TX 75083-3836, U.S.A., fax 01-972-952-9435.
AbstractThis paper presents the development of a new analysis technique that can be used to determine the gas-in-place for abnormally pressured gas reservoirs. This new approach requires only production data ( p G p and ) and does not require a prior knowledge of formation and fluid compressibility data. Using a pressure-dependent compressibility function based on the generalized gas material balance equation, this approach can be used to model both the rock collapse and shale water influx theories presented in the literature.In this work we introduce two new plotting functions: e c where these plotting functions are developed using the generalized gas material balance equation for a gas reservoir under the influence of a pressure-dependent formation compressibility function (Fetkovich, et al. 1 ) in conjunction with the two straight-line trends observed on the p/z versus G p plot for abnormally pressured gas reservoirs. Using these new plotting functions we develop a dynamic type curve matching technique that simultaneously determines the gas-in-place (G). In addition to gas-in-place, this new technique can be used to calculate pore volume compressibility as a function of reservoir pressure.We provide the verification of our new analysis technique using the results of numerical simulations and we demonstrate the application of this methodology using several field examples.R. GUNAWAN GAN AND T. A. BLASINGAME SPE 71514reservoir. The second (apparent) straight line p/z versus G p trend develops because of a decrease in pressure support from the surrounding shales as the gas reservoir is depleted. Bourgoyne derived a gas material balance that utilizes a constant effective compressibility term to account for the effect of water influx from shale (and/or a small steady-state aquifer).The primary objective of this paper is to show the development of a new methodology for the analysis of production data from abnormally pressured gas reservoirs. This method uses a pressure-dependent compressibility function to represent the rock collapse and shale water influx theories.
Literature ReviewMaterial balance analysis methods used to analyze production data from abnormally pressured gas reservoirs can be separated also into two categories -those methods which require prior knowledge of the various compressibility functions and those methods which use production data to obtain both an effective system compressibility and gas-in-place (as a simultaneous solution). Both categories of these methods will be briefly discussed in this section.
Methods Based on Knowledge of Compressibility Data.Hammerlindl Method. Hammerlindl 5 developed two methods for predicting gas-in-place using early pressure and production data. The first method estimates the apparent gas-in-place using the conventional p/z extrapolation of early reservoir performance and then "corrects" this estimate by using an average value of the ratio of effective compressibility to the gas compressibility (c e /c g ) avg .