METHOD FOR DETERMINING CHANGE OF PROPERTIES IN A NEAR-BOREHOLE ZONE OF A FORMATION DUE TO INVASION OF A DRILLING MUD

摘要

A core sample is taken from a wall of a borehole and at least one core fragment is cut from the core sample. The irradiation of the core fragments is carried out with longitudinal acoustic waves and a propagation velocity of the longitudinal acoustic waves in each of the core fragments is measured. An empirical relationship between a velocity of a longitudinal acoustic wave and a porosity for a given lithological type of the rock is selected. A porosity for each core fragment is determined using the measured velocities of the longitudinal acoustic wave and the selected empirical relationship. A value for porosity change is determined by comparing the determined porosity values for the core fragments and a value of a reference porosity typical for the given lithological type of the rock.