [0022]    The method includes the step of varying the load during the down stroke on a sucker rod pump. This will improve the signal to noise ratio. 
         [0023]    Optionally, the method includes the step of varying the load during the upstroke. In this way, rod string buckling is prevented. 
         [0024]    The method includes the step of varying the load at a relatively high frequency. In this way, the data signal transmission can be differentiated more readily from background pump noise. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0025]    The present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: 
           [0026]      FIG. 1  shows a typical set up of down hole equipment in a well, in the form of a rod pump completion; 
           [0027]      FIG. 2  shows a schematic block diagram of a data communication system according to a first embodiment of the present invention; 
           [0028]      FIG. 3  shows an illustration of a down hole pump assembly including a data transmission system according to an embodiment of the present invention; 
           [0029]      FIGS. 4(   a ) and  4 ( b ) are graphs illustrating a transmitted binary signal in the form of a ‘1’,  FIG. 4(   a ), and a ‘0’,  FIG. 4(   b ), according to an embodiment of the present invention; 
           [0030]      FIGS. 5(   a )-( c ) illustrate data transmission systems, with  FIG. 5(   a ) being the data transmission system of  FIG. 3 ;  FIG. 5(   b ) being a further embodiment of a data transmission system; and  FIG. 3(   c ) being a yet further embodiment of a data transmission system; and 
           [0031]      FIGS. 6(   a ) and  6 ( b ) show configurations of data transmission systems to provide fluid flow in a well bore according to embodiments of the present invention 
       
    
    
     DETAILED DESCRIPTION 
       [0032]    Reference is initially made to  FIG. 1  of the drawings which illustrates a data transmission system, generally indicated by reference numeral  10 , located within a well  12 , to transmit data from a sub-surface location  14  to a surface location  16  through a string  18  located in the well  12 , according to an embodiment of the present invention. 
         [0033]    Well  12  is a typical oil, gas or water well in which a well bore  20  is drilled and lined with casing  22  held in place by cement  24 . Tubing  26  is inserted in the casing  22 , providing an annulus  28  therebetween. Oil  30  from an oil bearing zone or reservoir  32  in the sub-surface  14 , enters the tubing  26  through perforations  34  in the casing, to travel to the surface  12 . When the reservoir pressure is insufficient to lift the oil  30  to the surface  16 , it is common to provide down hole equipment in the form of an artificial lift system. Types of artificial lift systems include hydraulic pumps, Rod pumps, Electric Submersible Pumps (ESPs), Jet Pumps, Progressing-Cavity pumps (PCPs) and gas lift.  FIG. 1  of the drawings illustrates a typical rod pump completion  36  in a well bore  20 . 
         [0034]    The completion  36  consists of a down hole pump assembly  38  in the oil producing section of the reservoir  32 . This pump  38  is deployed on a tubing string  26  and driven mechanically by a sucker rod string  18 . A rod pump completion  36  provides a reciprocating pump  38  driven from the surface  16  by drive units which move a polished rod  18  through a stuffing box  40 . A main walking beam  42  is pivotally mounted on a Samson post  44  with one end providing a horse head  46  with a bridle  48  attached to the polished rod  18 . The opposing end is connected to a pitman arm  50  and crank  52  which are coupled to a motor drive and gearbox assembly  54  to reciprocate the walking beam  42 . 
         [0035]    On reciprocation of the walking beam  42 , the rod string  18  is stroked up and down through the stuffing box  40 . At the end of the rod  18 , arranged at the perforations  34 , is a pump barrel  56  including a standing valve  58  and a travelling valve  60  connected to the end of the rod  18 . Each stroke lifts the oil into the tubing  26 . At the surface  16 , the lifted oil and gas can be siphoned off via a gas line  62  and an oil line  64  from a tee  66 . 
         [0036]    While a rod pump completion  36  can be considered as relatively simple technology, they are expensive to maintain and repair. Consequently, monitoring is required in order to ensure correct operation and, most importantly, avoid a pump off condition. This occurs when an insufficient amount of fluid enters the pump barrel  56  on a downstoke. On the next downstroke, the travelling valve  60  and rod  18  impact the fluid in the pump barrel  56 , sending shock waves through the assembly  38  causing damage. Additionally, it is beneficial if the motor and drive unit  54  can be controlled so that the rod  18  reciprocates and drives the pump at maximum efficiency. The majority of current control systems are limited to monitoring the position of the polished rod  18  in the stuffing box  40  to infer conditions at the pump barrel  56 . 
         [0037]    In an embodiment of the present invention, one or more down hole gauges are mounted sub-surface  14  in the vicinity of the pump barrel  56  and the data from these gauges is transmitted to surface  16  via a data transmission system  10 . 
