Patent Publication Number: US-2022228473-A1

Title: Sucker rod pump automated control method and system

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     The present patent application claims priority to Ukrainian patent application a202100216 filed Jan. 20, 2021. 
     FIELD OF INVENTION 
     The claimed invention relates to a field of electrical engineering, generally to control of a sucker rod pump (SRP) for oil and gas wells in particular to methods and systems for automated operation of rod pumps using calculations and analysis of rod pumps operating parameters. 
     BACKGROUND 
     The sucker rod pump installations are technological equipment used for a liquid extraction out of wells characterized by a considerable depth. Due to a design and manufacture simplicity, reliability and high maintainability, this type of equipment has been widely used since the end of the 18th century, and has not lost its relevance to this day. According to statistics, 90% of wells in Western Europe are operated using SRP, in the USA—85%, in Russia—about 53%. 
     One of the main tasks of such equipment operation is adaptation to modern requirements of automation control and the providing methods of a flow rate intelligent optimization. 
     Difficulties in solving such technical task lie in providing automation of measurements of operating parameters its processing and analyzing, with forming control commands. 
     In particular, forming a surface and a down hole dynamometer card. Wherein the dynamometer card displays a polished rod load value of the SRP and the sucker rod pump filling rate are the most important indicators to ensure the automated operation of the equipment. 
     The known methods and systems for measuring the SRP parameters include the polished rod load sensor, the polished rod position sensor, a down hole sensor, an echo meter or a flow sensor. Using of the known methods requires an interruption of the technological process and can only be performed by specialized equipment that requires a high qualification level, which is not always possible to implement in the field in short term. As a result, it may lead to a time losses of the technological process or operation in emergency conditions, which leads to decreasing of wells productivity. 
     Various methods and systems for automated operation of the SRP are known. For example the patent No EA029265B1 disclosing a method and system to determine the position of a sucker rod pumping without a position sensing device during production pumping. A pump control system of the sucker rod pumping system includes a controller coupled to a database, with the controller configured to access an rxless torque value in the database. With the stored rxless torque value representative of toggle points of the crank arm during an initial calibration pumping cycle, the controller further is configured to continuously sample the rxless torque value of the system and determine the crank arm position in relation to the sample rxless torque value. The controller adjusts the pumping system for optimal operations, without a crank arm position sensor during production pumping by identifying a toggle point and setting the crank arm position estimate equal to the value corresponding to the crank position at the identified toggle point. The rod position and load can be used to control the operation of the pump in order to optimize the operation of the pump. In addition, the American Petroleum Institute (API) standards are used to determine the geometry of the pump allowing the use of readily accessible data from pump manufacturers. The plant identification procedure is used to determine the installation-specific parameters specific to a particular pump when calculating the operating parameters used in closed-loop control in real time by the operation of a sucker pump, eliminating the need for creating extensive reference tables used in the calculation of performance. 
     Also, the U.S. Pat. No 7,168,924B2, IPC F04D13/10 disclosing a method of controlling the performance of a rod pump used for transferring fluid within a fluid system. The rod pump includes a rod string carrying a downhole pump, and a variable drive with an electrical drive motor coupled to the rod string for reciprocating the rod string. The known method comprising the steps of:
         measuring electrical voltage applied to the drive motor and electrical current drawn by the drive motor;   using the measured values of electrical voltage applied to the drive motor and current drawn by the drive motor to calculate values of motor torque and motor velocity for the drive motor;   using the values of motor torque and motor velocity to calculate values representing operating parameters for the rod pump;   using one or more of the operating parameter values to produce command signals; and   using the command signals to vary the velocity of the downhole pump to cause the downhole pump to closely follow the polished rod position while limiting tensile and compressive forces excursions in rod load as the rod string is being reciprocated.       

     The disclosed method (U.S. Pat. No. 7,168,924B2) as well as patent U.S. Pat. Nos. 8,444,393B2 are providing nearly instantaneous readings of motor velocity and torque which can be used for both monitoring and real-time, closed-loop control of the rod pump. In addition, U.S. Pat. Nos. 7,168,924B2 and 8,444,393B2 are teaching of usage American Petroleum Institute specification geometry and system identification routines are used to establish parameters used in calculating the performance parameters that are used in real time closed loop control of the operation of the rod pump, obviating the need to create large look-up tables for parameter values used in calculating performance parameters. Simple parameters defining the special geometry used in belt driven pumping units are also included in the control. 
     The disadvantages of the prior art include a high dependence on an accuracy of data related to the SRP geometry, as well as usage of voltage measurement sensors. Such dependences of data related to the SRP geometry may lead to significant errors in the calculation of the polished rod load and velocity values because of fact that most of SRP, due to their long service life, may have changes in geometry in relation to the nonnative data. 
