The paper demonstrates that the transient flow regime in multi-fractured horizontal wells, often interpreted as linear flow, is more likely elliptical flow. Elliptical flow often cannot be distinguished from linear flow at earliest times, but the apparent transition between transient linear flow and boundary-dominated flow may, in fact, be strongly affected by elliptical flow prior to being influenced by interference between adjacent fractures. Taking the elliptical flow regime into account can often improve our interpretation of production histories and our ability to forecast future production, thus improving economic evaluation and reserves estimation. We verified elliptical flow regimes by comparing production forecasts from existing semi-analytical and analytical solutions for multi-fractured horizontal wells. We then used asymptotic approximations to elliptical flow solutions to identify important flow regimes and to validate our model. On the basis of this work, we proposed new methods to determine reservoir properties and explored the parameters influencing the productivity of a multi-fractured horizontal well in a tight shale formation. Finally, we demonstrated, with a field example, the utility and applicability of our elliptical models and work flows for data analysis based on them. We emphasize our conclusion that transient linear models appear to be mere approximations of the more complete elliptical models during early flow periods in multi-fractured horizontal wells and thus open a question for debate: Is transient linear flow a myth (a mere approximation) or a real flow regime?
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