This paper presents interpretation of several transient tests conducted in a well with multiple horizontal drainholes. The subject well is located in the offshore divided zone of Saudi Arabia and Kuwait and was initially completed as a vertical producer. Recently, two medium-length horizontal drainholes, each in a separate layer, were drilled from the existing casing of this well. In order to evaluate the effectiveness of the horizontal completion, the well was subjected to four production tests before and immediately after the drilling of each drainhole. These flow tests were analyzed in detail to determine important reservoir and production characteristics. The observed pressure responses are compared with those obtained from analytical and numerical models. A discussion on the practical aspects of well test interpretation in horizontal drainholes is also provided.

Numerical simulations show that, for transient analysis purposes, most multiple drainhole systems can be approximated by an equivalent single-layer, single-drainhole systems. Additionally, the results demonstrate the importance of drainhole orientation when the vertical communication between the producing layers is not restricted by flow barriers.

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