A Computer Technique for Analyzing Pumping Well Performance

Abstract

Abstract A computerized analytical technique for investigating sucker rod pumping well performance develops load-position values (dynagraphs) at the pump, at desired points in the rod string and at the polished rod through use of a mathematical model of the sucker rod installation. Using the load-position diagrams of the pump, junction points and polished rod, quantitative deductions may be made regarding the mechanical condition and performance of the down-hole equipment (rod string, pump, tubing anchor, etc.) and the physical properties of the well itself (pump submergence, gas interference, fluid pound, etc.). Analysis of subsurface dynagraphs from several cave histories is discussed. Introduction Production men have recognized for years that a more complete knowledge of rod pumping performance would suggest means of lowering lifting costs, making more appropriate installation designs and increasing the proportion of oil economically recoverable by rod pumping. It was this need for knowledge that led to intensive studies from 1927 to 1943. During those years the polished rod dynamometer (1927), the bottom-hole pressure bomb (1929), the pump dynagraph (1936) and the sonic fluid-level sounder (1936) were developed. During that time many engineers used those tools to develop the theories on which our present knowledge of sucker rod pumping is based. Contributions made since 1943, in an effort to correlate data obtained from the various instruments, are mostly elaborations and refinements of the basic principles established during the preceding period. A notable exception is the Gibbs-Neely mathematical technique that analyzes pumping well performance with a digital computer. In effect, the technique yields all the information derived from these mechanical devices but has the added advantage of requiring only one series of measurements taken and recorded at the polished rod. Technique Procedure In application, polished rod data are recorded on the strip chart of a Delta II Dynamometer that consists of a dual-channel, carrier-amplifier recorder, a strain gauge-type load cell (for the polished rod loads) and a position transducer (for the instantaneous polished rod position). Eickmeier and Herbert described in detail the dynamometer, its components and its use. Polished rod data recorded at the well site, pertinent well data concerning down-hole equipment and known operating conditions are submitted to the computer for mathematical decoding. The computer output is plotted as load-position diagrams at the surface, at desired points in the rod string (i.e., junctions in tapered strings) and at the pump (similar to the Gilbert pump dynagraph). The loading information at junction points is extremely useful in analyzing sucker rod failures. Table I summarizes the various criteria evaluated by the computer technique and emphasizes its advantages over visual interpretation of a mechanical dynamometer card. Case Histories The pump cards and polished rod cards examined here are taken from some 1,000 well surveys run in the past 2 years throughout the United States, Canada, Colombia and Venezuela. They represent just a few of the downhole conditions detectable through the computer technique, and just a few of the cases where facts presented to the oil companies were acted upon to solve their problems. TABLE 1-CRITERIA EVALUATED BY COMPUTER Mechanical ComputerEvaluate Dynamometer Technique Surface loads and stresses Yes Yes Torsional analysis Yes Yes Pump dynagraph No Yes Maximum plunger stroke No Yes Effective plunger stroke No Yes Pump displacement No Yes Pump efficiency No Yes Plunger slippage No Yes Traveling-valve leak Possible Yes Standing-valve leak Possible Yes Gas interference Possible Yes Fluid pound Possible Yes Pump intake pressure No Yes Loads and stresses-tapered rod string No Yes Tubing movement No Yes Tubing anchor malfunction No Yes Packer malfunction No Yes JPT P. 243ˆ