A Review of Methods for Design and Analysis of Rod Pumping Installations

Abstract

Summary Rod pumping continues to be the most widely used means for artificial lift of oil wells. Because of the wide use, the methods for design and analysis of rod pumping installations are being refined and improved continually. The current methods have evolved over the last 25 years from two sources:analog computer simulation, andpurely mathematical and digital simulation of the pumping system. This paper discusses applications of pumping system. This paper discusses applications of the two methods in design and analysis activities. Introduction The analog computer technology (API method) takes the form of nondimensional charts for prediction of rod loads, power requirements, pump strokes, and gearbox torques. These charts are suitable for manual calculations and form the basis for design and selection of equipment in new installations. Also, the analog computer technology leads to construction of synthetic dynamometer card catalogs that in some cases can aid dynamometer card interpretation and surveillance of existing wells. The paper gives a brief overview showing how the analog computer technology is used to design new installations and to analyze the operational effectiveness of existing installations. The purely mathematical and digital approach also has spawned methods for design and analysis. The design technique allows prediction of dynamometer cards for a wide variety of pumping equipment and downhole conditions. The paper cites several examples showing how the operating characteristic of various prime movers, pumping units, rod strings, and downhole pumps can be pumping units, rod strings, and downhole pumps can be anticipated. Finally, the mathematical approach has led to techniques for establishing opening conditions both at the surface and downhole in existing wells. These methods also allow estimation of production potential of the well--all from dynamometer data taken at the surface. The range of applicability and the limitations of the various techniques are compared. Historical Development of API Method What is now called the API method traces its history to work sponsored in the 1950s and 1960s by a nonprofit group called Sucker Rod Pumping Research Inc. This work was performed by Midwest Research Inst. and resulted in an analog computer simulation of the sucker rod pumping system. The analog computer results later were released to API and the API method came into existence. The sucker rod system was thought of in terms of the approximate mechanical system shown in Fig. 1. The springs simulated the elasticity of the sucker rod. the weights represented the mass of the rod, and the dash pots depicted frictional losses along the rod string. The pots depicted frictional losses along the rod string. The mechanical system was used to suggest the electrical analog computer, which in turn led to the nondimensional graphs. The following assumptions that underlie the API method are of extreme importance.Conventional pumping unit motion is presumed.Relatively low-slip prime movers are simulated.Steel rod strings are presumed. Tapered strings are simulated as if the rods become smaller with depth (i.e., no sinker bars).Normal downhole friction is simulated.The pump is assumed to fill completely with liquid (no gas interference or fluid pound).The mechanical predictions are made by presuming that the tubing is anchored.The pumping unit is assumed to be in balance. The API Method as a Design Tool The analog computer was used to construct a set of nondimensional design charts for selecting and sizing beam pumping equipment. pumping equipment. JPT P. 2931