Very low permeability reservoirs are commonly developed with hydraulically fractured wells. Quite often, drilling costs must be reduced and/or the number of slots on an offshore platform is limited. Vertical wells are then replaced by a horizontal well with a set of parallel, equal size hydraulic fractures. A recurrent question concerns the productivity index of this multiply fractured horizontal well.

Simple analytical expressions of this index have been provided by Mukherjee et al.1 and later corrected by Lietard et al.2 They however underestimate to a large extent the actual performance of this type of well.

The present paper proposes a much better definition of the productivity index of multiply fractured wells. It is based on the usage of Dietz’ shape factors3 for vertical wells centered in independent box-shaped drainage areas of equal size in the considered reservoir. For this purpose, Gringarten’s work4 about shape factors for hydraulically fractured wells has been revisited, and corrected equations are presented in this paper.

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