Downhole Card Analysis for Rod Pump Valve Position Detection
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Solution Overview
Problem
In deep wells, the long sucker rod's stretch and distributed mass cause significant differences in motion between the pump end and the upper end, making it challenging to accurately determine valve opening and closing positions and pump performance using existing methods, which are not robust enough to account for elasticity, viscous friction, and mechanical friction.
Innovation Solution
The use of the one-dimensional damped wave equation to calculate downhole position and load from surface data, allowing for the creation of a downhole card that enables the identification of valve opening and closing points, pump fillage, and fluid load by normalizing load and position vectors and performing slope vector analysis.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional surface card methods are used to determine pump performance, then the analysis is simple, but the accuracy is insufficient for deep wells with long sucker rods
Solution Approach 1:
The patent replaces traditional mechanical surface card analysis with a computational model based on the one-dimensional damped wave equation. This substitution allows accurate determination of downhole valve positions by processing surface measurements through mathematical modeling that accounts for rod elasticity, distributed mass, and friction effects, thereby achieving high measurement precision without requiring complex downhole instrumentation.
Solution Approach 2:
The patent introduces an intermediary computational layer between surface measurements and downhole condition analysis. The one-dimensional damped wave equation acts as a mediator that translates surface card data into accurate downhole valve position information, accounting for the complex physical effects in the rod string without requiring direct downhole measurement devices.
2Measurement precision
If the one-dimensional damped wave equation is used to calculate downhole conditions, then the accuracy of valve position determination is improved, but the computational complexity increases
Solution Approach 1:
The patent transforms the complex partial differential wave equation into a more manageable form by changing parameters and making reasonable assumptions for field conditions. This allows the model to maintain high accuracy for determining valve opening and closing positions while reducing computational complexity to a level suitable for practical implementation in well analysis.
3Reliability
If rod string elasticity and distributed mass are considered in the analysis, then the accuracy for deep wells is improved, but the calculation becomes more complex
Solution Approach 1:
The patent replaces simplified mechanical assumptions with a more comprehensive physical model based on the one-dimensional damped wave equation. This substitution incorporates rod string elasticity and distributed mass effects, significantly improving the reliability of pump performance analysis for deep wells while managing computational complexity through appropriate mathematical formulation.
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
This method provides an accurate and robust way to calculate valve opening and closing points, pump fillage, and fluid load, enabling effective control and optimization of rod pump performance by accounting for various downhole conditions and energy losses.
Implementation Method 1
there are three forces coming into play when using rod pumping: elasticity, viscous friction, and mechanical friction
Implementation Method 2
Produced fluid being lifted to the surface creates a viscous force on the outer diameter of the rod string opposing its movement
Implementation Method 3
the rod string and couplings cause mechanical friction with its contact with the inner diameter of the tubing
Data Source
AI summary
A method for determining valve opening and closing positions in a downhole card for an oil and gas well, the method including: calculating a downhole card using surface data for load and rod position; normalizing the load and position values for the downhole card; calculating a slope function data set using load and position; using a slope function to find start and end indexes along the downhole card; for each start and end index determining its percentage of vertical range and percentage of horizontal range; assigning the end index having the minimum horizontal range with the maximum vertical range as the standing valve opening point; assigning the start index having the maximum horizontal range with the maximum vertical range as the standing valve closing point; assigning the start index having the minimum horizontal range with the minimum vertical range as the traveling valve closing point.