         [0038]    Referring now to  FIG. 2  of the drawings there is illustrated a functional block diagram of a data transmission system  10 . Located sub-surface  14  is a measurement module  68  which measures any required parameter of the pumping system  38 , such as pressures temperatures, vibration and fluid presence. The measurement module  68  is powered by a power regulator module  70 , which also transmits the measured data to a load modulating device  72 , all located sub-surface  14 . There is a mechanical transmission in the form of a string  18 , between sub-surface  14  and surface  16 . The load modulating device  72  acts on the string  18  in response to the data. Located at the surface  16  is a measurement device  74  which senses the variation in the mechanical load on the string  18 . The measurement device  74  may be a load cell, pressure gauge or optical sensing device. A processor  76  decodes the sensed load variations and generates readings of the data measured in the measurement module  68 . There may be an optional display or computer logging system  78  where the information system is presented to an operator and/or stored for future review. 
         [0039]    Reference is now made to  FIG. 3  of the drawings which illustrates the sub-surface components of a data transmission system  10  fitted to a down hole pump assembly  38 . Mounted in the tubing  26  above the down hole pump assembly  38  is a load modulating device  72 . Device  72  has a substantially cylindrical housing  80  with an outer diameter in an embodiment no greater than that of the pump  38 . Within the housing  80  there is arranged a stator  82 . Stator  82  is a cylindrical arrangement of static windings  84  providing a bore  86  therethrough. The stator  82  is attached to the body  80  as described herein after with reference to  FIGS. 6(   a ) and ( b ). Located upon the rod string  18  in the vicinity of the stator  82  is an actuator  88  in the form of a magnetic core. The magnetic core comprises multiple magnets  132  arranged around and along the rod  18 . A down hole electronics module  90  is also arranged on the tubing  26  between the load modulating device  72  and the down hole pump assembly  38 . The tubing  26  has a narrower diameter in this region to accommodate the down hole electronics module  90  in a manner as is known in the art. The down hole electronics module  90  contains the measurement module  68  and the power regulator module  70 . 
         [0040]    In use, device  72  and the electronics module  90  are arranged on the tubing  26  when the tubing  26  is run in the well bore  20  to locate the down hole pump assembly  38  at the reservoir  32 . The actuator  88  is located in the sucker rod string  18 . With the data transmission system  10  in place, the pump assembly  38  can be operated as normal. When measurements are required, the measurement module  68  operates gauges and/or other sensors to record the desired parameters such as temperature, pressure, vibration and fluid presence. Recorded data is transferred into bits and the signal transmitted to the power regulator module  70 . The power regulating module  70  then controls the load modulating device  72  to vary the force between the stator  82  and actuator  88  such that the mechanical load on the rod  18  varies in response to the data signal. Thus an increase in load may signify a bit equal to ‘one’ and a decrease in load may signify a bit equal to ‘zero’. At the surface  16 , the measurement device  74  will monitor the change in load and the processor  76  will decode the load variations and reconstruct the data signal from the measurement module  68 . Data signals from different gauges may be sent in series by this method. 
         [0041]    This provides transmission of a single bit data stream. However, the data may be sent in binary bit strings using NRZ or any other encoding scheme. Also, where the data is sent in binary bit strings, which may be encoded, the binary bit strings may also be configured as PN sequences to improve the signal to noise ratio. 
         [0042]    The electronics module  90  may monitor the pump cycle and transmit the data at a selected part of the pump cycle so that the time period where the load changes are applied is easier to detect at the surface  16 . Choosing the selected part of the pump cycle to be when the load from the pump drive action is steady will give changes to the mechanical load which can be more easily seen. Taking the selected part of the pump cycle when the load on the sucker rod string is lowest ensures that the changes will appear larger as compared to the background loads. Transmitting data by varying the load during the down stroke on a sucker rod pump will improve the signal to noise ratio. Conversely, transmitting data by varying the load during the upstroke will prevent rod string buckling. 
         [0043]    Additionally, if the load is varied at a relatively high frequency compared to the stroke frequency, the data signal transmission can be differentiated more readily from background pump noise. 
         [0044]    Reference is now made to  FIGS. 4(   a ) and ( b ) which illustrate the data decoding from the load measurement. In  FIG. 4(   a ), the force or load  92  on the string  18  is measured against time on the stroke  94 . The trace  96  shows an increase  90 , which begins at a selected time in the pump cycle, is held for a period of time  100 , before decreasing  102  back to its starting level  104 . This can be considered as transmission of a ‘one’ in binary code. Similarly the inverse can be performed to provide transmission of a binary sequence. In  FIG. 4(   b ), transmission of a ‘zero’ can be achieved by decreasing  106  the load at a preselected time in the cycle period, for a period of time  108 , before increasing  110  back to its starting level  112 . Clearly depending on the physical size of the pumping system and the depth it may be possible to send more than one bit of information per pump stroke, so the data speed can be anywhere from a single bit as illustrated to many bytes per pump stroke. 
         [0045]    It is also realised that in passing the actuator  88  through the bore  86  of the stator  82 , the effect of passing a magnetic field through a set of electromagnetic windings  84  can generate an electric current. This current is transmitted to the power regulator module  72  where it can be stored and used to power the gauges and sensors in the measurement module  68 . With the ability to store power down hole, the measurement gauges and sensors can operate when the pump when the main sucker rod drive  54  has stopped which provides essential information in the event of pump shut downs or other major well events. 
