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Salt structures are highly associated with economic hydrocarbon reservoirs. However, drilling a wellbore near or through the salt is usually difficult because the near-salt stresses and pore fluid pressures are largely perturbed due to weaker mechanical strength of salt bodies than their surrounding sediments. We have developed a 2D plane-strain poroelastic finite-element model to simulate stresses and pore pressures in the horizontal-compression salt tectonic system, the Kuqa depression in the Tarim Basin, China, and we use the model results of stresses and pore pressures to calculate safe drilling mud weights on drilling in the salt basin. We found that in early stage of the transient process (close to the undrained condition), pore fluid overpressure occurs at salt convex due to additional compression, whereas underpressure occurs at salt concave due to additional extension within the minibasin. Horizontal effective stress decreases at salt concave (within the minibasin) but increases at salt convex; vertical effective stress varies oppositely to horizontal effective stress. In the final stage of the transient process (drained condition), overpressure has dissipated and pore pressure remains hydrostatic, and stress perturbations are similar to those from the static geomechanical model with elastic sediments: horizontal stress increases at salt convex but decreases at salt concave; vertical stress slightly increases at salt convex and concave. Our calculated safe drilling mud weights and their windows vary over time. Especially at the salt convex, the safe windows are relatively narrow in the early stage of the transient process but become wider in later stage because overpressure dissipates over time and this makes drilling easier. Our results indicate different perturbation patterns of stresses and pore pressures near different salt geometries in a horizontal-compression salt tectonic system, and provide insights into wellbore drilling design and safe drilling mud weights in the salt system.

It has been recognized that stress perturbations in sediments induced by salt bodies can cause elastic-wave velocity (seismic velocity) changes and seismic anisotropy through changing their elastic parameters, thus leading to difficulties in salt imaging. To investigate seismic velocity changes and seismic anisotropy by near-salt stress perturbations and their impacts on salt imaging, taking the Kuqa depression as an example, we have applied a 2D plane-strain static geomechanical finite-element model to simulate stress perturbations and calculate the associated seismic velocity changes and seismic anisotropy; then we used the reverse time migration and imaging method to image the salt structure by excluding and including the stress-induced seismic velocity changes. Our model results indicate that near-salt stresses are largely perturbed due to salt stress relaxation, and the stress perturbations lead to significant changes of the seismic velocities and seismic anisotropy near the salt structure: The maximum seismic velocity changes can reach approximately 20% and the maximum seismic anisotropy can reach approximately 10%. The significant changes of seismic velocities due to stress perturbations largely impact salt imaging: The salt imaging is unclear, distorted, or even failed if we exclude near-salt seismic velocity changes from the preliminary velocity structure, but the salt can be better imaged if the preliminary velocity structure is modified by near-salt seismic velocity changes. We find that the locations where salt imaging tends to fail usually occur where large seismic velocity changes happen, and these locations are clearly related to the geometric characteristics of salt bodies. To accurately image the salt, people need to integrate results of geomechanical models and stress-induced seismic velocity changes into the imaging approach. The results provide petroleum geologists with scientific insights into the link between near-salt stress perturbations and their induced seismic velocity changes and help exploration geophysicists build better seismic velocity models in salt basins and image salt accurately.

We simulated the stress changes around a salt basin using a static salt structure model under compressive stress background to investigate the stress perturbation caused by different salt body shapes and amplitudes. We designed a two-layer salt model with three bulges and sags using finite element methods to calculate the stress perturbation around the salt. The results show that salt shape is closely related to the stress perturbation in the sediments around the salt, and the fluctuations of the bulge and sag (smooth or steep) can also affect the stress perturbation magnitude. Extrusion horizontal stress, normal stress, and out-of-plane stress on the plane would occur near the salt uplift in a compressive tectonic stress environment. In contrast, tensile horizontal stress, out-of-plane stress, and vertical stress would occur near the salt sag. In addition, smoother bulges are associated with smaller produced stress perturbations, and steeper sags are associated with a greater reduction of stress perturbation in the sediment. The stress of a salt structure in western Kelasu of the Kuqa depression was simulated and the applicability of previous conclusions regarding this structure was verified. These conclusions provide scientific basis for the prediction of stress perturbations around salt basin systems. Key words: numerical simulation, salt structure, stress perturbation, Kuqa depression, oil drilling

The analysis of seismic hazards relies on the statistical analysis of historical seismic data and the instrumental seismic catalog to obtain the regional earthquake recurrence interval and earthquake probability. The accuracy of analysis thus depends strongly on the completeness of the seismic data used. However, available seismic catalogs are too short or incomplete for the reliable analysis of the statistical characteristics of earthquakes. If a long-term synthetic seismic catalog can be generated using a physics-based numerical simulation, and the simulation results match the crustal deformation, seismicity, and other observations, then such a synthetic catalog helps us to further understand the characteristics of seismic activity and analyze the regional seismic hazard. In this paper, taking the northeastern Tibetan Plateau as a case study, we establish a three-dimensional visco-elastoplastic finite-element model to simulate earthquake cycles and the spatiotemporal evolution of earthquakes on the model fault system and obtain a seismic catalog on a time scale of tens of thousands of years. On the basis that the model satisfies the regional geodynamics of the northeastern Tibetan Plateau, we analyze seismicity on the northeastern Tibetan Plateau using the simulated synthetic earthquake catalog. The characteristics of earthquake recurrence at different locations and different magnitudes, and the long-term average probability of earthquake occurrence within the fault system on the northeastern Tibetan plateau are studied. The results are a reference for regional seismic hazard assessment and provide a basis for the physics-based numerical prediction of earthquakes.

