The Performance of Perforated Completions in Gas Reservoirs

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Abstract
Although investigational work has been conducted to determine the performance of perforated completions in oil wells, not much is known about the performance of perforated completions in gas reservoirs. It is the objective of this paper to help fill this gap. A finite-element program was used to study in great detail the effects of perforation geometry and formation properties in the performance of completed gas wells. More specifically, the influences of (i) shot density, (ii) perforation length, (iii) phasing angle, (iv) formation permeability, (v) formation anisotropy and (vi) turbulence factor were studied. The results include the following: (i) In gas reservoirs with drawdown in the order of Δp2 = 6.75 × 106psi2 (Δp = 1500psi), turbulence effects are negligible when the horizontal permeability is equal to or less than 10 md., but can be very significant if the permeability is in the order of 1 darcy or more, (ii) When turbulence effects are not dominant, perforation length and phasing angle can affect productivity ratios, (iii) In anisotropic formations high shot density (≥ 12 shots/ft) with deep penetration (≥ 15 in.) is required for the well to perform better than an open hole completion; (iv) Turbulence effects can cause up to 74% loss in production in high-permeability formations. The nomograph generated in this paper can be used to predict productivity ratios and skin factors in gas reservoirs.

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