Joint inversion of high-frequency induction and lateral logging sounding data in earth models with tilted principal axes of the electrical resistivity tensor

In this article, we are the first to formulate the direct and inverse problems of resistivity logging on determining the components of the electrical resistivity tensor of rocks from a set of high-frequency induction and lateral logging sounding measurements. Using a finite element approximation, high-order hierarchical basis functions, computationally efficient multilevel methods and a multistart algorithm with the DFO-LS local optimization method, we investigate the capability of reconstructing the horizontal and vertical resistivity components, as well as the tilt of the resistivity tensor principal axes with regard to the study of complex geological objects. A separate consideration is given to a realistic generalized geoelectric model of the unique hydrocarbon source with hard-to-recover reserves, the Bazhenov Formation.

QERT - Quadrupole Electrical Resistivity Tomography

<p><span>The quadrupole technique for geoelectrics yields the apparent resistivity in a tensorial form in contrast to the scalar apparent resistivity obtained from classical geoelectrics. The quadrupole method in geoelectrics has been applied in the past only for long offsets between transmitter and receiver. We scaled down the method to profile-style and grid-style short offset applications. Analysis of the invariants of the apparent resistivity tensor and its representation as ellipse can be used to obtain an estimate of the dimensionality of the subsurface conductivity distribution. We present the basic theory of the quadrupole ERT technique along with numerical and field examples highlighting the advantages over classic geoelectrical survey methods.<br></span></p>

Магнетотранспортная спектроскопия интерфейсных, квантово-ямных и гибридных состояний в структурах с многочисленными слоями HgTe толщиной 16 нм

The longitudinal and Hall components of the resistivity tensor are measured in structures with multiple HgTe layers 16 nm thick in magnetic fields to 12 T at temperatures from 1.5 to 300 K. The slope of the magnetic-field dependence of the Hall resistance is found to change its sign at a certain critical temperature T _ c = 5 and 10 K in the two studied samples, which indicates the presence of two types of charge carriers and a change in the relation between their contributions to the Hall resistance with temperature. The low critical temperature and manifestation of the “two-component” nature of the Hall curves only at T > T _ c prove that the ground state of the system at T = T _ c is gapless. At higher temperatures (20 K < T < 200 K), the Hall concentration is proportional to the temperature with good accuracy. The description of the charge-carrier dispersion laws by the 8-band kp model taking into account Γ_8-band-edge splitting caused by mechanical stresses, which forms both types of state in HgTe, makes it possible to quantitatively describe the observed magnetotransport features. It is shown that they are associated with the simultaneous filling of electron and hole states formed as a result of mixing interface states responsible for the topological-insulator phase and the quantum-confined states in the Γ_8 band.

The Effects of 3D Electrical Anisotropy on Magnetotelluric Responses: Synthetic Case Studies

Using the staggered-grid finite difference method, a numerical modeling algorithm for a 3D arbitrary anisotropic Earth is implemented based on magnetotelluric (MT) theory. After the validation of this algorithm and comparison with predecessors, it was applied to several qualitative and quantitative analyses containing electrical anisotropy and a simple 3D prism model. It was found that anisotropic parameters for ρ 1 , ρ 2 , and ρ 3 play almost the same role in affecting 3D MT responses as in 1D and 2D without considering three Euler's angles α S , α D , and α L . Significant differences appear between the off-diagonal components of the apparent resistivity tensor and also between the diagonal components in their values and distributing features under the influence of 3D anisotropy, which in turn help to identify whether the MT data are generated from 3D anisotropic earth. Considering the deflecting effects arising from the inconsistency between the anisotropy axes and the measuring axes, some strategies are also provided to estimate the deflecting angles associated with anisotropy strike α S or dip α D , which may be used as initial values for the 3D anisotropy inversion. [Figure: see text]

Anisotropic resistivity tensor of melt-cast Bi2212 superconductors from QTA

Bi2Sr2CaCu2O8+δ HTSC superconductor is characterized by a very strong normal-state resistivity anisotropy, with ρc/ρab typically above 10E4. The aim of this study is to use Quantitative Texture Analysis from x-ray diffraction measurements to estimate the orientation effect on the anisotropic macroscopic resistivity in melt-cast bulk Bi2Sr2CaCu2O8+δ superconductors. Our approach uses the geometric mean [1] of the single crystal resistivity tensor weighted by the Orientation Distribution Function (ODF) to quantitatively estimate the macroscopic resistivity tensor of the samples. The ODF is obtained from x-ray Combined Analysis [2], using the E-WIMV algorithm of the MAUD software. The GMA applies to the rank-two resistivity tensor of the orthorhombic space group considered tetragonal due to the small difference of a- and b-axes of the phase, with only two independent tensor components. We relate a relatively good agreement between measured and calculated macroscopic anisotropic resistivity ratios. Even with ρc/ρab between 10E4 and 10E5 for Bi2212 at room temperature in single crystals [3], we experiment macroscopic ratio in our bulk samples of around only 2. This small ratio is explained by the weak planar- or fiber-like (Figure) texture achieved in the melt-cast samples, characterized by maxima of orientation distributions not larger than 10 mrd. Calculated resistivities, based on homogeneous crystallites, perfect grain boundaries and no secondary phases, are 10 times larger than the observed ones. This suggests that the observed minor phases positively affect conductive pathways between grains. Calculated and measured anisotropic resistive ratios are coherent with one another, and Combined Analysis gives good predictions of these former.