A New General Pressure Analysis Procedure for Slug Tests

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.

Flowback Analysis for Fracture Characterization

“…Examples include injection/falloff test [5], fracture-calibration test [7], and slug test [8]. Examples include injection/falloff test [5], fracture-calibration test [7], and slug test [8].…”

Quantifying Skin Variation for Underbalanced Perforating

“…In other word, the analytical solutions used in these methods do not represent the entire pressure history in the tests. The second group of the methods handles the variable flow rate boundary condition by calculating the flow rate from a constant wellbore storage coefficient of a slug test (Ramey et al, 1972;Peres et al, 1993;Xiao and Reynolds, 1992;Rahman et al, 2005). If the well has relatively low energy, gas vaporization effect is not severe, and the pressure in the surge chamber does not change substantially, then the assumption of a constant wellbore storage is usually valid and these methods can be used to match the entire pressure data.…”

Integro-Differential Solutions for Formation Mechanical Damage Control During Oil Flow in Permeability-Pressure-Sensitive Reservoirs

“…In the Eq.6-20, the first double integral represents the drawdown period and, therefore, its derivative is expressed by the linear solution derivative in the interval [0, t pD ]. The second integral is related to the build-up term and its derivative must be taken with respect to the time superposition interval [t pD , t D ], (Peres, Onur & Reynolds;Lee;Johnston & Lee;Lee, Rollins & Spivey;Barreto Jr., Peres & Pires, 1989, 1982, 1991, 2003, 2010. The same procedure is applied to the diffusivity deviator factor ξ.…”