Abstract
Computation of total mechanical skin for perforated completions and comparison of various completion options is a challenge faced by Engineers involved in completion design/optimization. The topic of total mechanical skin calculation has been investigated by various authors. Karakas-Tariq (1991) proposed a method which is widely accepted by the industry for its simplicity, ease of use and a good theoretical basis. However, this method has a serious drawback in that it fails to give consistent, reasonable & continuous results if a parametric study is done on perforation length or invasion damage depth.
A review of Karakas-Tariq perforation and total mechanical skin model has been conducted and their shortcomings have been identified. The calculated total mechanical skin is discontinuous and illogical as the perforation length crosses the damage boundary (for a fixed damage depth) or as the damage boundary crosses the perforation tunnel tip (for a fixed perforation length). Various techniques have been tried to solve this problem. An ideal solution should honour the Karakas-Tariq model for perforation tunnels terminating some distance away from the damage boundary and should give reasonable and continuous results as the perforation tunnel reaches or extends beyond the damage boundary. The proposed solution, developed using analytical equations, achieves this desired outcome. Flow has been split between a stream which passes through the damaged zone and the stream which goes directly into the perforation tunnels. The resulting modified Karakas-Tariq method has been extensively scenario tested with synthetic & published well completion data and results are encouraging. This improved method now can be incorporated in any comprehensive perforation/inflow modeling software for comparing various completion options.
