Abstract

In this study, a mathematical model was developed to present pulse and interference testing for multilayered reservoirs. It was found that apparent storativity calculated from pulse testing data is always less than or equal to the actual storativity of the reservoir and that apparent transmissibility is always greater than or equal to the actual transmissibility. For short cycle intervals, the fractional production rate from a particular layer is not proportional to it's transmissibility fraction. The effect of storativity variation on fractional production rate is negligible. Wellbore damage affects both apparent transmissibility and storativity. Less accurate estimation of reservoir characteristics is obtained using pulse-test data as the contrast in reservoir properties increases and vice versa. A new approach is suggested to use data of single well test and pulse test to estimate properties of individual layers. The approach is demonstrated by a three-layer numerical example.

Introduction

Pulse testing is one of the most widely used techniques to predict interwell reservoir characteristics such as porosity and permeability. Johnson et al presented a technique to predict the reservoir properties between two wells or more. One of them is used as a pulser and the others are used as observers. The pulser is activated by changing flow rate to create a transient pressure disturbance. In the same time, very sensitive pressure gauges are used to measure pressure response at the observers. Johnson et al used such pulse testing data to estimate formation transmissibility and storativity. Vela and McKinley and Prats and Scott investigated the effects of areal heterogeneities and wellbore storage on pulse testing data. Woods proposed a method to estimate two zone reservoir characteristics using single well and pulse testing data. He found that apparent transmissibility obtained by pulse testing is always equal to or greater titan the total transmissibility of the two zones and that apparent storativity is always equal to or less than the total storativity of thee two zones. Correlation curves for pulse testing design and interpretation were developed by Brigham for equal pulse and shut-in periods. A set of correlation curves was developed by Kamal and Brigham for unequal pulse and shut-in periods. Such correlations can be used to optimize pulse ratio such that maximum response amplitude is obtained. Many applications of multi-well testing were reported in literature. Al-Khalifah et al presented a revision for Kamal and Brigham pulse testing correlation charts. El-Khatib presented new correlations for time lags and pressure response amplitude in pulse- test analysis.

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