Sound-transparent anisotropic media for backscattering-immune wave manipulation

The scattering behavior of the anisotropic acoustic medium is analyzed to reveal the possibility of routing acoustic signals through the anisotropic layers with no backscattering loss. The sound-transparent effect of such medium is achieved by independently modulating the anisotropic effective acoustic parameters in a specific order, and experimentally observed in a bending waveguide by arranging the subwavelength structures in the bending part according to transformation acoustics. With the properly designed filling structures, the original distorted acoustic field in the bending waveguide is restored as if the wave travels along a straight path. The transmitted acoustic signal is maintained nearly the same as the incident modulated Gaussian pulse. The proposed schemes and the supporting results could be instructive for further acoustic manipulations such as wave steering, cloaking and beam splitting.

Paradigm Shift in Drilling to Completion in Unconventional Reservoir, Eastern Onshore, India

Permo-Triassic formations in Mandapetta field from eastern onshore, India possesses historical drilling challenges in terms of wellbore instability, non-productive time and poor hole condition in deep higher stressed formations. Lack of acquiring reliable log data and problems in recovering good quality cores present difficulties in proper formation evaluation and zone selection for testing. Historical well test results in target K-Formation has been not encouraging despite good gas shows during drilling. Estimated formation pressure gradient ranges 1.45sg-1.52sg. Layered shale with coal and tight sandstone in same open hole section pose risks of mud losses and poor cement job. Present study highlights the workflow adopted to improve drilling and completion in open hole section of more than 1000 m with varying lithology being drilled successfully. Advanced 3D anisotropic acoustic measurements acquired are used to estimate anisotropic elastic properties (vertical and horizontal Young's modulus and Poisson's ratio) in the overlying shales. Horizontal tectonics has been determined across stress induced anisotropic layers. This approach provides better understanding of formations and stress distribution. Thomsen Gamma values range 0.1 to 0.4 in shale layers of overburden formations. In order to minimize uncertainty in 8.5inch section while drilling, advanced logs were acquired in 12.25inch hole section to estimate tectonics at well location while constraining ratio of horizontal to vertical Young's modulus and Poisson Ratio in shale layers based on Thomsen Gamma and clay volume. Analysis suggested typical VTI anisotropy of 15%-20% in shale layers. Inverted direct horizontal strain parameters at well location suggested the ratio of maximum to minimum horizontal stress to vary 1.15-1.23. Mud weight used while drilling 8.5inch section ranged 1.49sg1.52sg against the recommended mud weight of 1.50sg-1.52sg while pumping sealing agents to prevent mud losses in coal layers. Flow rate was maintained on lower values to minimize ECD values. Hole condition improved significantly with no issues in logging. Post-drill anisotropic rock mechanics model suggested good quality sandstone in target source formation with usual conventional reservoir in shallower formation. Zone was selected based on permeability, breakdown and completion quality for perforations. Analysis of high-quality sonic slowness helped to identify possible gas reservoir in laminated source rock. There was stress contrast of 2000psi-2500psi among reservoir layers and shale stress barriers. Implemented workflow and successful execution helped to drill the well 5 days earlier than plan with no major drilling incidents. Successful core recovery for Shale Gas evaluation was also possible due to better wellbore quality. Initial testing of K-Formation produced gas with significant improved flow rate by 150% without any stimulation for the 1st time in the history of the field.

Approaches for investigation of oriented cracks of reservoirs using multicomponent VSP

The paper analyses the VSP data inversion in order to determine elastic constants of a transversely isotropic medium with a horizontal axis of symmetry of an infinite order (HTI), simulating an oriented fractured reservoir. Acquisition system of VSP is characterized by the absence of sub-horizontal directions of propagation of seismic waves. In this regard, it was necessary to determine the accuracy with which the elastic constants of the anisotropic layer are restored. The seismograms of the full wave field were selected as the initial data, calculated synthetically for the model of the medium containing azimuthally anisotropic layers. A complex of compressional and shear waves propagating from a source and recorded in the well. In such layers, the shear wave incident on the roof of the HTI layer splits into two waves that propagate at different velocities and have a mutually orthogonal displacement vectors. The processing task was to select waves S 1 and S 2 and build their arrival time curves. These arrival time curves were used in the inversion. The inversion was solved in the form of minimizing the functional of the mean square residual. Elastic constants, determined by inversion, almost exactly coincided with the model ones. The results obtained show the validity of the chosen approach for solving the inverse problem.