         [0046]    Referring now to  FIGS. 5(   a ) to ( c ), there is shown embodiments of load varying devices. Those skilled in the art will recognise that these do not form an exhaustive list but are merely illustrative of the types of devices available.  FIG. 5(   a ) shows a load varying device, generally indicated by reference numeral  114 , being an electromagnetic linear generator according to the embodiment of a data transmission system as presented and described with reference to  FIG. 3 . Actuator  88  provides a magnetic core on the rod  18  which is stroked within a static electromagnetic winding  84  allowing power to be drawn from the load varying device  114 . Also, by altering the electrical loading, the force required to operate the pump (not shown) can be altered. 
         [0047]      FIG. 5(   b ) shows a load varying device, generally indicated by reference numeral  116 , based on a mechanical brake according to the embodiment of a data transmission system. Body  80  has the same outer diameter as the device  114 . On an inner surface  118  of the body  80 , there are arranged roller contacts  120 . The roller contacts  120  are arranged to make frictional contact with the rod  18  as it passes through the body  80 . The body  80  can be considered as a central bearing tube with a mechanism for altering the force which the roller contacts  120  apply to the shaft of the rod  18 . Altering the force will vary the load upon the rod  18  which can be decoded at the surface  16 . In this way data is transmitted to the surface  16 . The device  116  can also contain a mechanically driven power generator to allow electrical power to be used for local electronics down hole. 
         [0048]      FIG. 5(   c ) shows a load varying device, generally indicated by reference numeral  122 , based on a hydraulic brake according to the embodiment of a data transmission system. In this device  122 , hydraulic or pneumatic pistons  124  are used to provide a load. The sucker rod  18  is latched onto this system through a mechanical latch  126  allowing the pistons  124  to act directly on the rod string  18 . Thus by varying the pistons  124  position, the load is varied upon the string  18 . If data is coupled onto the pistons  124  by varying their position, this load variation can be read at surface  16  and decoded to derive the data. Power can be generated by using a small linear generator in the same outline as one of the pistons, or by adding a small turbine generator to the hydraulic or pneumatic circuit of one or all of the pistons. 
         [0049]    It will be realised that the load varying devices  114 ,  116 ,  122  require to operate in the tubing  26  without restricting the flow of fluid from the pump assembly  38  which is being lifted to the surface  16 . Thus fluid must be able to flow past each device  114 ,  116 ,  122 . Additionally, a compromise between clearance and wear must be made as while a smaller clearance between the actuator and stator will increase the power transfer, it will also increase the chances of sticking and wear. Referring now to  FIGS. 6(   a ) and ( b ) there are illustrated schematic cross-sectional views through load varying devices according to further embodiments of a data transmission system which achieve the required fluid bypass. 
         [0050]    Referring initially to  FIG. 6(   a ), the outer stator  82  is shown as an annular tube which is static. The actuator  88  provides a moving magnetic or mechanical centre piece  128 . The centre piece  128  has an annular outer wall  130  upon which is arranged the active parts such as magnets  132  or roller contacts  120 . These active parts are designed to occupy a space outside the nominal bore  134  of the production tubing  136 , and inside the static section  82  of the device  114 , 116 , 122 . A central support  138  connects into the rod  18  having support spindles  140  to the outer wall  130 . Spaces  142  between the spindles  140  allow the fluid to flow freely through the centre of the device  114 , 116 , 122  while maintaining a small clearance between the outer wall  130  and the stator  82  for good power transfer. This structure would also allow wiper seals to be used between the stroking part  88  and the static section  82  to assist in preventing debris from getting into the moving surfaces. 
         [0051]    An alternative arrangement is shown in  FIG. 6(   b ). In this Figure the stator  82  remains the same. The central support  138  now has a larger diameter which can accommodate parts of the actuator  88  if required. The active parts are now located in wings  144  located around the edge of the central support  138 . Bypass channels  146  are present between the wings  144  to provide for fluid flow through the device  114 , 116 , 122 . The outer edge  150  of each wing  144  is arranged to be rounded and provide a small clearance with the stator  82  to give good power transfer. 
         [0052]    In a yet further embodiment the load varying device is formed from a material sensitive to temperature or pressure so that the load on the string is directly dependent on temperature or pressure which the device is exposed to. In this way temperature or pressure can be read at the surface without requiring any power generator down hole. 
         [0053]    An embodiment of the present invention provides a system and method of data transfer between sub-surface and a surface location of a well bore using the already present string in the well bore. 
         [0054]    An embodiment of the present invention provides a wireless system and method of data transfer between sub-surface and a surface location in a well bore. 
         [0055]    An embodiment of the present invention provides a wireless system and method of power transfer to down hole equipment in a well bore. 
         [0056]    It will be apparent to those skilled in the art that various modifications may be made to the invention herein described without departing from the scope thereof. For example, other load varying devices may be considered as may the system and method be applied to other instrumentation on a string within a well bore. Additionally, though the string in the present invention has been described as a tubular string, coiled tubing and wireline strings may also be considered.