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Flow-induced vibrations (FIVs) are of great interest in various engineering fields. Although FIVs possibly cause some undesirable response and fatigue damage, they can also be used to harvest hydraulic and wind energy. This paper investigated the effects of the attack angle (α) and length ratio (d/D) of a trapezoidal oscillator on the FIV response and energy harvesting capability. The experimental results illustrate the occurrence of a full interaction between the vortex-induced vibration (VIV) and galloping at α = 0° and α = 90°. The attack angle and length ratio greatly influence the energy harvesting. In general, a trapezoidal oscillator at α = 0° exhibits better energy harvesting than that at α = 90°. At α = 0°, the triangular oscillator gains the maximum amplitude of 0.703D with an output voltage of 10.407 V, harvested power of 24.056 mW, and harvesting efficiency of 12.151%. Nevertheless, the performance is reduced as the length ratio increases. At α = 90°, a trapezoidal oscillator with d/D = 0.5 is considered as the best one for energy harvesting. The computational fluid dynamics (CFD) analysis indicates that the displacement is highly related to the transferred energy between the oscillator and the fluid. A greater amount of transferred energy is the main cause of larger displacement, resulting in a more disordered vortex shedding. Finally, it is recommended to install a triangular oscillator at α = 0° to deliver optimal energy harvesting.

The coexistence of blowout and lost circulation in multi-pressure fractured reservoirs has always been a huge challenge to the oil industry. Although the use of high-density kill fluids can ensure the safety of well control, the problem of lost circulation in low pressure layer is still troublesome. Gel is widely used as a temporary plugging system, but the conventional gel plugging system will float when used in combination with high-density kill fluid, resulting in failure of temporary plugging. In this paper, a novel high-density bromide-based nanocomposite gel (HDGEL) was developed, the gel formation mechanism was explored, and its performance was evaluated in the laboratory. The gel is weighted by sodium bromide (NaBr), and cross-linked by covalent bonds, density 1.2–1.5 g/cm3 adjustable, and its temperature resistance can reach 160 °C. Rheological tests show that the gel solution has low initial viscosity and easy to pump. The gelation time can be adjusted from 8 to 12 h, which can be directly broken by the drill or regular jetting nozzle and then flowed back. It can be used in combination with high-density kill fluid to ensure temporary plugging effect. In the fractures with tip sizes (0.014 cm), the maximum bearing pressure of HDGEL is 17.52 MPa, and the regained-permeability recovery can reach 86.81% without the use of gel breaker. This paper introduces a new gel system for multi-pressure reservoirs that can be used in combination with high-density kill fluid and makes recommendations for its engineering application.