Horizontal wells are becoming popular for primary and enhanced oil recovery operations because of unique advantages of horizontal wells in comparison to those for vertical wells. However, horizontal well testing is considerably more complex than vertical well testing.

This study uses numerical integration to evaluate an analytical solution for the transient pressure response of a horizontal well located in a closed, box-shaped, anisotropic reservoir. Results from this study show that numerical integration can be used to evaluate the solution with a comparative degree of accuracy, while avoiding the convergence problems associated with the analytical integration. Both drawdown and buildup responses have been studied.

New time criteria, based on the semi-log pressure derivative response, are proposed for well test analysis and design purposes. These time criteria generally suggest shorter flow period durations than those corresponding to the time criteria based on the pressure response. The effects of well radius, well location and reservoir size on the drawdown pressure derivative response are discussed.

Producing time effects on the buildup pressure derivative responses are also investigated. Results show that for a horizontal well in a closed reservoir, the late linear flow period will not occur on the buildup response for any case, even when the late linear flow period is present on the drawdown response. Design equations are presented for the time at which buildup response deviates away from the corresponding drawdown response to establish the applicability and limitations of using drawdown type curves to analyze buildup data obtained from a horizontal well.

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