The rock mass thermal excitation is performed by means of pumping the flush fluid through the wellbore using a tubing string, the flush fluid temperature differs from the rock mass temperature. Before the thermal excitation, during the thermal excitation and after the termination thereof differential electrical signals proportional to the well bore temperature difference are registered by at least one pair of the temperature transducers positioned along the wellbore axis. The distances between the transducers in the pairs and the number of pairs is selected in advance based on the required accuracy of the determination of the rock mass areas with different properties, minimum and maximum possible length of the rock mass areas identified and the nature and degree of the wellbore temperature noise. Differential electrical signals of the temperature transducers measured before the rock mass excitation start are compared with the differential electrical signals from the same temperature transducers measured during the thermal excitation and the differential electrical signals of different temperature transducers positioned along the wellbore are compared with one another. Based on the comparison results of the differential electrical signals the difference of different rock mass areas are characterized by their properties and the boundaries between the rock mass areas with different properties are identified.