A method for determining a fracture aperture of a fracture aperture in a wellbore comprises measuring a resistivity of the wellbore with a downhole tool in a wellbore for obtaining an image of the wellbore. Based on the image, the method detects fractures in the wellbore, and calculates a fracture aperture of the detected fracture according to a predetermined model of the wellbore set up based on hypothesis relative to the configuration of the wellbore. Then, the method estimates a correction to the predetermined model when at least one of the hypothesis is not met, and determines an uncertainty range for the fracture aperture also using a measured parameter.