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China’s natural gas demand is growing under the “dual carbon” goal. However, the peaking capacity of gas storage remains insufficient. Oil reservoir-based underground gas storage (UGS) has, thus, emerged as a critical research focus due to its potential for efficient capacity expansion. The complexity of seepage and phase change characteristics during the multi-cycle injection–production process has not been systematically elucidated. This study combines experimental and numerical simulations to examine the seepage and phase change characteristics. This study innovatively reveals the synergistic mechanism of permeability, pressure, and cycle. The control law of multi-factor coupling on the dynamic peaking capacity of UGS is first expounded. Oil–water mutual drive reduced oil displacement efficiency by 2.5–4.7%. Conversely, oil–gas mutual drive improved oil displacement efficiency by 3.0–4.5% and storage capacity by 4.7–6.5%. The fifth-cycle oil–gas mutual displacement in high-permeability cores (74 mD) under high pressure (22 MPa) exhibited reductions in irreducible water saturation (7.06 percentage points) and residual oil saturation (6.38 percentage points) compared with the first-cycle displacement in low-permeability cores (8.36 mD) under low pressure (16 MPa). Meanwhile, the gas storage capacity increased by 13.44 percentage points, and the displacement efficiency improved by 10.62 percentage points. Multi-cycle huff-and-puff experiments and numerical simulations revealed that post-depletion multi-cycle huff-and-puff operations can enhance the oil recovery factor by 2.74–4.22 percentage points compared to depletion. After five-cycle huff-and-puff, methane content in the produced gas increased from 80.2% to 87.3%, heavy components (C8+) in the remaining oil rose by 2.7%, and the viscosity of the remaining oil increased from 2.0 to 4.6 mPa·s. The deterioration of the physical properties of the remaining oil leads to a reduction in the recovery factor in the cycle stage. This study elucidates seepage mechanisms and phase evolution during multi-cycle injection–production, demonstrating the synergistic optimization of high-permeability reservoirs and high-pressure injection techniques for enhanced gas storage design and efficiency.

Exceptional points pose exceptional difficulties to access and encircle. By simply gating graphene, it is now easier to hit the exceptional point.Exceptional points pose exceptional difficulties to access and encircle. By simply gating graphene, it is now easier to hit the exceptional point.

Injecting liquid into the formation has an impact on the microstructure of the reservoir and formation fluids, and negative effects often lead to the failure of oil well stimulation measures to achieve the expected results. It is crucial to clarify the reasons for the decrease in the injection capability of low-permeability reservoirs in China and the mechanisms of the impact of on-site injection water quality. This study first conducted injection experiments with different water qualities. To study the micro factors that cause damage, clay mineral X-ray diffraction (XRD) analysis, high-pressure mercury injection experiments before and after damage, nuclear magnetic resonance (NMR) during the damage process, scanning electron microscopy (SEM) after damage, and energy dispersive spectroscopy elemental spectrum analysis (EDS) of incompatible sediment were carried out on the experimental core. In injection experiments with different water qualities, the permeability decreased by up to 65.35% when the injection volume reached 60 PV. The main causes of the decrease in injection capability are poor reservoir porosity and permeability and formation particle blockage. The particles mainly come from suspended particles, emulsified oil, migration of formation particles, and sediment formed by the injected water. This paper also proposes a reference for water quality index optimization in similar reservoirs. The new water quality index reduced permeability damage by at least 3.22%.

Carbon Capture, Utilization and Storage (CCUS) technology is one of the most practical means to meet zero greenhouse gas emission goal of the Paris Agreement and to ensure profitability, which could achieve permanent sequestration of CO2. Due to the cost constraints of CCUS implementation, improving recovery and maximizing storage efficiency have become a critical part of ensuring economic efficiency. This research aims to analyze the effects of key factors on enhancing gas recovery and storage efficiency, combined with the validation of CO2 displacement and storage mechanisms. Therefore, long core experiments and different dimensional simulations were established based on R gas reservoir (one of the actual gas reservoirs in Northeast China), which were designed for sensitivity analyses of different influencing parameters and quantitative analyses of different storage mechanisms during CCUS process. When the conditions (temperature and pressure) were closer to the CO2 critical point, when the following parameters (the CO2 purity, the injection rate and the dip angle) became larger, when the reservoir rhythm was reversed and when the irreducible water was is in existence, the final displacement and storage effects became better because of weaker diffusion, stronger gravity segregation and slower CO2 breakthrough. The contributions of different storage mechanisms were quantified: 83.78% CO2 existed as supercritical fluid; 12.67% CO2 was dissolved in brine; and 3.85% CO2 reacted with minerals. Some supercritical and dissolved CO2 would slowly transform to solid precipitation over time. This work could provide theoretical supports for CCUS technology research and references for CCUS field application. At the same time, countries should further improve CCUS subsidy policies and make concerted efforts to promote the globalization and commercialization of CO2 transport.

Metasurfaces excel at local, spatially varying control of wavefronts, whereas photonic crystals (PhCs) are admired for their nonlocal resonances such as bound states in the continuum (BICs). These two regimes—local control and nonlocal collective response—have long been viewed as difficult to integrate within a single platform. Here, we introduce local-nonlocal assisted multifunctional PhCs unifying wavefront shaping and BICs by embedding meta-notches within PhC pillars. The locally tunable notches generate spectral-zero-assisted topological phase for efficient 2π coverage, while the strongly confined BIC modes remain largely unperturbed, preserving high- Q nonlocal resonances. This constructive local-nonlocal integration synthesizes the design freedom of metasurfaces with the dispersive resonance of PhCs in a single planar device. Our approach extends the capabilities of flat optics, enabling multifunctional PhCs and opening pathways toward higher-order topologies, advanced imaging, communication, and analogue optical computing.

