Correlating Particle Size Distribution in a Crushed Zone to Perforating Permeability Damage and Modeling Using Fragmentation Fractal Theory

摘要

Conventional oilfield shaped charges form a jet consisting ofrnhypervelocity metallic particles, whose pressure pulse canrnexceed 4 x 106 psi. When the metallic jet hits the rock target,rnthe resulting shock forms a path of mechanically deformedrnrock as a tunnel. The shock wave also alters the rock massrnaround the tunnel by fragmenting rock and mineral grains.rnThis is phenomena is an important issue in shaped-chargernperforating due to its potential effect on decreasing thernpermeability of the rock surrounding the tunnel and decreasingrnthe efficiency of costly perforating job. Although operatingrnparameters can be set to remove fragmented sand grainsrn(underbalanced perforating), it is practically difficult tornremove all of them to regain the decreased permeability.rnDetermination of permeability and the thickness ofrncrushed zone around perforation tunnel are important forrnproductivity calculations and especially for near-wellborernmodeling. Although productivity of a well after perforating isrna good indication of the permeability damage due tornperforating, it does not give the permeability distribution at thernvicinity of the tunnel. Even in the laboratory shots performedrnunder insitu pressure conditions, it is a difficult task to maprnthe permeability distribution around the tunnel.rnThis paper proposes an easier way to estimate thernpermeability distribution in the crushed zone by modeling therndistribution of grain fragments using fragmentation fractalrntheory. The resulting Eq. describes the permeability by arnfractal model. It calculates pore size distribution from particlernsize data by setting up a hierarchical scaling concept forrnfragmentation to calculate the porosity of incompletelyrnfragmented fractal porous medium. Estimated permeabilitiesrnwere compared against the permeability distribution measuredrnby using pressure transient analysis and computerizedrntomography (CT) scanning during injection test. It was seenrnthat the values are close to each other.