New Sucker-Rod Pumping System Design Calculator Provides Free, Convenient Analysis On-Line

Unico has developed a convenient design tool for analyzing sucker-rod pumping (SRP) system performance. The SRP Calculator™ is available on-line free of charge and provides a quick, easy analysis for many systems.

Sucker-rod pumping systems involve complex dynamic relationships between production rates and stresses at various points within the unit. As a result, numerous calculations are required to optimize the effectiveness of these types of systems. The popularity of rod-pump systems has lead to a variety of methods for analyzing their performance.

In 1954, a group of users and manufacturers undertook a study of sucker-rod pumping systems. Their results eventually led to the publication of Recommended Practice for Design Calculations for Sucker Rod Pumping Systems (RP 11L) in 1988 by the American Petroleum Institute (API). This publication set the standard for analyzing rod pumps until recently, when personal computer calculation programs, such as Theta Enterprises' Rodstar and others, became available.

These PC-based analysis programs generally include an extensive database of pumping units and rod-string components. They are capable of analysis that correlates to actual field measurements with amazing precision. In many situations, however, this precision is unnecessary, and often it greatly exceeds what can be measured at the well site.

Unico's SRP Calculator™ satisfies the need for simple well analysis. It can be used to quickly analyze well performance to determine if a more detailed analysis is necessary.

Input and output variables generally follow those provided for the API publication and commercial analysis programs. The API method suffers from the fact that it does not account for performance differences between Class I (conventional) and Class III (Mark II) geometries. While rod loads may be similar between the two types of pumping units, there is a significant reduction in Class III gearbox torque relative to the Class I geometry.

Several parameters were added to the API method that improve the agreement between the SRP Calculator™ and commercially available analysis programs. A comparison of the features of the various rod-pump analysis tools is given below.

Analysis Tool Feature Comparison

The results of the SRP Calculator™, the Rodstar program, and the API RP 11L method are compared below for both Class I and Class III well examples. The relative error of most of the SRP Calculator™ calculations, which use some simplifying assumptions, is 10% or less, with many being within 5%. The only significant difference between the SRP Calculator™ and the Rodstar program occurs with the minimum motor size, for which the Unico program was able to select a smaller motor on the Class III pump. A number of results fall between those estimated by the Rodstar program and the API method. Additional care should be taken with values that fall to one side or another of both other methods. Generally, the SRP Calculator™ provides somewhat better results for Class I than Class III pumping units.

Analysis Comparison (Class I Example)

Analysis Comparison (Class III Example)

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In Future Issues...

Look for the following articles in upcoming issues of Oil & Gas Automation Solutions:

	Taking advantage of utility rate structures to reduce artificial-lift energy costs
	Unico drives plot and control pump fill using inferred downhole dynamometer graphs
	Power loss components in a typical rod pumping system
	A novel way of conceptualizing the effectiveness of artificial lifts
	Reducing power consumption and improving power factor of beam pumps
	Detecting PCP stick/slip oscillations that fatigue rod-string couplings and reduce energy efficiency
	Embedded well control is engineered for compatibility with Rotaflex® units

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