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Results of applying of nonlinear AVAZ inversion optimization algorithm to data from 3D wide-azimuth seismic survey in the Republic of Serbia are presented. The algorithm is based on exact reflection coefficients formulas for PP reflection from anisotropic medium. We compare it with a conventional algorithm based on Ruger linear approximation of P-wave reflection from a boundary between isotropic and anisotropic (HTI) media. Maps of fracture orientation and anisotropy degree are more detailed in the case of using AVAZ inversion based on exact formulas. The results are in general accordance with the FMI well data, which indicates reliable performance of the algorithm.

The paper considers an algorithm for calculating reflection coefficients from boundary between two HTI media. Analysis of the presence of anisotropy above and below the target boundary, as well as variations in the parameters of HTI media, was done. Interpretation of reflection data from the boundary between two HTI media with neglect of anisotropy above or below potentially leads to significant errors in estimation of symmetry axes directions, and hence fracturing orientation. Overestimation/underestimation of an elastic parameter in the overlying HTI medium could lead to a corresponding overestimation/underestimation of similar parameter in the underlying target layer in the result of AVAZ inversion. Furthermore, among the anisotropy parameters Thomsen parameterγhas most significant influence on the reflection coefficients dependences. Thus, the parameterγcould be used foremost as a result of the AVAZ inversion.

This paper presents the acoustic measurements results on synthetic samples containing a system of oriented disc-shaped cracks simulating a fractured medium. An effective model for such media is a model with a transversely isotropic symmetry system under the condition that the host medium is isotropic. FDM 3D printing technology with molten plastic thread was used to form synthetic samples. The results of the recorded acoustic measurements have shown the occurrence of anisotropy of the host medium due to horizontal layering of plastic threads. In the case of printing internal cracks using this technology, the samples contain inhomogeneities due to the greater sintering of plastic threads around the cracks. It was also shown that the use of SLA technology (printing from liquid photopolymer) potentially avoids the indicated effects, but requires developing the technique for printing samples with cracks. Acoustic measurements on the sample without cracks formed by this technique confirmed its isotropy.

Summary The issues of detailed study of target objects of the medium are considered, which are of interest for the processes of exploration and development of oil and gas reservoirs. Consideration is carried out under an example of data preparation for determining the parameters of target fractured objects. It is shown that the use of a set of methods, consisting of ray tracing, 5D interpolation and factor decompositions, made it possible to obtain qualitative data for solving the corresponding inverse problem.

—The paper considers the results of a series of laboratory experiments (more than 100) on the formation of synthetic sand samples containing water/ice and methane or tetrahydrofuran hydrates in the pore space and of the measurement of their acoustic properties (velocities and attenuation of acoustic waves). The main aim of the experiments was to establish the relationship between the velocities of acoustic waves and the ice or hydrate saturation of the samples. An increase in the content of ice and hydrates always leads to a velocity increase. However, the rate of the velocity increase is determined by the localization of ice and hydrates in the samples: at the contacts between the sand grains (“cementing” model) or in the pore space (“filling” model). It has been established that the “cementing” model, characterized by a drastic initial increase in velocities, works for ice or gas hydrates formed from free methane and localized in the pores. On the contrary, tetrahydrofuran hydrates form by the “filling” model and cause a slow increase in velocities.

The results of thermohydraulic code HYDRA-IBRAE/LM/V1 verification on experimental data obtained using the BN-600 reactor in different years are described. The particulars of the computational scheme of the reactor using HYDRA-IBRAE/LM/V1 for modeling the BN-600 operating regime are presented. In preparing the scheme, special attention was devoted to accurate modeling of the reactor cool-down regimes on natural circulation as being most important from the safety validation standpoint. The computational results obtained with the uncertainty of the initial data taken into account are presented for such a cool-down regime.

The system of equations from a two-fluid model is widely used in modeling thermohydraulic processes during accidents in nuclear reactors. The model includes conservation equations governing the balance of mass, momentum, and energy in each phase of the coolant. The features of heat and mass transfer, as well as of mechanical interaction between phases or with the channel wall, are described by a system of closing relations. Properly verified foreign and Russian codes with a comprehensive system of closing relations are available to predict processes in water coolant. As to the sodium coolant, only a few open publications on this subject are known. A complete system of closing relations used in the HYDRA-IBRAE/LM/V1 thermohydraulic code for calculation of sodium boiling in channels of power equipment is presented. The selection of these relations is corroborated on the basis of results of analysis of available publications with an account taken of the processes occurring in liquid sodium. A comparison with approaches outlined in foreign publications is presented. Particular attention has been given to the calculation of the sodium two-phase flow boiling. The flow regime map and a procedure for the calculation of interfacial friction and heat transfer in a sodium flow with account taken of high conductivity of sodium are described in sufficient detail. Correlations are presented for calculation of heat transfer for a single-phase sodium flow, sodium flow boiling, and sodium flow boiling crisis. A method is proposed for prediction of flow boiling crisis initiation.

The basic relations used in the HYDRA-IBRAE/LM/V1 code for calculating the flow and heat-exchange of sodium coolant in fuel-rod assemblies in regimes with and without boiling and in the presence of a crisis of heat exchange are presented. The experimental data suitable for verifying the thermohydraulic code for calculating friction in one- and two-phase regimes as well as heat exchange in regimes with and without boiling are picked on the basis of a review of the literature. The computational error of different parameters is obtained on the basis of the verification results. It is shown that the thermohydraulic code HYDRA-IBRAE/LV/V1 can be used to calculate correctly the primary processes in design basis and beyond-design basis accidents in sodium-cooled reactor facilities.