Abstract:
In a production system for producing oil or gas from a well, the production system including a plunger in well tubing, and a motor valve in a sales line connected to a plunger lubricator which connects to the well tubing, a differential pressure controller system includes: a) a plunger arrival sensor; b) a plunger cycle controller receptive to signals from the plunger arrival sensor and receptive to signals from pressure transducers, for controlling the cycle of the plunger; c) a differential pressure controller; d) a first pressure transducer conductively coupled to the differential pressure controller, for measuring pressure in the well tubing, e) a second pressure transducer conductively coupled to the differential pressure controller for measuring pressure in the sales line; and f) a solenoid valve conductively coupled to the differential pressure controller and connected to the motor valve.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application claims the benefit of the following U.S. Provisional Applications:  
         [0002]    No. 60/353,655, filed Feb. 1, 2002;  
         [0003]    No. 60/362,725, filed Mar. 8, 2002;  
         [0004]    No. 60/369,387, filed Apr. 2, 2002; and  
         [0005]    No. 60/406,128, filed Aug. 27, 2002. 
     
    
     
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
         [0006]    Not Applicable.  
         REFERENCE TO A “SEQUENTIAL LISTING,” A TABLE, OR A COMPUTER PROGRAM LISTING APPENDIX SUBMITTED ON A COMPACT DISC  
         [0007]    Not Applicable.  
         BACKGROUND OF THE INVENTION  
         [0008]    1. Field of the Invention  
           [0009]    The present invention relates to control of oil or gas well production in the latter stages of well life and, more particularly, to a differential pressure controller and method for controlling the action of a plunger lift system or oil lift systems, generally known as artificial lift systems.  
           [0010]    2. Description of Related Art  
           [0011]    Artificial lift systems use a plunger lift in combination with a motor valve to take oil or gas in a tubing of a well, and put it in a sales line. When the motor valve is closed, a differential pressure is created across the valve. This pressure is generated as a combination of the rate at which product (gas) is removed from the downstream (sales or line pressure) line and the rate at which pressure builds up on the upstream (tubing pressure) side of the valve. The line pressure is dependent on several factors including the number and pressure of adjoining gas wells and the type and efficiency of the sales line gas compressor. The tubing pressure is dependent on well bore geometry, well depth, rate of fluid influx, the rate of bottom hole pressure recovery and other factors. A person skilled in the art of artificial lift systems will understand the normal cycling of a plunger in a plunger lift system. In this context, the desired recovery time of a well is the same as the plunger fall time, which is a fixed set point chosen by the user.  
           [0012]    The present state of the art for electromechanical control systems in the oil and gas recovery industry can be seen in U.S. Pat. Nos. 5,427,504 (plunger only), 4,921,048, 4,685,522, 4,664,602, 4,633,954 and 4,526,228. The disclosures of these patents are incorporated into this specification by this reference. These systems suffer from open loop problems that manifest themselves as an inability to compensate for the effects of changes associated with 1) varying well production rates, 2) wear of the lift system components, 3) fluid production, and 4) sales line pressure fluctuations. What is needed is a system that resolves these problems by a single electromechanical control device, when an artificial lift system, such as a plunger lift system, is in use.  
         BRIEF SUMMARY OF THE INVENTION  
         [0013]    In a production system for producing oil or gas from a well, the production system including a plunger in well tubing, and a motor valve in a sales line connected to the well tubing, a differential pressure controller system comprises: a) a plunger arrival sensor; b) a plunger cycle controller receptive to signals from the plunger arrival sensor and receptive to signals from pressure transducers, for controlling the cycle of the plunger; c) a differential pressure controller; d) a first pressure transducer conductively coupled to the differential pressure controller, for measuring pressure in the well tubing, e) a second pressure transducer conductively coupled to the differential pressure controller for measuring pressure in the sales line; and f) a solenoid valve conductively coupled to the differential pressure controller and connected to the motor valve. In an alternate embodiment, a single differential pressure transducer replaces the first and second pressure transducers.  
