Simulation of Gas Well Performance Using Tabular-Graphical Techniques

Abstract

With the graphs and techniques proposed here, the past performance of "real gas" wells can be analyzed and the future performance predicted without the need for costly computer calculations. When the available reservoir data are of questionable accuracy, this system helps to establish the extent of their reliability. Introduction The productive capability and pressure history of a gas well throughout its life, as well as reserve estimates and production rates, can be determined quickly using the graphical methods presented in this paper. Figs. 1 and 2 were constructed from data paper. Figs. 1 and 2 were constructed from data calculated by computer program for "real gas" flowing under semisteady-state conditions using assumed values for gas gravities and reservoir temperatures. Further use of the computer when analyzing gas wells merely duplicates data available from Appendix A of this paper. Fig. 1 relates sand-face pressure with the average reservoir pressure and Fig. 2 relates average reservoir pressure with gas volume and p/z. Turbulent flow is pressure with gas volume and p/z. Turbulent flow is handled as a variable skin. Hydraulic fractures and such changes with time as sand-face pressure, flow rates and skin, are easily handled. When permeability and skin can be separated by independent methods, the methods conform with theory. When kh and s cannot be separated, field application continues to be accurate within the range of normal field basic data. The technique enables the engineer to simulate quickly gas well performance throughout life, determine errors in basic data and evaluate the risks inherent in basic field data of unknown accuracy. (This is done without the computer in less time than is required to fill out computer input forms.) Such understanding is often lacking when computer runs are made using a few indicated or assumed reservoir conditions of questionable accuracy. The method also enables the engineer to compare buildup results and prior production performance, to evaluate possible prior production performance, to evaluate possible results of remedial operations, to select the best remedial operation, to size compressors and tubing, and in general to understand gas well behavior. There is a need for accurate data on pressure and production rate during the productive life of gas wells. production rate during the productive life of gas wells. The program of data collection proposed here is much more valuable than the currently accepted practice of obtaining pressures after short shut-in periods. The data actually required to analyze properly the performance of gas wells can be collected by this system performance of gas wells can be collected by this system at no additional expense and they replace unusable and misleading information often routinely collected at considerable expense. Construction of Basic Graphs Data shown in the figures have been computed by a machine program that converts "real gas" to ideal gas conditions. The approach used is described by Russell et al. Other approaches such as described by Ramey et al. could have been used instead. For semisteady-state flow, the basic formula involved reduces to: ...............(1) JPT P. 1202