Redistribution of local fracture aperture and flow patterns by acidizing

Abstract Statistical and spatial distributions of apertures may be changed due to chemical dissolution. The chemical dissolution in rocks may result from the passage of acidic water through fractures or acid fracturing treatment. In this study, an acid injection cell was developed to simulate acidizing stimulation into fractures and investigate fractures surfaces etching and aperture evolution due to acidizing. Results showed that initial hydraulic and mechanical apertures and permeability (under zero stress) were increased due to fracture acidizing and a varying range of 2%–12% contact area was observed. Apertures before and after fracture acidizing followed a log-normal distribution and all of statistical moments were increased by acid injection while the calculated coefficient of variance in both arithmetic and logarithmic scales was decreased after acidizing. Correlation length increased in the direction of acid flow ( x -direction) after acidizing. Results of fluid flow modeling using a developed finite element code showed a channeling path in the x -direction. Furthermore, using fast sequential simulation algorithm, apertures with various spatial correlation length in x and y directions were generated. Numerical modeling results of these generated aperture patterns showed that flow channelizing was increased by increasing of correlation length in the x -direction. Fluid flow rate was increased with increasing of correlation length in x -direction, while it decreased with increasing correlation length in y -direction.