One of essential attributes of the method of electromagnetic monitoring of geodynamic processes is that under the action of tectonic processes, electrical properties of a geological structure change. Electrical logging data give a large body of information for the study of rocks composing a section of formations of the Earth's crust. Definition of elastic and electrical properties of sedimentary rocks is of geophysical interest. An effective solution of such problems would make it possible to essentially raise the accuracy of interpreting seismic prospecting and other geophysical data. It is noted that a combination of various geophysical methods increases stability and accuracy of the solution of inverse problems.
Interpretation of geophysical data, including the drilling data, allows reconstructing a detailed structure of borehole environment zones and estimating the influence of pollution of a collector with the help of a borehole mud filtrate. Results of the combined geophysical and hydrodynamic interpretation can be used not only in the conventional exploration for oil, evaluation of its reservers and monitoring of oil production, but also for optimization of the technology of development of deposits, perforation of productive intervals and control of technologies of oil handling.
As is known, the major factors defining the electrical conductivity of sedimentary rocks are porosity and mineralization of water-saturated formations. Oil and gas deposits of a terrigenous geological structure are represented by porous collectors, the filled-in with oil and water-saturated formations. When drilling a borehole, a borehole mud filtrate penetrates into a porous space, pushing oil and a water-saturated formation deep down. This process evolves with time, and characteristics of the changed zone depend both on technological parameters of drilling and on hydrophysical features of beds (viscosity of electroconducting fluids, concentration of salts, etc.). The dependence of the electrical conductivity of rocks on their porosity was a subject of some theoretical and experimental surveys. Evidently, Archie was the first to propose an empirical formula resulted from studying the core material
In this paper, formula is obtained with the negative value of the index of consolidation for the case of small values of porosity as a necessary condition of existence of a passage to the limit of the propagation velocity of seismic waves in saturated electroconducting fluid porous media in the Earth's constant magnetic field, to the propagation velocity of seismic waves in elastic media under the same conditions. Also, there is obtained a formula connecting conductivity with the streaming current coefficient, as well as with dielectric permeability of a fluid, zeta potential, porosity, permeability,and with the ratio of the physical density of the conducting fluid to the physical density of a conducting porous body.