Rod Pumping Unit Velocity Control via Load Feedback
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Solution Overview
Problem
Rod pumping units face reliability issues due to variable stress waves along the sucker rod string, causing fatigue, which existing controllers fail to mitigate effectively, as they primarily control fluid flow and tubing reliability by adjusting velocity with a single profile.
Innovation Solution
A control system for rod pumping units that includes a processor, memory device, and sensors to measure surface load and compute a desired velocity based on a reference velocity profile and force, allowing for variable speed control to manage stress waves and optimize pump production.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single velocity profile is used to control the rod pumping unit, then the control system is simple and easy to operate, but the sucker rod string experiences variable stress waves causing fatigue and reliability issues
Solution Approach 1:
The control system transitions from a static single velocity profile to a dynamic multi-velocity profile system that adapts in real-time. The controller receives position and load data from sensors and dynamically adjusts the pumping unit velocity through a variable speed drive, enabling the system to respond to changing operating conditions and mitigate stress waves on the sucker rod string.
Solution Approach 2:
The control system implements feedback mechanisms by continuously monitoring position via position sensors and load via load cells. This feedback information is fed back to the controller, which processes the data and adjusts the velocity profile accordingly, creating a closed-loop control system that optimizes reliability while managing complexity through intelligent control algorithms.
2Productivity
If pumping speed is increased to improve productivity, then fluid flow increases, but stress waves and fatigue on the sucker rod string worsen
Solution Approach 1:
The system uses dynamic velocity profiling that adjusts pumping speed based on real-time position and load conditions. Rather than maintaining a constant high speed, the controller modulates velocity throughout the stroke cycle, allowing high productivity during favorable conditions while reducing speed when stress wave risks increase, thus balancing productivity and reliability.
Solution Approach 2:
The control system changes the velocity parameter dynamically throughout the pumping cycle based on position and load feedback. By adjusting velocity as a variable parameter rather than a fixed value, the system can optimize fluid flow rate while simultaneously managing stress wave generation and sucker rod string fatigue, resolving the contradiction between productivity and reliability.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The system reduces load fluctuations, increases pumping speeds without increasing fatigue, and enhances fluid flow while ensuring the sucker rod string and well components are not damaged.
Implementation Method 1
a load cell configured to measure a surface load
Implementation Method 2
The sucker rod string behaves similarly to a spring over long distances. The sucker rod string elongates and retracts based on exposure to variable tensile stress.
Implementation Method 3
The sucker rod string responds to the varying motion by sending variable stress waves down its length to alter its own motion.
Implementation Method 4
The response of the sucker rod string is damped somewhat due to its submergence in a viscous fluid (water and oil)
Data Source
AI summary
A control system for a rod pumping unit is disclosed herein. The control system includes a memory device, a sensor, and a processor. The memory device is configured to store a velocity profile for controlling a sucker rod string of the rod pumping unit. The sensor is configured to take measurements for determining surface load of the sucker rod string. The processor is configured to gain access to the memory device and the velocity profile. The processor is further configured to determine a reference force. The processor is further configured to receive a measurement from the sensor and determine the surface load. The processor is further configured to compute a desired velocity for commanding the rod pumping unit. The desired velocity is computed based on a reference velocity from the velocity profile, the reference force, and the surface load.