Search

Hydraulic fracturing is considered the main stimulation method to develop shale gas reservoirs. Due to its strong heterogeneity, the shale gas formation is typically embedded with geological discontinuities such as bedding planes and natural fractures. Many researchers realized that the interaction between natural fractures and hydraulic fractures plays a crucial role in generating a complex fracture network. In this paper, true tri-axial hydraulic fracturing tests were performed on polymethyl methacrylate (PMMA), on which pre-existing fracture was pre-manufactured to simulate natural fracture. A cohesive model has been developed to verify the results of the experimental tests. The key findings demonstrate that the experimental results agreed well with the numerical simulation outcomes where three main interaction modes were observed: crossing; being arrested by opening the pre-existing fracture; being arrested without dilating the pre-existing fracture. Crossing behavior is more likely to occur with the approaching angle, horizontal stress difference, and injection rate increase. Furthermore, the higher flow rate might assist in reactivating the natural fractures where both sides of the pre-existing fractures were reactivated as the injection rate increased from 5 to 20 mL/min. Additionally, hydraulic fractures show a tendency to extend vertically rather than along the direction of maximum horizontal stress when they are first terminated at the interface. This research may contribute to the field application of hydraulic fracturing in shale gas formation. [ABSTRACT FROM AUTHOR]

High-spin states in 189Pt are populated through the heavy-ion fusion-evaporation reaction176Yb (18O, 5n)189Pt at 87MeV beam energy. An array consisting of 13 HPGe detectors is used in conjunction with the plunger device in CIAE. The lifetimes of two levels in the yrast band are determined by using the recoil distance Doppler shift method. The transition quadrupole moments Qt are extracted. The results show that the state has a much larger Qt value than that of the ground state, whereas the value deceases quickly with spin increasing. This may contribute to the shape driving effect of the quasi-neutron from the i13/2 orbital. [ABSTRACT FROM AUTHOR]

The interaction between an electron and an elastic wave is investigated for HgTe and InAs-GaSb quantum wells. The well-known Bernevig–Hughes–Zhang model, i.e., the 4 × 4 model for a two-dimensional (2D) topological insulator (TI), is extended to include the terms that describe the coupling between the electron and the elastic wave. The influence of this interaction on the transport properties of the 2DTI and of the edge states is discussed. As the electron-like and hole-like carriers interact with the elastic wave differently due to the crystal symmetry of the 2DTI, one may utilize the elastic wave to tune/control the transport property of charge carriers in the 2DTI. The extended 2DTI model also provides the possibility to investigate the backscattering of edge states of a 2DTI more realistically. [ABSTRACT FROM AUTHOR]

Geothermal energy is a kind of renewable, sustainable and clean energy resource. Geothermal energy is abundant in carbonate reservoirs. However, low matrix permeability limits its exploitation. The supercritical carbon dioxide (SC--CO2) jet fracturing is expected to efficiently stimulate the carbonate geothermal reservoirs and achieve the storage of CO2 simultaneously. In this paper, we established a transient seepage and fluid-thermo-mechanical coupled model to analyze the impact performance of SC-CO2 jet fracturing. The mesh-based parallel code coupling interface was employed to couple the fluid and solid domains by exchanging the data through the mesh interface. The physical properties change of SC-CO2 with temperature were considered in the numerical model. Results showed that SC-CO2 jet fracturing is superior to water-jet fracturing with respect to jetting velocity, particle trajectory and penetrability. Besides, stress distribution on the carbonate rock showed that the tensile and shear failure would more easily occur by SC-CO2 jet than that by water jet. Moreover, pressure and temperature control the jet field and seepage field of SC-CO2 simultaneously. Increasing the jet temperature can effectively enhance the impingement effect and seepage process by decreasing the viscosity and density of SC-CO2. The key findings are expected to provide a theoretical basis and design reference for applying SC-CO2 jet fracturing in carbonate geothermal reservoirs. [ABSTRACT FROM AUTHOR]

