Abstract

Reservoir deposition occurs over geologic period of time and thus, most of the reservoirs are layered in nature. These layers may or may not communicate with each other. This study develops a new semi-analytical model for pressure transient analysis of layered gas reservoirs. Apart from layering, in a gas reservoir the flow problem is further complicated by high velocity effect, pressure dependent gas properties, and wellbore storage and skin. Discretizing only the vertical direction term to account for the cross flow, and using pseudopressure and pseudotime approach, the diffusivity equation has been solved as a generalized eigenvalue problem. The model takes into account inter-layer crossflow, high velocity effects, wellbore storage and skin (both as thin skin and finite damaged zone), and different possible inner and outer boundary conditions.

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