Drilling into and around salt bodies can present different kinds of geohazards, such as shrinkage or stuck and crushed casings, resulting in well abandonment and huge economic losses. These engineering disasters are more likely to happen when ignoring the stress perturbations caused by the geomechanical interactions between the salt and surrounding sediments. For a better understanding of the stress perturbations, we use a commercial finite-element software, Abaqus, to build a 2D plane-strain finite-element model of the salt structure of Kuqa depression in the Tarim Basin and simulate the stress perturbations around the salt body in the environment of tectonic compression. By analyzing the patterns of stress perturbations due to different salt geometries such as concave and convex salt, we have come to the conclusion that the convex salt causes compressional stresses on the horizontal and out-of-plane directions but the extensional stress on the vertical direction. On the contrary, the concave salt induces extensional stresses on the horizontal and out-of-plane directions but compressional stress on the vertical direction. The results of stress perturbations near a salt structure in the environment of compressional tectonic stress are opposite to those in the environment of extensional tectonic stress, such as the Mad Dog, in the deepwater northern Gulf of Mexico. The shear stress ([Formula: see text]) near the salt structure is bigger than those far away from the salt structure, but is much smaller when compared with horizontal, vertical, and out-of-plane stresses ([Formula: see text]) in the profile, in the salt body, horizontal stress drops and converges to vertical stress and von Mises stress ([Formula: see text]) equals to zero due to isotropic stresses. The results provide scientific insights on stress perturbations and wellbore drilling design near salt structures in the Tarim Basin.

Traditional methods for imaging salt bodies seldom consider near-salt stress perturbations caused by salt, and the associated velocity perturbations of seismic waves in the sediments near the salt. To demonstrate the importance of stress changes caused by the salt on accurately imaging salt bodies, in this study we develop and apply a combined method of geomechanical stress modelling and salt imaging. We simulate the stress perturbations in sediments induced by a salt sphere using a static geomechanical model, and calculate the associated velocity changes of seismic waves in the sediments by using our model stress perturbations. We use the reverse time migration and imaging method to image the salt sphere, and then analyse the imaging results of two cases including and excluding the effects of stress perturbations by the salt sphere on velocity changes of seismic waves. The results show that the near-salt velocity changes of seismic waves induced by stress perturbations near salt bodies can have a significant impact on the salt imaging. We find that when the effects of near-salt stress perturbations are ignored, the imaging of the salt sphere is clearly distorted: the salt sphere is extended vertically and becomes a salt ellipse with a vertical major axis. In contrast, when we include the effects of near-salt stress perturbations, the imaging of this salt sphere accurately matches the salt geometry and position. Thus, the near-salt stress perturbations should not be ignored in salt imaging. This study provides scientific insights for petroleum geologists and exploration geophysicists on the relationship between near-salt stress perturbations and accurate imaging of salt structures.

A compact plasmonic waveguide-coupled resonator system, which consists of a metal–insulator–metal (MIM) waveguide with a double stub side-coupled to a ring cavity, is designed and numerically investigated using finite element method (FEM). Simulation results show that dual Fano resonances with sharp asymmetric line shape are observed in the transmission spectrum. One of the Fano resonances originates from the coupled-resonator effect of the two stub cavities, whereas the other is induced by the ring resonator. The two resonance peaks exhibit different dependencies on the parameters of the structure because of varying mechanisms and can be easily tuned. Moreover, the maximum refractive index sensitivity and Q-factor of the proposed structure are 1000 nm/refractive index unit (RIU) and 41, respectively. The maximum figure-of-merit (FOM ∗ ) is approximately 4200 at 0.71 μ m, which is due to the sharp asymmetric Fano line shape with an ultra-low transmittance at this wavelength. The proposed structure is expected to provide guidelines for the design of nano-sensors.

Longitudinal waves have important applications in modern scientific research and production, as a special acoustic wave, longitudinal waves have a sound transmission performance in negative refractive index materials. This paper has designed a new structure for negative refractive index materials by virtue of COMSOL software and conducted related simulation analysis. Experimental results illustrated that the structure designed had good acoustic longitudinal wave transmission performance. Besides, the effect of sound wave focusing could be achieved by a combination of existing test methods. The design proposed could break the limitation of previous structures on acoustic longitudinal wave transmission. This study is expected to have important implications for the development of solid metamaterial structures.

