During completion phase the casing perforation is considered one of the most critical parameters on formation damage, especially if the completion fluid interacts negatively with the reservoir. Tubing Conveyed Perforating (TCP) system is normally used to perforate low porosity & low permeability wells. However, in cases of completion with ESP the challenge is to avoid any contact between reservoir rock and completion fluid, otherwise the alternative solution is to run TCP in single run then kill the well after perforation in order to install the ESP completion. Based, in the presented case the well has been perforated in static underbalance condition with ESP in place and without killing the well. This approach prevents any contact between reservoir and completion fluid which reduce the completion skin to its minimum value. The technique has been successfully applied in Western Desert Agiba concession wells. The automatic release gun hanger and the gun string has been set against the required interval, then the ESP has been separately installed; the guns has been activated through an electronic firing head for a shoot-and-drop operation. The underbalance has been created by the ESP with the aid of the programmed delayed firing time. After this operation, the well has been directly lined up to production. Despite the challenge well conditions [reservoir depth exceeds 16,000 ft (4877 m), temperature of 285 °F (176.1 °C), porosity less than 8%] for which also the completion fluid specification is very sensitive to prevent the formation damage, the Productivity Index (PI) of the well was improved by 66% compared to the offset wells.
During the jet penetration process, some damage occurs to the rock matrix surrounding the perforation tunnel. The altered area, called the damaged (crushed and compacted) zone, results from high-impact pressures that occur during perforating. A damaged zone forming a layer approximately 0.25 to 0.5 in. around the perforation tunnel (Asadi and Preston, 1994 [1]; Pucknell and Behrmann, 1991[2]). Later work by Halleck et al. (1992) [3] shows that damaged zones are of non-uniform thickness and decrease down the length of the perforation tunnel. Laboratory studies indicate that the permeability of the damaged zone can be 10 to 20% of the surrounding formation (Bell et al., 1972) [4]. Accordingly, it is very important to design the perforation event to minimize this effect on well performance. Perforation-Damaged Zone.
