The New Research of Subsurface System Performance Curves of Sucker-Rod-Pumping
Authors: Zhao Ruidong , Zhang Jianjun , Tao Zhen , Tian Jinxiu , Huang Shicai , Shi Junfeng , Xiong Chunming , Zhang Xin , Zhu Shidong , Wang Yuxia 
Published: March 2015

Abstract
Sucker rod pumping system is the mechanical oil production method first used, up to now, it is also the most widely applied artificial lift method, however, three performance curves (displacement ~pump differential pressure, displacement ~ horsepower, displacement ~ efficiency) of sucker rod pumping (SRP), which are equivalent to those of electric submersible pump(ESP) and progressive cavity pump(PCP), are not available, increasing the complexity when node analyzing and designing of SRP well. As is known to all, when optimization design of SRP well, trial method is generally used and the operating time is long.
Considering the interference of tubing, rod, wellbore fluid and piston pump when working, the subsurface system could be studied as a whole, and the relations between displacement and pump differential pressure, horsepower and pump differential pressure are researched. The dimensionless performance curves of SRP can be obtained based on API RP 11L standard.
Three performance curves of subsurface system, namely the relation curves of displacement ~pump differential pressure, displacement ~ horsepower, displacement ~ efficiency, are drawn for the first time. The characteristics of these performance curves are analyzed, showing these curves described in this article can effectively reflect the working characteristics of the subsurface system of SRP.
The subsurface performance curves can be a useful tool for sensitivity analysis and optimization design of SRP system. These curves allow developing a general nodal analysis algorithm for any artificial lift pumping method and a more convenient optimization design algorithm for composite pumping system, such as Jet- Rod pumping system.

Introduction
Sucker rod pumping downhole system can be seen as a special kind of plunger pump. There is a elastic rod string of several hundred to several thousand meters between polished rod and plunger pump, which is outstanding feature of the system[1]. When working underground, sucker rod pump is affected by elastic deformation of sucker rod and tubing, filling level of pump. So its performance is different from ordinary plunger pump.
The curve which is called pump's performance curve shows relationships among the main parameters. Essentially, pump's performance curve is the external representation of fluid's motion in pump system[2]. So any pump system should have its own performance curve, which can generally be obtained by actual measurements, such as electric submersible pump. But the performance curve cannot be obtained by measuring the ground equipment like ESP because of sucker rod pump's long rod and complex underground environments.
In order to get the performance curve of sucker rod pumping system, this paper is focused on API RP 11L standard[3] of American Petroleum Institute and put forward the concept of dimensionless performance curve of sucker rod pump which can be deduced by the curves in API RP 11L standard. The dimensionless performance curve can reflect the relationships among displacement, horsepower of polished rod, downhole efficiency and pump differential pressure. Due to assumptions of API method, the performance curve needs to be modified when applied in node analysis and optimization design.