Pumping Unit Motor Speed Control for Rod Float Prevention
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing pumping unit technologies fail to effectively prevent rod float, a condition where the polished rod separates from the carrier bar, leading to overloading and shock loading, due to inadequate control over motor speed and load during the downstroke, especially in high viscosity oil applications.
Innovation Solution
The method involves determining the first angle of the crank arm and the corresponding torque factor, which includes the rate of change in polished rod position, to control the motor speed and load of the polished rod, maintaining a substantially constant speed and load to prevent rod float and reduce operational stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If motor speed is increased to maximize productivity, then cycle speed increases, but rod float occurs causing overloading and shock loading
Solution Approach 1:
The patent applies dynamics by making the motor speed variable rather than constant. The controller dynamically adjusts motor speed based on real-time detection of polished rod position and load conditions. During the downstroke, when rod float risk is highest, the controller reduces motor speed to maintain reliable connection between polished rod and carrier bar, while allowing higher speeds during other phases to maximize productivity.
Solution Approach 2:
The patent implements feedback control by continuously monitoring polished rod position (via position transducers) and load conditions (via load cells), then using this feedback to adjust motor speed in real-time. The controller receives feedback signals about rod float conditions and automatically modifies operating parameters to prevent rod float while maintaining optimal cycle speed.
2Reliability
If motor speed is reduced to prevent rod float, then reliability improves, but productivity decreases
Solution Approach 1:
The patent applies periodic action by implementing different speed control strategies for different phases of the pumping cycle. The controller detects the downstroke phase (when rod float occurs) and applies reduced speed specifically during this periodic interval, while maintaining or increasing speed during upstroke and other phases. This periodic modulation of speed prevents rod float without sacrificing overall productivity.
Solution Approach 2:
The patent applies local quality by applying different speed control characteristics to different portions of the operating cycle. Instead of uniformly reducing speed throughout, the controller applies speed reduction only locally during the critical downstroke phase where rod float risk exists, while allowing full or enhanced speed during other phases, thus maintaining high overall productivity while preventing rod float.
3Device complexity
If conventional control methods are used, then device complexity remains low, but rod float cannot be effectively detected or prevented
Solution Approach 1:
The patent introduces intermediary sensing elements (position transducers and load cells) that mediate between the physical rod float condition and the controller. These intermediaries detect subtle changes in polished rod position and load that indicate impending rod float, translating physical conditions into electrical signals that the controller can process to trigger preventive speed adjustment.
Solution Approach 2:
The patent replaces conventional purely mechanical speed control with an electromechanical control system. Electronic sensors and a programmable controller substitute for mechanical governors or linkages, enabling more precise and adaptive detection of rod float conditions and more sophisticated speed modulation to prevent rod float while maintaining productivity.
Data Source
Figure 1
Figure 2
Figure 3
AI summary
Methods and apparatus to determine operating parameters of a pumping unit for use with wells are disclosed. An example apparatus includes a housing and a processor positioned in the housing. The processor is to determine a rate at which to operate a motor of a pumping unit to enable a load imparted on a polished rod of the pumping unit to be within a threshold of a reference load or to enable a speed of the polished rod to be within a threshold of a reference speed.