Using the theory of impulse testing and principle of superposition, Nolte et al [1] developed a method which allows the identification of radial flow and thus the determination of reservoir transmissibility and reservoir pressure. The exhibition of the radial flow is ensured by conducting a specialized calibration test called mini-fall off test. Benelkadi and Tiab [2] proposed a new procedure for determining reservoir permeability and the average reservoir pressure in homogeneous reservoirs. In this paper, the procedure is extended to naturally fractured reservoirs. A new method for the determination of reservoir transmissibility using the after closure radial flow analysis of calibration tests was developed based on the pressure derivative. The primary objective of computing the pressure derivative with respect to the radial flow time function is to simplify and facilitate the identification of radial flow and the characteristic trough of a naturally fractured reservoir. The proposed method does not require a-priori the value of reservoir pressure. Only one log-log plot is used to determine the reservoir permeability, average pressure, storativity ratio, and interporosity flow coefficient. The technique is presented as a step-by-step procedure, with appropriate equations and graphs. The log-log diagnostic plot of pressure and the pressure derivative is employed here as the main tool to identify the radial flow regime and determine properties of a naturally fractured reservoir (I.e. permeability, interporosity, storativity ratio, and average reservoir pressure). The application of the proposed method is demonstrated on real field data from calibration tests. The main conclusion of this study is that small mini-fracture treatments can be used as an effective tool to identify the presence of natural fractures and determine reservoir properties.
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