     The technical result achieved by the implementation of the invention comprising an increase measuring accuracy characteristic of the SRP and high-precision control of the variable frequency drive in order to optimize a flow rate in a real time. 
     SUMMARY OF THE INVENTION 
     The disadvantages and limitations of the background art discussed above are overcome by the present invention. With this invention, there is provided a method of a sucker rod pump automated control. The described method comprising steps of measuring the sucker rod pump parameters. Wherein counting the sucker rod pump geometry and forming a dynamometer card of the sucker rod pump parameters. A step of providing the sucker rod pump motor control signals depending on measured parameters, comprising at least a load or/and a velocity of a polished rod. Wherein at least the motor torque, the polished rod load or/and velocity are calculated based on mass and geometry values of the sucker rod pump components with counting current and voltage parameters. A step of calculating the motor momentary power value (MMP) and a counter weight system power (CWP) during each reciprocating stroke of the polished rod. On that step using a variable speed drive (VSD) active power value excluding a losses. Wherein calculating the active power value based on a frequency task value. Also, on the MMP calculation step changing the frequency task value relative to the sucker rod pump filling rate. During the MMP calculation step measuring the angle of the sucker rod pump walking beam, and based on the walking beam angle value, forming the real time values of the sucker rod pump crank angle and the polished rod velocity with using geometry dependences of the sucker rod pump components. 
     According to the possible embodiment of the invention, the method comprising steps of obtaining the motor torque average value by comparing the motor torque average value relative to the motor torque reference value. Wherein taking the motor torque reference value calculated on a first sucker rod pump action, and taking the motor torque reference value calculated on low motor velocity, wherein said motor torque reference value showing a ratio between the motor torque average value and the sucker rod pump filling rate, wherein at least the sucker rod pump filling rate reflects changing of the polished rod load. 
     In one embodiment providing calculation the motor torque average value during each reciprocation period of the polished rod, wherein the reciprocation period start is related to the polished rod end point. 
     Further in accordance with the invention calculating a current motor power expended in motion of the polished rod, forming a current motor power based on the VSD active power value excluding the losses, and calculating a stator and a rotor power loss of the motor. Providing the current motor power calculation taking into account the sucker rod pump dynamic moment and a mechanical loss within the sucker rod pump swing joints. 
     One method for the sucker rod pump using the VSD programmable controller, forming a surface and a down hole dynamometer card of the sucker rod pump parameters. Wherein calculating the motor momentary power value (MMP), the counter weight system power (CWP), the polished rod load or/and velocity. 
     According to the possible embodiment, based on the sucker rod pump parameters dynamometer card forming the frequency task value and calculating the VSD output voltage. 
     In one embodiment calculating geometry dependences of the sucker rod pump components via dimensioning, wherein using the geometry dependences for calculating the counter weight system power (CWP), the polished rod load or/and velocity. 
     Further in accordance with the invention calculating the load zero portion at the polished rod end points, wherein the load zero portion is forming a part of the polished road stroke length. Wherein forming the polished rod load constant value at an input/output of the zero portion, and forming an intermediate load value as a calculated mathematic value. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1 —is a sucker rod pump structure; 
         FIG. 2 —is an automated control system of the sucker rod pump structure; 
         FIG. 3 —is a method of forming constructing dynamometer card (Stage 1); 
         FIG. 4 —is a method of forming constructing dynamometer card (Stage 2); 
         FIG. 5 —is a method of forming constructing dynamometer card (Stage 3); 
         FIG. 6 —is a polished rod load with a pump filling rate (example 1); 
         FIG. 7 —is a polished rod load with a pump filling rate (example 2); 
         FIG. 8 —is a polished rod load with a pump filling rate (example 3); 
         FIG. 9 —is an embodiment of the method of the sucker rod pump automated control and a flow control. 
     
    
    
     The following are definitions of some of the technical terms used in the detailed description of the preferred embodiments.
         a power balance—relation between the momentary power (MMP) and a counter weight system power (CWP) to a polished rod velocity.   walking beam angle sensor—rate-of-turn sensor; encode; rotation angle sensor.       

     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to  FIG. 1 , there is shown a sucker rod pump (SRP)  1  system comprises a variable speed drive (VSD)  2  equipped with a programmable controller (PC)  3  and connected with a motor  4 . The motor  4  is designed as a drive for the sucker rod pump crank  5 . Wherein the sucker rod pump crank  5  is in cinematic connection with a walking beam  7  through a link rod  6 . Wherein the walking beam  7  is connected to a polished rod  8 . The polished rod  8  provides transmission of reciprocating motion to the string of sucker rods  9  within a tubing string  10 . 