           [0014]    In a production system for producing oil or gas from a well, the production system including a plunger in well tubing, and a motor valve in a sales line connected to the well tubing, a method for efficiently producing oil or gas comprises the steps of: a) opening and closing the motor valve in the sales line in response to differential pressure measured between the well tubing and the sales line; and b) adjusting the timing and rate of the cycling of the plunger.  
           [0015]    In another feature of the present invention, the step of opening and closing the motor valve further includes the steps of: a) measuring the time from when the motor valve opens until the time when a plunger arrival sensor is tripped, to create a plunger travel time; and b) using the plunger travel time to adjust a differential pressure set point for opening and closing the motor valve.  
           [0016]    In another feature of the present invention, the method further includes the steps of: a) measuring the time from when the motor valve closes until the time when the differential pressure set point is met, to create a recovery time of the well; and b) using the recovery time of the well to proportionately adjust the time that the motor valve remains open after the plunger arrival sensor is tripped.  
           [0017]    The present invention offers the advantage of optimal rates for removal of fluid from the well, and thus optimal well production, without intervention of a human operator. In addition, the present invention improves field production rates, because it is sensitive to changes in the sales line pressure and in the well tubing pressure.  
           [0018]    Other features and advantages of the invention will be apparent from a review of the following detailed description of the invention. 
       
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0019]    [0019]FIG. 1 a  is a schematic diagram of the differential pressure controller system of the present invention, illustrated connected to a plunger in well tubing, and connected to a motor valve in a sales line connected to the well tubing.  
         [0020]    [0020]FIG. 1 b  is a schematic diagram of another embodiment of the differential pressure controller system of the present invention, illustrated connected to a plunger in well tubing, and connected to a motor valve in a sales line connected to the well tubing.  
         [0021]    [0021]FIG. 2 is a functional block diagram of the differential pressure controller of the system of the present invention.  
         [0022]    [0022]FIG. 3 is a diagram illustrating the operation of two control loops within the firmware contained in the differential pressure controller.  
         [0023]    [0023]FIG. 4 a , FIG. 4 b , and FIG. 4 c  together constitute a flow diagram illustrating the operation of the control system contained within the firmware of the differential pressure controller. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0024]    In FIG. 1 a , a differential pressure controller system  100  in accordance with the present invention includes a differential pressure controller  102 , a solar panel  104 , and a plunger arrival sensor  110 . The differential pressure controller  102  includes a tubing pressure transducer  106  with its connecting tubing  107 , and a line pressure transducer  108  with its connecting tubing  109 . Well tubing  111  connects to a plunger lubricator  105  which connects to an input of a motor valve  112 , which has its output connected to a sales line  113 . The tubing  107  connects to the plunger lubricator  105 , which has the same pressure as the pressure in the well tubing  111 . The tubing  109  connects to the sales line  113 . The plunger arrival sensor  110  senses the arrival of a plunger  114  in the plunger lubricator  105 . In the preferred embodiment, the plunger  114  is Model No. Super Seal D2, manufactured by Scientific MicroSystems, Inc., located in Tomball, Tex. According to standard practice, the well tubing  111  is inside of a well casing  115 . FIG. 1 b  shows an alternate embodiment that replaces the two pressure transducers  106  and  108  with one differential transducer  116 . Although not shown in the drawings, check valves are sometimes inserted between the motor valve  112  and the points where the tubing  107  and  109  connect.  
         [0025]    Although it does not form part of the invention, the motor valve  112  is preferably a Kimray 2200 series Motor Valve or a Denver Norris Motor Valve. The pressure transducers  106  and  108  are Model No. MSI MSP-400-01K, manufactured by Measurement Specialists Inc, located in Newark, N.J. In an alternate embodiment, the pressure transducers  106  and  108  are Model No. T-1000-AWG-24G, manufactured by WASCO, located in Santa Maria, Calif.. The plunger arrival sensor  110  is Model No. PS-4, manufactured by Tech Tool, located in Millersburg, Ohio. In an alternate embodiment, the plunger arrival sensor  110  is Model No. Trip Mate, manufactured by OKC, located in Longmont, Colo. The solar panel  104  is Model No. MSX-01, manufactured by BP Solar, located in Linthicum, Md.  
