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Abstract

Dimensionless IPR curves for predicting the current and future performance of both unfractured gas wells, and fractured gas wells with positive, negative, or zero skin factors are presented in this paper. An example is presented in which the current and future performance of a gas well is forecasted and compared to the results obtained from a modified isochronal test.

Introduction

Forecasting well performance using dimensionless inflow performance (IPA) curves has its roots in the oil industry. Vogel and Standing presented dimensionless IPR curves for predicting the performance of oil wells under a variety of producing conditions. Utilization of these curves requires a knowledge of a flowing oil well's static bottom-hole pressure, its flow efficiency, and a stabilized flowing bottom-hole pressure measured at some constant oil production rate. This. data is used to construct an IPR curve for the well which can in turn be used to predict the ability of the well to produce fluids against a specified sandface backpressure.

Gas well production forecasting has historically depended on some form of multiple rate deliverability test, such as the U.S..Bureau of mines conventional backpressure tell the isochronal test, or the modified isochronal test. Recent attention has turned toward finding a reliable deliverability testing method that requires only a single flow test and shut-in period.

Research, by Mishra and Caudle, and Chase and Williams has focused on the development of dimensionless IPR curves for use in predicting the performance of gas wells. The chief advantage in using these IPR curves for predicting gas well performance lies in the fact that only a single stabilized flow test, along with a knowledge of the static bottom-hole pressure and skin factor for a well, are needed to characterize current or future well deliverability.

This paper presents a summary of the dimensionless IPR curves which are currently available for predicting the performance of gas wells. An application of these curves for predicting the performance of a gas well is given.

DIMENSIONLESS IPR CURVES FOR UNFRACTURED WELLS

Mishra and Caudle constructed dimensionless IPR curves for predicting the current and future deliverability of an unfractured gas well. These curves are shown in Figures 1 and 2, respectively. Mishra and Caudle did not distinguish between unfractured gas wells having positive, negative, or zero skin factors, therefore further research in this area may be warranted.

The equation describing the current dimensionless IPR curve in Fig. 1 is given by:

..........................................(1)

The equation representing the dimensionless IPR curve shown in Fig. 2 for predicting future performance of an unfractured gas well is:

..........................................(2)

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