For capturing dynamic information about a filled-cave in the fractured reservoir, a novel Pressure Transient Analysis (PTA) analytical model for a well located at the filled-cave is established. In this new model, we consider the stress-sensitivity of the filled-cave and the inter-porosity flow of fracture. First, Perturbation transformation was used to obtain the pressure distribution in the filled-cave zone. Then, the Warren–Root model was applied to establish the pressure solution in the fractured reservoir. Next, the pressure and its derivative are obtained by the Laplace transformation and Steftest inversion. Lastly, the Bottomhole Pressure (BHP) and Bottomhole Pressure Derivative (BHPD) combined curve reveals the flow regimes of this novel model. The results show the composite model can be used to characterize the fractured reservoir with the filled-caves, and its flow follows the composite flow regimes. The spherical flow has an obvious slope of 0.5 on the BHPD curve, which can identify the size of the filled-caves. The boundary flow can be used to identify stress-sensitivity. Affected by the stress-sensitivity of the filled-cave, the BHPD’s slope of the boundary flow will be greater than 1. This research work provides technical support for capturing cave and fracture parameters in the fractured reservoir.

Although technical advances in hydraulically fracturing and drilling enable commercial production from tight reservoirs, oil/gas recovery remains at a low level. Due to the technical and economic limitations of well-testing operations in tight reservoirs, rate-transient analysis (RTA) has become a more attractive option. However, current RTA models hardly consider the effect of the non-uniform production on rate decline behaviors. In fact, PLT results demonstrate that production profile is non-uniform. To fill this gap, this paper presents an improved RTA model of multi-fractured horizontal wells (MFHWs) to investigate the effects of non-uniform properties of hydraulic fractures (production of fractures, fracture half-length, number of fractures, fracture conductivity, and vertical permeability) on rate transient behaviors through the diagnostic type curves. Results indicate obvious differences on the rate decline curves among the type curves of uniform properties of fractures (UPF) and non-uniform properties of fractures (NPF). The use of dimensionless production integral derivative curve magnifies the differences so that we can diagnose the phenomenon of non-uniform production. Therefore, it’s significant to incorporate the effects of NPF into the RDA models of MFHWs, and the model proposed in this paper enables us to better evaluate well performance based on long-term production data.

This paper investigates a practical time-varying formation control method for quadrotors subjected to disturbances, uncertainties, and switching-directed topologies. A fully distributed formation control scheme is proposed using a linear-velocity independent position controller (LVIPC) and a nonsingular terminal sliding mode attitude controller (NTSMAC). A distributed observer is adopted to eliminate the measurement of linear-velocity states, and only local neighbor states are needed to realize formation flight. A time-varying nonsingular terminal sliding mode manifold is designed to suppress the reaching phase and ensure the finite-time convergence. Adaptive estimators are employed to remove the reliance on the prior knowledge of the upper bound of lumped uncertainties. It is then proven that all the closed-loop signals are bounded under the proposed method. Comparative experimental results based on a practical outdoor hardware solution are presented to confirm the effectiveness of the suggested control algorithm.

Accurate prediction of production dynamics in chemical composite cold production (CCCP) for heavy oil reservoirs remains challenging due to complex multi-phase fluid interactions and nonlinear flow regime transitions. Traditional numerical simulations are computationally expensive and rely heavily on detailed geological characterization. To address these limitations, a data-driven predictive framework integrating physical mechanisms with machine learning is proposed. A dual-driven feature selection strategy combining Spearman rank correlation and the Entropy Weight Method (EWM) was applied to quantify nonlinear parameter correlations and data informativeness, identifying injection-production balance and development and maximum adsorption capacity as dominant factors controlling oil production fluctuations. Latin Hypercube Sampling (LHS) was used to construct a representative parameter space, followed by weighted standardization. A Multiple Linear Regression (MLR) model was then trained to jointly predict key production indicators. Field validation shows strong predictive capability, with a coefficient of determination above 0.94 and relative fitting error below 5%. The method reduces computational time by over two orders of magnitude while maintaining high precision.

Rubidium and cesium are important strategic resources, and West Taijinar Salt Lake is rich in rubidium and cesium reserves, while the concentration is low and the relationship with coexisting potassium and magnesium ions is complex. In order to understand the evaporative enrichment and salt precipitation patterns of rare elements such as lithium, rubidium, cesium, and boron of the brine after potassium precipitation in West Taijinar Salt Lake, the 288.2 K isothermal evaporation experiment was carried out. The experimental results show that during the evaporation process at 288.2 K, the following salts precipitate from the brine after potassium crystallization: halite (NaCl), bischofite (MgCl2·6H2O), carnallite (KCl·MgCl2·6H2O), hexahydrite (MgSO4·6H2O), epsomite (MgSO4·7H2O), boric acid (H3BO3), and lithium sulfate monohydrate (Li2SO4·H2O). The concentrations of lithium and boron are significantly enriched, the content of Li+ was enriched from 1.7 g/L to 5.63 g/L, and the B2O3 content was enriched from 6.72 g/L to 50.78 g/L. The isomorphism phenomenon of Rb+, Cs+, and K+ makes Rb+ and Cs+ enter potassium ore to form solid solution-type carnallite ((K, Rb)MgCl3·6H2O, (K, Cs)MgCl3·6H2O)) and reduce the content of brine. This study provides data support for the development and comprehensive utilization of lithium, boron, rubidium, and cesium resources in West Taijinar Salt Lake.