         [0026]    Referring now to FIG. 2, the differential pressure controller  102  includes a micro controller  200 , a digital signal conditioning and protection circuit  202 , an analog signal conditioning and protection circuit  204 , a transducer power switching circuit  206 , an LCD power switching circuit  208 , a keypad  210 , an LCD display  212 , a battery  214 , a solar panel  104 , and a regulator  218  and a conditioning circuit  220  for the battery  214  and the solar panel  104 . The micro controller  200  contains a flash memory  200   a , a digital input/output circuit  200   b , and an analog-to-digital converter  200   c.    
         [0027]    In the preferred embodiment, the micro controller  200  is a Model No. 68HC908, manufactured by Motorola, located in Phoenix, Ariz. (or a Model No. Z86E34112, manufactured by Zilog, located in San Jose, Calif.), the keypad  210  is a Model No. MGR STORM 700 series 4X4, manufactured by MGR Industries Inc., located in Fort Collins, Colo., and the LCD display  212  is a dot matrix 2 line by 20 character liquid crystal display, Model No. DMC-50218, manufactured by Optrex, located in Plymouth, Mich.. The keypad  210  enables the user to enter and retrieve parameters and set points from the differential pressure controller  102 . A person skilled in the art of implementing remote terminal unit (RTU) user interfaces could easily create a similar user interface to allow for the configuration and setup of a similar device.  
         [0028]    The plunger arrival sensor  110 , a battery monitor circuit  222 , a high level kill switch  224 , and a low level kill switch  226  generate digital inputs to the digital signal conditioning and protection circuit  202 , which in turn generates digital inputs to the micro controller  200 . The high and low level kill switches  224  and  226  generate inputs that indicate fault conditions in external equipment, and are distinct from the internal high and low pressure kill levels. The tubing pressure transducer  106  and the line pressure transducer  108  generate analog input signals to the analog signal conditioning and protection circuit  204 , which in turn generates analog input signals to the analog-to-digital converter  200   c . The tubing pressure transducer  106  and the line pressure transducer  108  can be powered down using the transducer power switching circuit  206 . The LCD display  212  can be powered down using the LCD power switching circuit  208 .  
         [0029]    The flash memory  200   a  contains programmed instructions, which are collectively known as the firmware  200   d . The micro controller  200  and its firmware  200   d  cause a solenoid driver  228  to activate, causing a latching solenoid  230  to energize or de-energize, depending on activation state. Latching solenoid  230  activation causes the pneumatically driven motor valve  112  to be opened. Latching solenoid  230  deactivation causes the motor valve  112  to close. The firmware  200   d  also allows for the collection of analog pressure data, the detection of digital levels, and the control of digital outputs, in order to effect the functionality illustrated in FIG. 3 and FIG. 4.  
         [0030]    Referring now to FIG. 3, the firmware  200   d  implements two control loops in order to compensate for the lag and dead time effects which are caused by external changes, such as, but not limited to, plunger wear, bottom hole gas pressure, fluid inflow rates, and pressure fluctuations in the sales line  113 . The two control loops are a sales time adjust algorithm  300  and a differential pressure limit adjust algorithm  302 . The output of each affects one of the inputs of the other. These algorithms are self-adjusting within user-defined limits. In the preferred embodiment, the operator uses both of the algorithms, but the user can choose to run one or the other separately.  
         [0031]    The sales time adjust algorithm  300  and the differential pressure limit adjust algorithm  302  interact with each other by adjusting the sales time state timer and the differential pressure limit set points. The sales time adjust algorithm  300  monitors the well recovery time process variable  304  and looks at the plunger fall time set point  306  in order to adjust the sales time state timer set point  308 . In turn this causes the measured well recovery time to tend towards the plunger fall time set point  306 . Changing the sales time state timer set point  308  indirectly affects the travel time process variable  310  that is monitored by the differential pressure limit adjust algorithm  302 . This in turn changes the differential pressure set point that in turn affects the sales time adjust algorithm  300 . In this manner a closed loop control system is achieved.  