     On one embodiment of the invention, the walking beam  7  is equipped with an angle sensor  11  connected to the PC  3  input and is formed to detecting position of the walking beam. Wherein the PC  3  input is an analog input contains a power supply galvanic isolation, which provides immunity to power-frequency magnetic fields. 
     The PC  3  comprising an operating means based on a central processor unit (CPU)  3 . 1 . Referring to  FIG. 2  an automated control system of the sucker rod pump comprising: a means  12  of the crank  5  position detection based on the detected position of the walking beam  7 , a means  13  of the sucker rod pump  1  geometry dependences calculation, a means  14  of the motor  4  power calculation and a counter weight system  15  power (CWP) calculation, as well as means of the polished rod  8  velocity  16  and load  17  calculation. Wherein the polished rod  8  velocity and load values can be expressed through a power balance in the SRP  1  system. The calculated parameters used by a means  18  for data processing and forming a surface and a down hole dynamometer card of the sucker rod pump parameters. Said surface and the down hole dynamometer card are displayed on the screen of CP  3 , or another remount control device of the SRP automated control system. 
     The means  14  of the motor power calculation is made with a capability of the VSD active power calculation, by usage of a block  14 . 1  for a stator (P ST ) and a rotor (P RT ) power losses calculation and a block  14 . 2  of the sucker rod pump dynamic moment calculation. 
     Also, according to the one embodiment the means  18  for the data processing and forming the dynamometer cards is made with an ability of the polisher rod load zero portion calculation at the polished rod end points. Which is leading to an accuracy of forming and displaying of dynamometer cards. 
     Based on the described variant of the SRP system, the method of the SRP automated control can be implemented. 
     At the beginning of the SRP equipment operation, providing the automated control system calibration. The calibration is performing by the operator of the SRP. 
     During the SRP control system settings, providing calibration of the walking beam angle sensor  11 . Taking the motor torque reference value calculated on a first SRP stroke at a low motor velocity. Wherein the low motor velocity is up to 30% of nominal motor value. According to present invention said motor torque reference value showing a ratio between the motor torque average value and the sucker rod pump filling rate, wherein at least the sucker rod pump filling rate reflects changing of the polished rod load. 
     During the SRP commissioning, a number of parameters are also determined, the values of which remain unchanged during SRP operation and can be used in the calculation and performing of the dynamometer card. Among which, a moment of inertia formed by the motor  4  and by the counter weight system  15 , an inductance and a resistance motor parameter, parameters characterizing the geometry dependences of the SRP components. 
     According to the present embodiment, taking a linear dimension between the crank axis  19  and an anchor point between the link rod  6  and the crank  5 , a linear dimension between an anchor point of the link rod  6  and the walking beam  7  anchor point, a length of an arms of the walking beam  7 , a linear dimension between the walking beam  7  axes and the crank  5  axes, as well as a masses of counter weights system  15 . 
     Based on mentioned geometry dependences and calculated motor parameters calculating the dynamic moment which causing losses of the VFD dynamic power. 
     After SRP commissioning the control system is ready for exploitation. According to the present embodiment, the control method is based on the SRP dynamometer card, comprising a surface and a down hole dynamometer card ( FIG. 6-8 ). 
     Based on the dynamometer card data, forming the SRP motor control signals in accordance with the sucker rod pump filling rate. Also, the SRP motor control signals can be made, based on a load or/and a velocity of the polished rod. Wherein at least the motor torque, the polished rod load or/and the velocity are calculated based on mass and geometry values of the sucker rod pump components as well the as current and voltage parameters. 
     Calculating the power balance (P bal ) during the dynamometer card performing, wherein the motor power and the counter weight system power (CWP) excluding losses are corresponding to a power at an anchor point between the polished rod and the rod string. 
     According to the present invention performing of the surface dynamometer card comprising at least three main steps ( FIG. 3-6 ), one of which determines the value of the momentary power value (MMP) necessary to reciprocate the polished rod. 
     At the next step, the polished rod velocity is determined, and also at the next or one of the previous steps, the crank angle (φK) is determined. At the final step, using the result of the first steps, the power balance is determined, which is displayed graphically on the PC display. It is also possible to implement the invention, in which the results are displayed at the remote workplace of the operator of the automated control system. 
     At the step of determining the motor momentary power Pm, ( FIG. 4 ) necessary for the polished road reciprocating, using the means  14 , for calculating the VSD active power value (P VSD ), based on three-phase current (I ABC ) parameters, as well as the frequency setting (f) and the calculated voltage U value, in particular, the voltage vector angle (θ). Wherein changing the frequency setting (f) value relative to the sucker rod pump filling rate. After calculating active power value (P VSD ), taking the momentary power value required for polished rod reciprocation by excluding the losses. 