We investigate the efficiency of electrical manipulation in a two-dimensional topological insulator by inspecting the electronic states of a lateral electrical potential superlattice in the system. The spatial distribution of the electron density in the system can be tuned by changing the strength of the externally applied lateral electrical superlattice potential. This provides us the information about how efficiently one can manipulate the electron motion inside a two-dimensional topological insulator. Such information is important in designing electronic devices, e.g., an electric field effect transistor made of the topological insulator. The electronic states under various conditions are examined carefully. It is found that the dispersion of the mini-band and the electron distribution in the potential well region both display an oscillatory behavior as the potential strength of the lateral superlattice increases. The probability of finding an electron in the potential well region can be larger or smaller than the average as the potential strength varies. These features can be attributed to the coupled multiple-band nature of the topological insulator. In addition, it is also found that these behaviors are not sensitive to the gap parameter of the two-dimensional topological insulator model. Our study suggests that the electron density manipulation via electrical gating in a two-dimensional topological insulator is less effective and more delicate than that in a traditional single-band semiconductor. [ABSTRACT FROM AUTHOR]

Excited states in 106Ag are populated through the heavy-ion fusion evaporation reaction 100Mo(11B,5n)106 Ag at a beam energy of 60 MeV. Lifetimes are measured for transitions of the two negative-parity rotational bands in the nucleus 106 Ag. The reduced transition probabilities show a great difference between the two bands. The staggering of the B(M1) and B(M1)/B(E2) values with spin are not observed. The bands are identified to be built on two distinct quasiparticle configurations. These results are contrary to an earlier suggestion that the pair of bands in 106 Ag are chiral doublet bands. [ABSTRACT FROM AUTHOR]

The chiral doublet bands were claimed to be found in several silver isotopes. In the present study of negative parity bands of the odd-even 103,105,107Ag, by using the principal cranking Nilsson-Strutinsky approach it is demonstrated from the point view of spectroscopy that the nearly degenerate ?I=1 doublet bands could be built on the same configuration with different signature combination of one unpaired proton and two unpaired neutrons. Combining with the small triaxial deformation calculated (ɣ<15°), the existence of chiral rotation in 103,105,107Ag is strongly questioned. In odd-odd 106Ag, the candidate chiral rotational band which possesses much larger moments of inertia than the yrast band, analogously to similar bands observed in 105,107Ag, is assigned to a configuration with two more neutrons in the ?1h11/2 orbitals than its yrast partner. Such assignment will almost double the B(E2) values within the band compared to the yrast band, which is consistent with the primary experimental observation. [ABSTRACT FROM AUTHOR]

Excited states of the odd-odd nucleus 122I are investigated via the fusion-evaporation reaction 116Cd(11B,5n) at a beam energy of 68 MeV. The two most strongly populated bands in 122I are observed up to excitation energies around 10.5 MeV. Their possible configurations at lower spins are assigned to πh11/2 ... vh11/2 and πh11/2 ... vd5/2 based on the observed population, B(M1)/B(E2) values, alignments and signature splitting. E1 transitions are observed connecting the πh11/2 ... vd5/2 band to the πh11/2 ... vh11/2 band, which may be evidence of octupole collectivity. Band terminations caused by the full alignment of the valence nucleons outside the 114Sn core are observed in both bands. [ABSTRACT FROM AUTHOR]

High spin states of the odd-odd nucleus 92Nb are investigated using the 82Se (14N, 4n)92Nb reaction at a beam energy of 54 MeV. The level scheme of the 92Nb was extended up to Jπ =(16+) at about 7.3 MeV and Jπ=(21−) at about 9.7 MeV. According to systematic analyses and a comparison with the neighboring nucleus, the higher spin states could be interpreted by the multi-particle excitations in the π(f5/2,p3/2,p1/2,g9/2)⊗ν(p1/2,g9/2,d5/2, g7/2) configuration space. [ABSTRACT FROM AUTHOR]