         [0032]    Referring now to FIG. 4, a state machine of the firmware  200   d  illustrates a closed-loop control operation by the firmware  200   d , which operates on any well that uses an artificial lift system. The state machine has four operating states: an on time state  400 , a sales time state  402  (also known as the after-flow state), plunger fall time state  404 , and an off-time state  406 . In addition, there are two controlling algorithms, the sales time adjust algorithm  300 , and the differential pressure limit adjust algorithm  302 . Each state has an associated timer. These states contain countdown timers with the exception of the off time state  406 , which has an off time state count-up timer  406   a . The timer values are set using user interface commands, with the exception of the off time state count-up timer  406   a , which cannot be set. As time expires in a state, the differential pressure controller firmware  200   d  will move on to the next state, depending on its configuration and certain external events. The exception is the off time state  406 . The firmware  200   d  will stay in the off time state  406  until the differential set point is met.  
         [0033]    At the power up step  408 , the differential pressure controller  102  defaults to the plunger fall time state  404  to ensure that the motor valve  112  is closed.  
         [0034]    The on time state  400  is the state of the differential pressure controller  102  that opens the motor valve  112  to allow for gas flow through the sales line  113 . As the latching solenoid  230  opens the motor valve  112 , an on time state timer  400   a  begins to count downward from the initialized setting, towards zero time. If the on time state timer  400   a  expires, the controller will move to the plunger fall time state  404 , bypassing the sales time state  402 . Before the firmware  200   d  changes state to the plunger fall time state  404  the firmware  200   d  adds the maximum differential pressure value to the differential pressure set point  303 , as indicated by block  403 . Under normal configuration settings, on time state  400  can be interrupted by a plunger detector arrival signal, as indicated by the plunger arrival decision block  400   b , which will move the differential pressure controller firmware  200   d  to the sales time state  402 . Before the firmware  200   d  moves to the sales time state  402  it calculates the plunger travel time  306  and the differential pressure set point  303 . The on time state  400  can also be interrupted by the pressure kill algorithm  410  as a result of the high pressure kill level step  410   b  or the low pressure kill level step  410   a . Each of these levels is measured from the line pressure transducer  108 . When a level of pressure in the sales line  113  exceeds a user-entered set point, the pressure kill algorithm  410  begins. The pressure kill algorithm  410  either waits for the pressure level to revert to the normal state, or if the differential pressure controller  102  is not in the plunger fall time state  404 , the pressure kill algorithm  410  forces the state machine into the plunger fall time state  404 .  
         [0035]    The sales time state  402  starts when a plunger detector arrival signal is detected during the on time state  400 . During the sales time state  402  the motor valve remains open. When the timer associated with this state expires, the firmware  200   d  will move to the plunger fall time state  404 .  
         [0036]    The sales time adjust algorithm  302  automatically adjusts the sales time state timer.  
         [0037]    The plunger fall time state  404  closes the motor valve. This state cannot be interrupted by external events. The plunger fall time state  404  can be entered if the sales time state  402  timer expires or if the pressure kill algorithm  410  is tripped. The plunger fall time state  404  time is the time allotted for the plunger  114  to return to the bottom of the well tubing. After the plunger fall time state  404  timer has expired, the off time state  406  is started, unless either the high or low kill levels are exceeded. If either the high or low kill levels are exceeded, the firmware  200   d  waits until the pressure is within the limits set by the user.  
         [0038]    The off time state  406  checks the differential pressure value against the differential pressure set point  303  that is adjusted by the differential pressure limit adjust algorithm  302  as indicated by block  406   b . If the differential pressure is below the differential pressure set point  303 , then the motor valve  112  remains closed. If the differential pressure is above, or moves above the differential pressure set point  303 , the differential pressure controller  102  opens the motor valve  112 , and the firmware  200   d  moves to the on time state  400 . Before moving to the on time state  400  the firmware  200   d  calculates the well recovery time process variable  304  as indicated by block  412 . The off time state can be interrupted by the pressure kill algorithm  410 , which will send the firmware  200   d  to the plunger fall time state  404 . The differential limit set point being reached completes the off time state  406 . The timer associated with the off time state  406  counts-up, indicating how long the well has been off past the end of the plunger fall time state  404  as indicated by block  406   a.    
