Explore the vast range of titles available.

Based on molecular simulation methods, this paper constructs a molecular model of the CH4-drilling fluid system to conduct an in-depth analysis of the microscopic dissolution behavior of CH4 in drilling fluids. By utilizing key parameters such as molecular motion trajectories, interaction energies and solubility free energies, the mechanisms of CH4 dissolution and diffusion are revealed. The factors influencing CH4 solubility and their variation mechanisms are elucidated at the molecular level. Through gas solubility experiments, the variation patterns of CH4 solubility in drilling fluids under different temperature and pressure conditions are investigated, and optimized solubility models for CH4-drilling fluid systems are selected. The results indicate that the dissolution and diffusion behavior of CH4 in drilling fluids can be described using free volume, interaction energy and solubility free energy, with the degree of influence ranked as follows: interaction energy > free volume > solubility free energy. The interaction and free volume of CH4 in oil-based drilling fluids are both greater than those in water-based drilling fluids, suggesting a higher solubility of CH4 in oil-based drilling fluids. Solubility models of CH4 in drilling fluids under conditions of 30~120 °C and 10~60 MPa are obtained by regression. The research findings not only deepen the understanding of the dissolution and diffusion behavior of CH4 in drilling fluids for shale gas horizontal wells, but also provide crucial parameters for establishing wellbore pressure models in managed pressure drilling.

The study of wellbore stability in offshore gas hydrate reservoirs is an important basis for the large-scale exploitation of natural gas hydrate resources. The wellbore stability analysis model in this study considers the evolution of the reservoir mechanical strength, wellbore temperature, and pressure parameters along the depth and uses plastic strain as a new criterion for wellbore instability. The wellbore stability model couples the hydrate phase transition near the wellbore area under the effect of the wellbore temperature and pressure field and the ‘heat–fluid–solid’ multifield evolution characteristics, and then simulates the stability evolution law of the wellbore area during the drilling process in the shallow seabed. The research results show that, owing to the low temperature of the seawater section and shallow formation, the temperature of the drilling fluid in the shallow layer of the wellbore can be maintained below the formation temperature, which effectively inhibits the decomposition of hydrates in the wellbore area. When the wellbore temperature increases or pressure decreases, the hydrate decomposition rate near the wellbore accelerates, and the unstable area of the wellbore will further expand. The research results can provide a reference for the design of drilling parameters for hydrate reservoirs.

The South China Sea has abundant reserves of natural gas hydrates, and if developed effectively, it can greatly alleviate the pressure on the energy supply in China. But the hydrate reservoirs in the sea area are loose, shallow, porous, and have poor mechanical properties. During the drilling process, the invasion of drilling fluid into this kind of reservoir is likely to induce mass decomposition of gas hydrate and, in turn, a significant reduction in mechanical strength around the wellbore as well as instability of the wellbore. In this study, in light of the engineering background of exploratory wells at the South China Sea, a temperature and pressure field model in a gas hydrate reservoir at sea during open circuit drilling was established, and then, based on this model, a comprehensive model for the stability analysis of the well drilled in the hydrate reservoir at sea was constructed, both of them with errors of less than 10%. With these two models, the effects of different drilling parameters on wellbore stability were investigated. The gas and liquid produced by the decomposition of hydrates in the formation will increase the pore pressure in the formation, thereby reducing the effective stress in the formation. The closer the formation is to the wellbore, the more thorough the decomposition of hydrates in the formation and the greater the effective plastic strain. Keeping all other conditions constant, the increase in drilling fluid invasion pressure and temperature, as well as reservoir permeability, will lead to a decrease in the mechanical strength of the formation around the wellbore and an expansion of the wellbore yield zone. The results can provide a theoretical reference for the stability analysis at sea.

Natural gas hydrate is a kind of low-carbon and clean new energy, so research on its efficient extraction in terms of theory and technology is particularly important. Combined thermal injection and depressurization is an effective method for extracting natural gas hydrate. In this study, the classical local heat equilibrium model was modified, and a pore-scale fully coupled unsteady heat transfer model for hydrate reservoirs was set up by considering multiple forms of heat flow accompanying hydrate’s decomposition and gas–liquid flow. Based on this model and the basic geological information of the X2 hydrate reservoir in the western Pacific Ocean, a numerical model of gas hydrate extraction using combined heat injection and depressurization was constructed to simulate the production performance of the hydrate reservoir. The results were fully compared with the results obtained by the depressurization method alone. The results indicated the hydrate extraction via a combined heat injection and depressurization would have a cumulative gas production of 31.609 million m3 and a cumulative water production of 1.5219 million m3, which are 72.57% higher and 31.75% lower than those obtained by depressurization alone, respectively. These study results can provide theoretical support for the industrial extraction of gas hydrate in seas.

Most Rashba spin splitting experimentally studied so far has ideal lattice with inversion symmetry broken, which limits the possibility to minimize the presence of spin-degenerate carriers near the Fermi level. Here, we report a novel 2D Au 2 Sb surface alloy decorated with periodic structural defects that exhibits modulation on the Rashba spin-orbit coupling band. Spin- and angle-resolved photoemission spectroscopy reveals a Rashba spin-split band with antiparallel spin polarization, significantly broadened compared to the Au₂Sn surface alloy. From the good agreement between the experimental results and DFT calculations, we identify that the broadening of the Rashba bands comes from variations in Sb atom corrugation induced by the periodic three-pointed star-shaped defects. These periodic defects can shift the energy position of the Rashba bands without breaking the in-plane rotational and mirror symmetries. Our findings highlight the potential to tune spin-dependent properties in 2D materials for spintronic applications.

