| This research reveals new information on the degree of porosity and permeability alteration of the crushed-zone formed during jet perforation. A relatively new phenomenon, shock metamorphis, is shown to exist in formations containing quartz that are perforated with medium or high penetration charges. Berea sandstone samples 2 by 2 by 20 in. were prepared using a modification of the older API RP 43 recommended practice for test sample preparation. Samples were perforated using low and medium penetration shaped charges. Scanning electron microscopy (SEM), and image analysis have been used to determine porosity and specific surface of both perforated and unperforated samples. Backscattered electron microscopy was employed to determine the extent of the compacted or crushed zone. Analysis was performed both radially, away from the shot center, and longitudinally, along the perforation tunnel. Equations relating specific surface, porosity, and permeability were used to calculate permeability of all samples. A polarizing microscope was used for detection of the degree of shock metamorphism on quartz within the crushed-zone area.; Porosity and permeability obtained from image analysis of the unshot sample were within 1% and 11% respectively of the porosity and permeability of unshot Berea sandstone obtained by conventional core analysis. A similar analysis of the shot samples indicates an average porosity reduction of 25%, and an average permeability reduction of 55% within the crushed zone for a 3.5 gr. RDX charge. A low penetration shaped charge (3.5 gr. RDX), showed fractured quartz but no shock metamorphism. However, a medium penetration shaped charge (10.5 gr. RDX), showed planar element shock metamorphism.; Theoretical analysis for this research involved predicting production through a perforated well when perforating leaves no permeability damage, uniform permeability damage, and nonuniform permeability damage around the perforation tunnel. Results indicated that productivity of a perforated well depends upon the profile of permeability values around the perforation tunnel. A 60% productivity reduction was obtained corresponding to a 55% reduction in permeability around the perforation tunnel. |