         [0039]    The differential pressure limit adjust algorithm  302  may be explained in the following way. Referring to Fig la, the differential pressure is the pressure difference between the pressure indicated by the tubing pressure transducer  106 , and the line pressure indicated by the line pressure transducer  108 .  
         [0040]    The differential pressure controller  102  adjusts the differential pressure limit based on the difference in the actual plunger  114  travel time and the user-entered travel time. The user will enter the desired plunger  114  travel time, and the differential pressure controller  102  will adjust the differential pressure set point in order to keep the plunger  114  travel time at the desired time. For example, if the plunger  114  travel time is too fast, then the differential pressure controller  102  will decrease the differential pressure set point. The opposite is also true. If the plunger  114  travel time is too slow, then the differential pressure controller  102  will increase the differential pressure set point. The increase and decrease in the pressure limit is based on a percentage of the error in the measured plunger  114  travel time and desired plunger travel time as indicated by the plunger travel time set point.  
         [0041]    Additional control is achieved by using a minimum differential pressure set point. Referring again to FIG. 3, the minimum differential set point prevents the sales time adjust algorithm  300  from adding sales time until the minimum differential pressure set point value is met. The minimum differential pressure set point does not prevent sales time being subtracted if required by the sales time adjust algorithm  300 .  
         [0042]    A maximum differential set point prevents the differential pressure limit adjust algorithm  302  from adding to the differential pressure set point  303  once the maximum differential set point value is met. This prevents the firmware  200   d  from trying to compensate when the well may have other problems.  
         [0043]    The sales time adjust algorithm  300  may be explained in the following way. A recovery time process variable  304  may be calculated by finding the difference between the start of the fall time state and the time that the pressure differential set point  303  is met in the off time state  406 .  
         [0044]    The sales time state time set point in the firmware  200   d  is adjusted based on the well recovery time process variable  304 .  
         [0045]    Referring again to FIG. 4, the user will input a maximum sales-time adjust value. If the differential pressure is met during the plunger fall time state  404 , then the sales time state  402  timer set point is adjusted proportionately based on the sales-time adjust value. In addition, the motor valve  112  will not be opened (turning ON the well) until the plunger fall time state timer has expired.  
         [0046]    For example: If the differential pressure is met at fifty (50) percent of the plunger fall time state timer set point then fifty (50) percent of the sales-time adjust value is added to the sales time state timer set point. If the differential pressure is met at one hundred and fifty (150) percent of the plunger fall time state timer set point then fifty (50) percent of the sales-time adjust value is subtracted from the sales time state timer set point.  
         [0047]    When the differential pressure set point is reached, during the off time state, the firmware  200   d  will calculate the difference between the actual recovery time and the desired recovery time which is set by the plunger fall time set point. The firmware  200   d  will add or subtract time to the sales time state timer based on a percentage of the error between the desired recovery time and the actual recovery time. If the change in time is to be added to the sales time state timer, the controller waits for a plunger arrival indication, before proceeding with the addition. The maximum error allowed is twice the plunger fall time (target time) value. If this limit is exceeded, then one hundred percent of the sales-time maximum adjust is subtracted from the sales time state timer, and the differential pressure controller  102  restarts the timing. If the differential set point is met at the start of the plunger fall time state and the motor valve  112  is closed, then one hundred percent of the maximum sales time adjust is subtracted from the sales time state timer and the differential pressure controller  102  restarts the timing.  
         [0048]    The user can determine plunger wear and wear rate by monitoring the change in the differential pressure set point.  
         [0049]    Although this detailed description has shown and described illustrative embodiments of the invention, this description contemplates a wide range of modifications, changes, and substitutions. In some instances, one may employ some features of the present invention without a corresponding use of the other features. Accordingly, it is appropriate that readers should construe the appended claims broadly, and in a manner consistent with the scope of the invention.