Speed control

• US 4,145,161 A
• Filed: 08/10/1977
• Issued: 03/20/1979
• Est. Priority Date: 08/10/1977
• Status: Expired due to Term

• Current Assignee: Amoco Corporation (BP PLC)
• Original Assignee: Standard Oil Company (BP PLC)
• Inventors: Skinner, David R.
• Primary Examiner(s): Freeh, William L.
• Application Number:
  US05/823,292
• Time in Patent Office: 587 Days
• Field of Search: 417/42, 417/22, 417/53
• US Class Current: 417/22
• CPC Class Codes: E21B 43/127 Adaptations of walking-beam pump systems
• CPC Class Codes: F04B 2203/0208 Power
• CPC Class Codes: F04B 2203/0209 Rotational speed
• CPC Class Codes: F04B 49/065 and making use of computers
• CPC Class Codes: H02P 23/14 Estimation or adaptation of motor parameters, e.g. rotor time constant, flux, speed, current or voltage

Abstract

This is a method and apparatus for controlling an oil-well beam pumping unit in a manner which allows increased oil production. The AC electric motor of the beam pumping unit is supplied power through a variable frequency power supply, whose frequency (and voltage) is controlled by circuitry to automatically adjust to whatever flow enters the wellbore by varying the speed of the pumping unit to maintain the speed generally proportional to the real power consumed by the pump. As the level in the wellbore can be maintained at an essentially constant minimum level, despite the relatively large hour-to-hour variations in in-flow which normally occur, the total flow from the formation into the wellbore in a given period of time is increased.

Claims

1. A variable pumping speed control system for a beam pumping unit in which a down-hole pump is actuated by a rod string driven by an AC motor, said system comprising:

(a) means for generating a signal indicative of real power supplied to the pump;

(b) means for generating a signal which is a function of pumping speed;

(c) a variable frequency power supply having a signal input, a power input and a power output, said power input being connectable to a source of AC power, and said power output adapted to be connected to said AC motor; and

(d) control circuitry having inputs adapted to receive said real power signal and said speed signal and an output connected to said signal input of said variable frequency power supply, said control circuitry being adapted to vary the output of said variable frequency power supply to maintain said speed signal essentially directly proportional to said real power signal.

2. The control system of claim 1, wherein said real power sensing means comprises a wattmeter connected to sense power supplied to said AC motor.

3. In combination with a beam pumping unit of the type wherein an AC motor mechanically actuates a pump by means of a rod string, the improvement comprising:

(a) real power sensing means;

(b) speed sensing means;

(c) a variable frequency power supply having a signal input, a power input, and an output, with said power input being connectable to an AC power line and said output being connected to said AC motor; and

(d) controller circuitry having inputs connected to said real power sensing means and said speed sensing means and an output connected to said variable frequency power supply signal input, said circuitry being adapted to generate an output signal to cause said variable frequency power supply to vary its output frequency to maintain pumping speed essentially directly proportional to the real power of said pump.

4. The combination of claim 3, wherein said real power sensing means is a semiconductor wattmeter, which monitors the output of said variable frequency power supply.

5. A method of operating a beam pumping unit driven by an AC motor, said method comprising:

(a) generating a signal which is a function of the real power of said pump;

(b) generating a signal which is a function of pumping speed;

(c) comparing said real power signal and said speed signal and generating a speed demand signal adapted to maintain the speed of said beam pumping unit essentially directly proportional to said real power signal;

(d) controlling the frequency of a variable frequency power supply in response to said speed demand signal; and

(e) supplying the output of said variable frequency power supply to said AC motor.