Well dispersed core/shell structure Fe nanopowders (FeNPs) produced by high energy ion beam evaporation (HEIBE) are added to polyacrylonitrile/N, N-Dimethylformamide (PAN/DMF) solution containing vegetable oil to prepare Fe/C porous nanofibers (FeCPNFs) by electrospinning as electromagnetic microwave absorption material. The FeCPNFs have 3D cross-linked network structure with low graphitization degree. The permittivity and permeability behaviors of the composites made from FeCPNFs and wax are studied in the frequency range of 2.00–18.00 GHz. Mainly due to impedance matching, electric loss, magnetic loss, attenuation constant and “geometrical effect” the FeCPNFs have good microwave absorption properties. The reflection loss (RL) of FeCPNFs can reach − 56.6 dB at matching frequency (4.96 GHz) and matching thickness (4.29 mm). The RL value can also reach −26.1 dB at 11.68 GHz, and effective absorption bandwidth (RL ≤ − 10.0 dB) is 3.00 GHz with a thickness of 2.00 mm. Moreover, under the matching frequency and matching thickness a good absorption performance (RL ≤ − 15.0 dB) from 2.00 GHz to 18.00 GHz is obtained.

This paper focuses on robust output tracking control for quadrotors exposed to parametric uncertainties and external disturbances. Based on the back-stepping control principle, the quadrotor dynamics is decomposed into translational and rotational subsystems. To handle the limitation of traditional extended state observer that can only be effective for integral-chain systems, a high-order extended state observer with special structure is developed to estimate the unmeasurable states and the lumped disturbances in rotational subsystem simultaneously. To avoid the tedious analysis and repeated differentiation of virtual control laws in the back-stepping technique, a first-order sliding mode differentiator is introduced to compute the derivative of virtual control law at each step in the presence of disturbances. The stability analysis is established using the Lyapunov theory. Simulation results demonstrate the effectiveness of the proposed control scheme in achieving a guaranteed tracking performance with respect to an 8-shaped reference trajectory.

Mono-dispersed, spherical and core/shell structure aluminum nanopowders (ANPs) were produced massively by high energy ion beam evaporation (HEIBE). And the number weighted average particle size of the ANPs is 98.9 nm, with an alumina shell (3–5 nm). Benefiting from the passivation treatment, the friction, impact and electrostatic spark sensitivity of the ANPs are almost equivalent to those of aluminum micro powders. The result of TG-DSC indicates the active aluminum content of ANPs is 87.14%, the enthalpy release value is 20.37 kJ/g, the specific heat release S1/Δm1* (392–611 °C) which determined the ability of energy release is 19.95 kJ/g. And the value of S1/Δm1* is the highest compared with ANPs produced by other physical methods. Besides, the ANPs perfectly compatible with hydroxyl-terminated polybutadiene (HTPB), 3 wt. % of ANPs were used in HTPB propellant replaced micron aluminum powders, and improved the burning rate in the 3–12 MPa pressure range and reduced the pressure exponential by more than 31% in the 3–16 MPa pressure range. The production technology of ANPs with excellent properties will greatly promote the application of ANPs in the field of energetic materials such as propellant, explosive and pyrotechnics.

The Jinding Zn-Pb deposit has been generally considered to have formed from circulating basinal fluids in a relatively passive way, with fluid flow being controlled by structures and sedimentary facies, similar to many other sediments-hosted base metal deposits. However, several recent studies have revealed the presence of sand injection structures, intrusive breccias, and hydraulic fractures in the open pit of the Jinding deposit and suggested that the deposit was formed from explosive release of overpressured fluids. This study reports new observations of fluid overpressure-related structures from underground workings (Paomaping and Fengzishan), which show clearer crosscutting relationships than in the open pit. The observed structures include: 1) sand (±rock fragment) dikes injecting into fractures in solidified rocks; 2) sand (±rock fragment) bodies intruding into unconsolidated or semi-consolidated sediments; 3) disintegrated semi-consolidated sand bodies; and 4) veins and breccias formed from hydraulic fracturing of solidified rocks followed by cementation of hydrothermal minerals. The development of ore minerals (sphalerite) in the cement of the various clastic injection and hydraulic fractures indicate that these structures were formed at the same time as mineralization. The development of hydraulic fractures and breccias with random orientation indicates small differential stress during mineralization, which is different from the stress field with strong horizontal shortening prior to mineralization. Fluid flow velocity may have been up to more than 11 m/s based on calculations from the size of the fragments in the clastic dikes. The clastic injection and hydraulic fracturing structures are interpreted to have formed from explosive release of overpressured fluids, which may have been related to either magmatic intrusions at depth or seismic activities that episodically tapped an overpressured fluid reservoir. Because the clastic injection and hydraulic structures are genetically linked with the mineralizing fluid source, they can be used as a guide for mineral exploration.