     In the above-mentioned embodiment of the invention, the SRP system power losses comprise a stator and a rotor loss of the motor, as well as the motor velocity change losses (P V ) (acceleration and braking of the system) and a mechanical loss. The stator losses are determined based on an amplitude value of the stator current and the stator resistance. The rotor losses are determined by using the rotor current calculated values as well as inductance and voltage. The acceleration/resistance losses take into account the parameters characterized by the dynamic moment of the system, which takes into account the geometric dependences between the SRP components, as well as the moments of inertia of the electric motor (Me) and the counter weight system power (CWP) (Pw), which are recorded into the PC memory block  21  during the commissioning step. 
     According to a preferred embodiment of the invention, the PC also contains a block of  20  of a smoothing filter (low-pass filters (LPF)), which allows forming the dynamometer card without interference of current harmonics and mechanical vibrations of the SRP system. Getting the MMP value required for polished road reciprocation after passing signals through the block  20  of smoothing filters. 
     At the second step ( FIG. 5 ), calculating the polished rod  8  velocity (V PR ). Wherein calculating the crank angle (φK) using the parameters of the SRP geometric dependences which are determined through the measured walking beam  7  angle (φB). The polished rod  8  displacement (S PR ) also calculated through the mentioned above values. During the polished rod  8  velocity calculation excluding a near-zero velocity values (V PR ≠0) at the walking beam  7  extreme points. 
     Calculating the load zero portion at the polished rod end points, wherein the load zero portion is forming a part of the polished road stroke length. Wherein forming the polished rod load constant value at an input/output of the zero portion, and forming an intermediate load value as a calculated mathematic value. Such variant, allows additionally take into account possible inaccuracies in the values of the SRP geometric dimensions. 
     On ( FIG. 6 ) is showing the final step of forming the surface or/and down hole dynamometer card. The dynamometer card is forming through the power balance of the SRP  1  system by using means  18  of the CPU  3 . 1 . In additional taking into account the motor momentary power value (MMP) calculated on the first steps, and a counter weight system power (Pw) during each reciprocating stroke of the polished rod  8 . Wherein, also counting the crank angle (φK), the polished rod velocity (V PR ) and displacement (S PR ). Wherein a visualization rate is depending on the time of one polished rod reciprocating cycle, calculated between two successive upstrokes. 
     The obtained dynamometer cards ( FIG. 6-8 ) are used by the SRP control system to generate control signals depending on the sucker rod pump filling rate. In particular, ( FIG. 6 ) shows the results of the SRP system operation according to the claimed method, wherein when the polished rod displacement graph  22  shows the SRP filling rate ( FIG. 6 ) dropping down equal to 56% which leads to a related polished rod load showed at graph  23 . As we can see on  FIG. 6  the estimated surface  22 . 1  dynamometer card is close to the measured surface  22 . 2  dynamometer card as well as down hole dynamometer card  22 . 3 . 
       FIG. 6  shows that changing the frequency setting and increasing the polished rod velocity V PR , are leading the optimal filling rate ( FIG. 8 ). 
     The dynamic changes of the SRP system operation are shown on ( FIG. 9 ). An example of the SRP control system operation with the flow rate optimization are shown (graph  24  depending on changing the motor velocity value (graph  25 ). In the given example ( FIG. 9 ), before the start of recording, the filling rate was set to 80% and the SRP system is reaching the maximum pumping of 4.16 pumps/min (65 Hz)—the moment the recording started. Further, at the time 11.46.40, the filling rate set was increased to 90%. After that, the SRP control system providing the flow rate optimization mode. The flow rate optimization mode anticipating a cyclic work with providing an optimized flow rate and maintaining the SRP filling rate. 
     The SRP filling rate, in one of the invention embodiments, also obtained by calculating the motor torque average value per each cycle (calculated between two successive upstrokes). In this option, the calculation of the motor torque average value calculated at low velocity, equal to 30% of the nominal value, and is taken the pump filling rate as 100%. Next, during each period of the SRP operation, the current average torque is comparing to the reference value, based on the achieved result calculating the percentage relation, which shows the percentage of the SRP filling (the dependence is shown in  FIG. 6-8 ). 
     The implementation of the described invention contributes to the achievement of the claimed technical result, increasing the accuracy of measuring the of the SRP characteristics, ensuring real time well flow rate optimization, as well as a continuity of the technological process with the possibility of changing the main parameters.