Productivity of cased and perforated wellbores completed with standalone screen depends on the interactions of parameters such as perforation diameter, length, phasing and density, the gap between the casing and the standalone screen, and standalone screen aperture/pore size. Moreover, the permeability of the sand in the gap plays a major role in the overall productivity. This study aims at providing a numerical estimation of pressure drop for such completions.
This study uses Computational Fluid Dynamics (CFD) in order to simulate the flow around a wellbore equipped with cased and perforated completion with standalone screen. Slotted liner was used as the standalone screen in this study. Details of such a complex completion were imported into the Finite Volume (FV) based numerical simulation via Computer-Aided Design (CAD). In addition to the geometrical design of the completion, different scenarios for the perforation stability, which affect the permeability of the perforation tunnel and result in potential fill-up of the annular gap between the slotted liner and perforations, were investigated.
A large number of simulations (over 200 models) were completed to cover the different scenarios for perforation design and strategy along with different Open to Flow Area (OFA) values for the standalone slotted liner. Based on the results, completion efficiency is strongly changed by perforation and gap flow properties. The OFA for the standalone slotted liner completion has minor influence on the overall pressure drop if the gap between the casing and the standalone screen and the perforation is clean, unless the perforations are collapsed and the annular gap between the casing and slotted liner is filled up with sand. This is mainly because perforation parameters, such as penetration and diameter dominate the effect of all the other parameters, including slotted liner configuration. The results emphasize the effect of the completion geometry, perforation strategy, and opening size on the skin and productivity. Another main observation was the need to better understand the stability of the perforations and sanding potential from perforations, which dictate the permeability of the perforation and annular space.
The results of this study highlight the comparative importance of different standalone screen designs and perforation parameters on well productivity. This study is the basis for optimizing the sand control and perforation strategy as an alternative to other completion types such as gravel packing in cased and perforated completions in vertical and slant wells.