Predicting Depth of Penetration of Downhole Perforators

Abstract

Abstract Productivity of a cased-and-perforated well depends on completion parameters (charge, shot density and phasing), formation properties (lithology, anisotropy, permeability, fluid properties and saturations), and environmental conditions (pressure and temperature). A shaped charge produces a jet of dense, typically solid material traveling at very high velocity which penetrates casing, cement, and formation. This penetration process creates a tunnel in the rock connecting the reservoir and the wellbore. Stress waves generated during penetration damage the rock around the tunnel, creating a complex zone of mechanically deformed rock material. Explosive and metallic debris may mix with damaged rock material. Depending on the specific conditions (mechanical rock properties, permeability, fluid viscosities, interfacial tensions, pressures and fluid storage volumes), reverse surge flow following the jet penetration partially or completely clears the tunnel of the charge and rock debris. The resulting tunnel is a rugose, tapered cylinder roughly characterized by its diameter and total depth of penetration. The degree of cleanup and total depth of penetration are two of the most critical parameters influencing flow performance of a perforated well. This work focuses on predicting penetration depth and providing a summary of recent progress and advances in this area. A review of industry penetration prediction methods is presented, including relationships based on surface perforation tests in concrete targets, as well as correlations of penetration depth with properties that could be measured by downhole logging tools. Despite a variety of available methods and published experimental data, penetration depth results are often inconsistent with each other and of questionable use in predicting actual downhole penetration. Moreover, most studies have concentrated on the influence of a single penetration variable. There have been no systematic studies of the interaction of parameters on perforation penetration. This paper emphasizes the critical need for such a study, given the difficulty of downhole measurements of penetration depth to finally achieve reliable penetration predictions, and suggests future directions and conditions necessary for such a study.