Advanced Formation Evaluation Approaches in Complex Low-Resistivity Thin Shale Sand Laminations: Success Case Histories from Western Ukraine

Several gas fields from the Carpathian Foredeep basin are characterized by high heterogeneity of rock quality. It is critical to understand the characteristics of pore architecture and mineralogy to quantify the rock's storage capacity and productivity. Field "A" is characterized by thin low-resistivity shale-sand laminations, which poses technical challenges to conventional evaluation methods. Until recently, only conventional local logging suites were deployed, and cutoffs-based interpretation was applied. Core analysis was not done. The Ukrainian segment of the Carpathian fold belt and foredeep is located in the westernmost part of the country, bordering Poland, Slovakia, and Romania. A few fields are situated in the foreland basin but most of the production comes from the fold belt, where complex structural traps are in a series of nappe units. Many of the fields were found based on an understanding of the surface geology alone. The presence of anisotropic layers with a predominance of very thin beds and intercalation of shale, siltstone, and sands with low resistivity contrast between water and gas significantly affects the definition of the reservoir properties and potential. Recently, the use of modern logs was mandated to obtain reliable information. In this study, we analyze and discuss the applicability and results of using advanced technology and tailored logs interpretation methods adapted for the local conditions. These methods were applied in different cases in 2019-2021 and enabled building the first robust petrophysical model for these types of reservoirs. Tri-axial resistivity measurements combined with high resolution density and neutron porosity logs optimally defined the porosity and saturations within the thin bedded sequences. Water volumes and textural parameters were computed from dielectric dispersion measurements. Pores system's heterogeneity and grain sorting, free fluid content and downhole testing optimization was performed using high-resolution nuclear magnetic resonance logs. The ability to measure formation pressure in the thin layers help understanding connectivity and deliverability of the reservoirs. The integration of these log measurements enabled unlocking the true properties of the anisotropic layers and quantify the hydrocarbons in place. High-definition borehole imager and dipole sonic logs complemented the petrophysical logs analysis and assisted the geomechanics and geophysics modeling. The addition of pulsed neutron spectroscopy logging further reduced the evaluation uncertainties providing an independent assessment of gas presence and proper control on mineralogy and matrix effects on the log responses to further refine the computation of total and effective porosity, and volumes within the thin sands. Finally, accurate reservoir summations were calculated and used together with producibility estimates and rock mechanical properties to guide the completion and production strategy. This paper presents examples of fit-to-purpose evaluation programs being deployed in such complex scenarios. In addition, it describes key information used to define a future field development management strategy and to optimize the petrophysical analysis. A comprehensive evaluation program and logs analysis can also be used as data calibration for other offset wells and nearby fields with similar properties and evaluation challenges.

Dissipative properties of composite structures. 1. Statement of problem

Object and purpose of research. The object under study is a sandwich plate with two rigid anisotropic layers and a filler of soft isotropic viscoelastic polymer. Each rigid layer is an anisotropic structure formed by a finite number of orthotropic viscoelastic composite plies of arbitrary orientation. The purpose is to develop a mathematical model of sandwich plate. Materials and methods. The mathematical model of sandwich plate decaying oscillations is based on Hamilton variational principle, Bolotin’s theory of multilayer structures, improved theory of the first order plates (Reissner-Mindlin theory), complex modulus model and principle of elastic-viscoelastic correspondence in the linear theory of viscoelasticity. In description of physical relations for rigid layers the effects of oscillation frequencies and ambient temperature are considered as negligible, while for the soft viscoelastic polymer layer the temperaturefrequency relation of elastic-dissipative characteristics are taken into account based on experimentally obtained generalized curves. Main results. Minimization of the Hamilton functional makes it possible to reduce the problem of decaying oscillations of anisotropic sandwich plate to the algebraic problem of complex eigenvalues. As a specific case of the general problem, the equations of decaying longitudinal and transversal oscillations are obtained for the globally orthotropic sandwich rod by neglecting deformations of middle surfaces of rigid layers in one of the sandwich plate rigid layer axes directions. Conclusions. The paper will be followed by description of a numerical method used to solve the problem of decaying oscillations of anisotropic sandwich plate, estimations of its convergence and reliability are given, as well as the results of numerical experiments are presented.

