Calculation of Static Pressure Gradients in Gas Wells

Abstract

Abstract The derivations of three methods of computing the static pressure gradientsin natural gas wells have been presented to show the assumptions made. Chartswere developed from which the pressure gradients may be read when the well-headpressure, the well fluid gravity, depth, and the average well temperature aregiven. A chart for estimating the well fluid gravity from the condensatecontent and separator gas gravity is included. The effect of the increasedaverage well temperature after flow on the calculation of the static pressuregradient is discussed. Introduction Reservoir pressures have been calculated from well-head pressures for gaswells for many years. As the pressure measurements become more accurate, theneed for a reliable calculation of the static pressure gradient often arises.This paper will develop the several methods for computing the pressure gradientin gas wells and make a comparison between them. The method of calculating static pressure gradients in common use is Eq. I(ref. I) or its counterpart which includes a factor for the deviation of thegas from the ideal gas law. An alternate method is to compute the average density of the gas in the welland multiply by the well depth in a manner similar to that used for liquidgradients. Derivation of Formulas A static pressure gradient is a special case of the general fluid-flowequation. Consider a pound of fluid flowing in a vertical column from point Ito point 2, Fig. I. T.P. 1814