Geophysical Journal | 2002 volume 24 2

Physical properties of rocks of the Kryvoy Rog ultradeep borehole (Ukraine) in different thermobaric conditions

© T.S. Lebedev, V.A. Korchin, V.I. Shapoval, S.I. Shepel, B.Y. Savenko, P.A. Burtny

The results of a set of long-term experimental petrophysical PT-studies of collections of representative samples of the core of the Krivoy Rog ultradeep borehole (KUDB) (specially taken in drilling process) that were made by the authors in the Earth Substance Physical Department of the Institute of Geophysics NAS of Ukraine (Kiev) are briefly summarized. The elastic, electrical, thermal and magnetic parameters of KUDB rocks were studied in strictly oriented structural-textural directions. The experiments were made in specialized high pressure and temperature chambers in which different deep thermobaric condition were simulated in experiments. The differentiation of rocks by their elastic properties along the borehole shaft associated with the peculiarities of their mineral composition and elastic anisotropy in the respective PT-conditions and different stress state has been established. The anisotropy of the distribution of physical parameters of mineral formations detected along the KUDB section is preserved for most of them even at rather great depths. The detected thermobaric dependencies of the specific electrical resistance and the dielectric constant of rocks are due to the degree of their saturation with fluids, the mineralization of the latter, dissociation and dehydration of carbonates, micas and other minerals. With pressure growth, the thermal conductivity and thermal diffusivity coefficients of rocks increase rather notably. They decrease nearly so with temperature growth. Petromagnetic thermobaric experiments also enabled us to establish the anomalous changes of the remanent saturation magnetization and the features of the magnetic anisotropy of some mineral formations of the KUDB. A method of the use of the PT-data on the change of the elastic anisotropy of rocks to foresee possible distructions of the near-shaft space due to the violation of the lithostatic balance of the geologic medium has been worked out. The results of the whole complex of the petrophysical PT-experiments and the geologic geophysical information enable us to predict possible changes of the properties, composition and state of rocks at the horizons yet not reached by boring. They will also help us to set up new deep petrophysical and lithological models of the Earth's crust of the Krivoy Rog structure in future.

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