The fracturing of horizontal wells has recently gained wide acceptance as a viable completion option to maximize the return on investment. This is especially true in the case of tight formations.

This paper presents an analytical model for fractured horizontal wells in anisotropic closed or semi-infinite, homogenous or naturally fractured systems. Uniform flux, infinite conductivity and finite conductivity models are considered. The fractures may be of different properties and unequally spaced along the horizontal wellbore. This model is validated using a numerical simulator. It provides us with methods and ideas for designing, interpreting well tests and prediction of the long time performance of the system under study.

A log-log plot of pressure and pressure derivative versus test time may reveal the presence of several straight lines corresponding to different flow regimes: bilinear, first linear, biradial, radial, pseudoradial, second linear and pseudo steady state.

New equations have been developed describing the unique characteristics of these flow regimes. These equations allow us to calculate: the number of active fractures, equivalent fracture conductivity and total system conductivity, equivalent half-fracture length, reservoir directional permabilities, equivalent skin, the total skin, reservoir width for semi-infinite systems and drainage area for closed systems.

Simulated examples have been performed to show the applicability of the proposed technique.

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