Summary This paper presents a method to measure porosity and permeability alteration of the porosity and permeability alteration of the crushed-zone using scanning electron microscopy (SEM) and image analysis. A new phenomenon, shock metamorphism, was shown phenomenon, shock metamorphism, was shown to exist and is believed to be useful to evaluate shock wave penetration. Berea sandstone samples were prepared using a modification of the older API-43 recommended practice for test sample preparation. Samples were perforated preparation. Samples were perforated using low and medium penetration shaped charges. Analysis of the low charge shot sample indicated an average porosity reduction of 25%, and an average permeability reduction of 55% within the permeability reduction of 55% within the crushed zone. The sample shot with the medium penetration shaped charge showed planar element shock metamorphism.
Introduction Shaped charge jet perforation is the most widely used method of establishing flow pathways from an oil or gas formation to the inside of a wellbore in oil and gas producing wells. A primary objective of producing wells. A primary objective of the jet perforation process is to create "clean" regularly shaped holes or tunnels that have a high fluid flow capacity. In shaped charge jet perforation, the detonation of an explosive charge containing a conical depression creates a sharply focused intense pressure pulse that can exceed 4 × 10(6) psi. and have a velocity of 30,000 ft/second. This pulse of hot explosion gas pushes aside all materials in its way. As effective as this process is in creating a hole or tunnel, it also alters the rock formation around the 1/4 to 1/2 inch diameter tunnel which is created, as indicated by Bell. This "altered" or "compacted" or "crushed-zone" is believed to be responsible for permeability of this zone being significantly less (up to 70% less) than virgin formation. Several authors have noted the presence of this crushed zone and also studied the effect of the compacted zone on well productivity both experimentally and productivity both experimentally and theoretically. However, their results were not based on direct measurements on the crushed zone. Bell indicated that formation strength, explosive charge shape, charge size, and operating configuration in the wellbore are known to affect shot penetration. But the effect of each of penetration. But the effect of each of these variables on the nature and extent of the crushed zone has not been reported, probably in large part due to lack of an probably in large part due to lack of an experimental methodology to directly observe the crushed zone.