A New General Pressure Analysis Procedure for Slug Tests

Abstract

Abstract A new method for determining formation flow capacity and skin factor from slug test data is presented. The new procedure is based on an exact deconvolution equation that converts the measured slug test pressure data into an equivalent pressure response that would be obtained if the well were produced at a constant surface flow rate. The new technique does not require the knowledge of the sandface flow rate and does not depend on the flow regime which exists within the reservoir. This procedure also yields the equivalent pressure derivative of the constant surface flow rate wellbore storage and skin pressure solution without applying numerical differentiation. After the constant surface rate pressure data and its derivative are generated by our procedure, the converted data can be analyzed by using existent wellbore storage and skin type curves for the particular reservoir model represented by the data. Therefore, slug test type curves are no longer needed. However, if the duration of the slug test is short, most of the converted data will fall on the unit slope line of the conventional constant rate wellbore storage and skin type curves, and thus, it will be difficult to obtain a unique type-curve match. For such cases, it is shown that the well known rate normalization procedure can be applied to greatly improve the reliability of the analysis. It is also shown that once the flow geometry is properly identified, the traditional superposition method (convolution) can be applied to the converted pressure data. A field case illustrating the reliability of the new method and its advantages over the traditional slug test analysis procedures is presented. This paper is dedicated to Dr. Henry J. Ramey, Jr. in deep appreciation of his profound and inspirational contributions to the fields of pressure transient analysis and reservoir engineering.