Resolving Seismic Anisotropy of the Lithosphere–Asthenosphere in the Central/Eastern Alps Beneath the SWATH-D Network

The Alpine orogeny is characterized by tectonic sequences of subduction and collision accompanied by break-off events and possibly preceded by a flip of subduction polarity. The tectonic evolution of the transition to the Eastern Alps has thus been under debate. The dense SWATH-D seismic network as a complementary experiment to the AlpArray seismic network provides unprecedented lateral resolution to address this ongoing discussion. We analyze the shear-wave splitting of this data set including stations of the AlpArray backbone in the region to obtain new insights into the deformation at depth from seismic anisotropy. Previous studies indicate two-layer anisotropy in the Eastern Alps. This is supported by the azimuthal pattern of the measured fast axis direction across all analyzed stations. However, the temporary character of the deployment requires a joint analysis of multiple stations to increase the number of events adding complementary information of the anisotropic properties of the mantle. We, therefore, perform a cluster analysis based on a correlation of energy tensors between all stations. The energy tensors are assembled from the remaining transverse energy after the trial correction of the splitting effect from two consecutive anisotropic layers. This leads to two main groups of different two-layer properties, separated approximately at 13°E. We identify a layer with a constant fast axis direction (measured clockwise with respect to north) of about 60° over the whole area, with a possible dip from west to east. The lower layer in the west shows N–S fast direction and the upper layer in the east shows a fast axis of about 115°. We propose two likely scenarios, both accompanied by a slab break-off in the eastern part. The continuous layer can either be interpreted as frozen-in anisotropy with a lithospheric origin or as an asthenospheric flow evading the retreat of the European slab that would precede the break-off event. In both scenarios, the upper layer in the east is a result of a flow through the gap formed in the slab break-off. The N–S direction can be interpreted as an asthenospheric flow driven by the retreating European slab but might also result from a deep-reaching fault-related anisotropy.

Modeling of oil phase displacement processes in heterogeneous anisotropic reservoirs

Methods of computer modeling of slightly permeable anisotropic oil-bearing layers are needed nowadays because they give us a possibility to obtain a concept on filtration processes near producing and forcing wells in different practical situations and in this way to raise the level of exploitation of such layers significantly. On the other hand, they allow evaluation and taking into account some uncertainties which appear as a result of inefficient information on the structure and properties of the layer outside the wells. In order to investigate the practical aspects of supporting efficiency of oil production in anisotropic heterogeneous low permeable reservoirs on the base of combined finite-element-difference method for solving the non-stationary anisotropic piezoconductivity problem, modeling of distribution of layer pressure was carried out in the vicinity of the production and forcing wells taking into account the anisotropy of the permeability and conditions of the oil phase infiltration on the margins of the examined layer. It has been found that the intensity of filtration process between producing and forcing wells depends essentially on their spacing in both shear-isotropic and anisotropic oil-bearing layers. In addition the effect of oil phase permeability in shear direction dominates over the effect of permeability in axes directions. Starting from the obtained information for the effective exploitation of anisotropic slightly permeable layers we need to locate producing and forcing wells in the areas with relatively low permeability of the layer and especially to avoid the places with presence of shear permeability. It is important to locate the wells in such a way that blocking the oil in the direction of reduced permeability and fast depletion of the layer in the direction of increased permeability would not happen as well as mutual exchange between producing and forcing wells would not stop. While locating the system of specified wells within anisotropic layers of oil deposit it is necessary to conduct a systemic analysis of environmental anisotropy of layers aimed at such a location of these wells which would guarantee the effective dynamics of filtration processes around them. Application of quadratic isoparametric approximation of finite-elemental net of examined area of oil-bearing layer and implicit differential time approximation brings to increase of precision and stability of numerical solution of the problem.

