Forward modeling of P- and S-waves response of fractures intersected with horizontal wells in tight reservoirs

Horizontal wells play an important role in expanding the drilling volume of reservoirs and oil production area, and are widely used in unconventional reservoirs. Fractures have a positive effect on reservoir permeability, but fractures can also cause accidents such as casing deformation and inter-well frac-hit. It is of great significance to identify and evaluate fractures intersected with horizontal wells in tight reservoirs. In this paper, a three-dimensional numerical model of horizontal wells and fractures in tight reservoirs is designed. The responses of monopole P-wave and dipole S-wave to fractures with different width, dip angle and filling medium are systematically studied, by using three-dimensional finite difference algorithm. The results show that when the fracture is filled with calcite, the amplitude attenuation of monopole P-wave and dipole S-wave has a monotonic exponential increase with the increase of fracture width and the decrease of fracture dip angle. In the real data processing, the amplitude attenuation of P- and S-waves can be used to jointly evaluate the fracture filled with calcite. When the fracture is filled with water, both P- and S-waves have prominent amplitude attenuation. P wave amplitude attenuation does not have a monotonic variation with the increase of fracture width but it has a monotonic increase with the decrease of fracture dip angle. S wave amplitude attenuation has a monotonic increase with the increase of fracture width and the decrease of fracture dip angle. The amplitude attenuation of P- and S- waves rises significantly when the fracture is filled with natural gas. This study is crucial for better understanding the response of P- and S-waves to fractures intersected with borehole in tight reservoirs, and it provides useful information for the inversion of fracture parameters by using P- and S-waves

Characteristics and Origin of Methane Adsorption Capacity of Marine, Transitional, and Lacustrine Shales in Sichuan Basin, China

Adsorbed gas is an important component of shale gas. The methane adsorption capacity of shale determines the composition of shale gas. In this study, the methane adsorption capacity of marine, transitional, and lacustrine shales in the Sichuan Basin was analyzed through its isothermal adsorption, mineral composition, water content, etc. The results show that the methane adsorption capacity of marine (Qiongzhusi Formation and Longmaxi Formation), transitional (Longtan Formation), and lacustrine (Xujiahe Formation and Ziliujing Formation) shales is significantly different. The Longtan Formation has the strongest methane adsorption capacity. This is primarily related to its high organic matter and organic matter type III content. The methane adsorption capacity of the lacustrine shale was the weakest. This is primarily related to the low thermal evolution degree and the high content of water-bearing clay minerals. Smectite has the highest methane adsorption capacity of the clay minerals, due to its crystal structure. The water content has a significant effect on methane adsorption largely because water molecules occupy the adsorption site. Additionally, the temperature and pressure in a specific range significantly affect methane adsorption capacity

Electrically assisted stereolithography 3D printing of graded permittivity composites for in-situ encapsulation of insulated gate bipolar transistors (IGBTs)

Insulated gate bipolar transistors (IGBTs) find applications in diverse fields, such as integrated motor drives, controllable power systems, and electric vehicles. However, traditional IGBT encapsulation materials are unsuitable for high-voltage applications due to the excessive electric field stress generated at the triple junction; an insulation-enhanced encapsulation material is therefore necessary. Here, using an electrically assisted stereolithography (SLA) 3D printing strategy, we fabricate an encapsulation material with graded permittivity that can uniform the electric field stress distribution in IGBTs. Compared with pure resin and uniform-dispersed BaTiO3-resin composite encapsulation, the graded BaTiO3-resin composite reduces the generated maximum electric field stress (Emax) from 190.2 to 108.3 kV/mm (nearly a 50% decrease). Regarding the partial discharge inception voltage, the devices packaged with graded BaTiO3-resin composite (4.07 kV) also performed better than devices packaged with resin (1.96 kV) and uniform-dispersed BaTiO3-resin composite (2.51 kV). This novel electrically assisted SLA 3D printing strategy will open a new window for the in-situ encapsulation of IGBTs and other microelectronics

In Situ Triggering and Dynamically Tracking the Phase Transition in Vanadium Dioxide

As the most widely studied thermochromic material, monoclinic vanadium dioxide (VO₂ (M)) shows promising applications in the energy-saving field. Solid-state transformation, especially fast annealing, plays an important role in the production of VO₂ nanomaterials. On the other hand, the fast process makes it impossible to real-time monitor the phase transition in VO₂. In this paper, a differential scanning calorimetry technique is proposed to in situ trigger and dynamically track the phase transition of VO₂ nanoparticles, which gives a distinguished method to identify the underlying size-dependent and defect-mediated structure phase transition