FIELD: physics; geophysics.
SUBSTANCE: present invention relates to geophysics and can be used to determine a volume of clearance surrounding a wellbore to be investigated. The present invention is realised using a logging tool which can be installed on a logging cable, a drill string, or a wired drill pipe. A subsurface formation property is determined when using the logging tool. The subsurface formation property may include: voltage, bulk resistivity, horizontal resistivity, vertical resistivity, porosity, permeability, fluid saturation, NMR relaxation time, borehole size, borehole fluid composition, an MWD parameter, or an LWD parameter. The maximum depth of investigation into the subsurface formation is determined using a model response and a noise level, and the volume of clearance is determined using the determined maximum depth of investigation. The maximum depth of investigation and volume of clearance may be determined even without determining boundary layers.
EFFECT: high accuracy of obtained data.
20 cl, 9 dwg