Comparison of Quantitative Morphology of Layered and Arbitrary Patterns: Contrary to Visual Perception, Binary Arbitrary Patterns Are Layered from a Structural Point of View

Patterns found among both living systems, such as fish scales, bones, and tree rings, and non-living systems, such as terrestrial and extraterrestrial dunes, microstructures of alloys, and geological seismic profiles, are comprised of anisotropic layers of different thicknesses and lengths. These layered patterns form a record of internal and external factors that regulate pattern formation in their various systems, making it potentially possible to recognize events in the formation history of these systems. In our previous work, we developed an empirical model (EM) of anisotropic layered patterns using an N-partite graph, denoted as G(N), and a Boolean function to formalize the layer structure. The concept of isotropic and anisotropic layers was presented and described in terms of the G(N) and Boolean function. The central element of the present work is the justification that arbitrary binary patterns are made up of such layers. It has been shown that within the frame of the proposed model, it is the isotropic and anisotropic layers themselves that are the building blocks of binary layered and arbitrary patterns; pixels play no role. This is why the EM can be used to describe the morphological characteristics of such patterns. We present the parameters disorder of layer structure, disorder of layer size, and pattern complexity to describe the degree of deviation of the structure and size of an arbitrary anisotropic pattern being studied from the structure and size of a layered isotropic analog. Experiments with arbitrary patterns, such as regular geometric figures, convex and concave polygons, contour maps, the shape of island coastlines, river meanders, historic texts, and artistic drawings are presented to illustrate the spectrum of problems that it may be possible to solve by applying the EM. The differences and similarities between the proposed and existing morphological characteristics of patterns has been discussed, as well as the pros and cons of the suggested method.

Calculation of the intrinsic thermal radiation of plane-parallel quasi-anisotropic multilayer plates with smooth boundaries

The physical meaning of new algorithms for calculating the intensity of a plane homogeneous monochromatic wave of electromagnetic radiation after passing through a multilayer quasi-anisotropic plane-parallel plate is discussed, taking into account the thermal radiation of the layers. The formula connecting the brightness temperature obtained by a microwave radiometer and the effective temperature of the observed surface is used in remote sensing of the earth's surface [16].In this paper, we develop a mathematical apparatus that allows one to construct algorithms that generalize this formula to an arbitrary number of homogeneous quasi-anisotropic layers of a plane-parallel plate. The solution of the problem is complicated by the need to take into account coherent and incoherent effects in a multilayer plate, as well as by the need to construct an adequate method for identifying the waves and energy fluxes under consideration, by the need to clarify the concept of an ideal radiometer that records the observed microwave radiation. In order to test new algorithms and obtain the first results, the facts obtained earlier [19] by calculating the reflection and transmission coefficients for free ice sheets are reproduced using new algorithms for calculating intensities. For an isotropic ice plate 50 cm thick in the L-range, there is a "transparency window" in the area of observation angles of 30 degrees for both polarizations simultaneously. The influence of ice anisotropy on the effects of bleaching and anti-bleaching and related to the Brewster angle is considered. Additionally, the contribution of the ice's own radiation to the observed brightness temperature was estimated by new methods. The case of an anisotropic ice plate with the same parameters but floating in water is considered. It is shown that a change in the conditions of reflection at the ice-substrate interface can be partially compensated by a change in the ice thickness. To control and evaluate the theoretically possible accumulation of errors in calculations, physical quantities are discussed that are analogous to the components of the Poyting vector and remain constant at the boundaries of the layers. For the considered cases of ice, these values are conserved with high accuracy.