To address the challenges of high running friction and limited depth extension caused by the heavy weight of traditional carbon steel casings in extended-reach horizontal wells, this study conducts a comparative analysis of titanium alloy and carbon steel casings using WellLead drilling software in a deep-water shallow-soft formation well (with a water-to-vertical ratio of 2.36 and maximum dogleg severity of 15°/30m). The friction sensitivity curve model reveals that the titanium alloy casing reduces static hook load by 13.2% (73 kN), significantly mitigating pipe sagging risks. Notably, under a high external friction co-efficient of 0.6, the titanium alloy casing achieves a hook load margin of 142.6 kN—107% higher than that of carbon steel casing (68.7 kN), thereby fully avoiding critical running failures. Simulation of a 5,000-meter lateral section demonstrates that the titanium alloy casing extends the maximum running depth by 2.4% (high friction: 0.6) to 27.4% (low friction: 0.6) compared to carbon steel. Field tests confirm superior running stability of titanium alloy casings in irregular wellbores, though wellbore reconditioning remains necessary for localized obstructions. This study quantifies the relationship between lightweight design and friction sensitivity, providing a reliable basis for casing selection in complex horizontal wells. Future research should also examine potential risks of titanium alloy casings, particularly weldability and long-term durability.

Titanium alloy tubing is an ideal material for extreme oil and gas environments—characterized by high temperature, high pressure, and H2S/CO2/chloride-rich conditions—due to its low density, high strength, excellent corrosion resistance, and fatigue performance. Internationally, Grade 28/29 titanium alloys developed by RMI have been successfully applied in sour gas wells, while Weatherford’s Ti-6Al-4V drill pipes exhibit fatigue resistance ten times higher than steel counterparts. Domestic research started later, yet Chinamade titanium alloy casings achieved their first successful application in natural gas hydrate trial production in 2020, with collapse resistance exceeding 42 MPa. Key failure modes include pitting, crevice, and galvanic corrosion, especially when passive films are damaged under high-temperature (>70 °C) or reducing acidic conditions. While corrosion inhibitors (e.g., Na2MoO4) reduce corrosion rates, novel inhibitors for temperatures above 160 °C are still needed. For wear resistance, surface modifications such as TiN or DLC coatings and multilayer coating technologies significantly improve performance. Non-marking running and pulling techniques with optimized jaw designs can limit tooth marks to <0.08 mm, demonstrating effectiveness in high-sulfur environments. Future developments should focus on high-temperature acid-resistant inhibitors, hard-soft alternate coatings, and damage-free running technologies to enable large-scale applications in deep-well and offshore oil and gas operations.

Based on molecular simulation methods, this paper constructs a molecular model of the CH[sub.4]-drilling fluid system to conduct an in-depth analysis of the microscopic dissolution behavior of CH[sub.4] in drilling fluids. By utilizing key parameters such as molecular motion trajectories, interaction energies and solubility free energies, the mechanisms of CH[sub.4] dissolution and diffusion are revealed. The factors influencing CH[sub.4] solubility and their variation mechanisms are elucidated at the molecular level. Through gas solubility experiments, the variation patterns of CH[sub.4] solubility in drilling fluids under different temperature and pressure conditions are investigated, and optimized solubility models for CH[sub.4]-drilling fluid systems are selected. The results indicate that the dissolution and diffusion behavior of CH[sub.4] in drilling fluids can be described using free volume, interaction energy and solubility free energy, with the degree of influence ranked as follows: interaction energy > free volume > solubility free energy. The interaction and free volume of CH[sub.4] in oil-based drilling fluids are both greater than those in water-based drilling fluids, suggesting a higher solubility of CH[sub.4] in oil-based drilling fluids. Solubility models of CH[sub.4] in drilling fluids under conditions of 30~120 °C and 10~60 MPa are obtained by regression. The research findings not only deepen the understanding of the dissolution and diffusion behavior of CH[sub.4] in drilling fluids for shale gas horizontal wells, but also provide crucial parameters for establishing wellbore pressure models in managed pressure drilling.

Recent experiments in ultracold atoms have reported the realization of quantum anomalous Hall phases in spin-orbit coupled systems. Motivated by such advances, we investigate spin-orbit coupled Bose-Bose mixtures in a two-dimensional square optical Raman lattice. Complete phase diagrams are obtained via a nonperturbative real-space bosonic dynamical mean-field theory. Various quantum phases are predicted, including Mott phases with z -ferromagnetic, xy -antiferromagnetic and vortex textures, and superfluid phases with the exotic spin orders, induced by the competition between the lattice hopping and spin-orbit coupling. To explain the underlying physics in the Mott regime, an effective Hamiltonian is derived based on second-order perturbation theory, where pseudospin order stems from the interplay of effective Dzyaloshinskii-Moriya superexchange and Heisenberg interactions. In the presence of the Zeeman field, the competition of strong interaction and Zeeman energy facilitates a topological phase, which is confirmed both by the nontrivial topological Bott index and spectral function with topological edge states. Our work indicates that spin-orbit coupling can induce rich non-Abelian topological physics in strongly correlated ultracold atomic systems.

In this thesis, the interplay of spin waves and domain walls in magnetic nanostructures is studied in three aspects: (1) how a domain wall can propagate in a magnetic field through emitting spin waves, (2) how an externally generated spin wave can drive a domain wall’s propagation, whose mechanism is called “all-magnonic spin transfer torque”, and (3) how spin wave excitations affect the thermodynamic properties of a domain wall system and drive the domain wall propagation in a temperature gradient. We theoretically study field-induced domain wall motion in an electrically insulating ferromagnet with hard- and easy-axis anisotropies. Domain walls can propagate along a dissipationless wire through spin wave emission locked into the known soliton velocity at low fields. In the presence of damping, the usual Walker rigid-body propagation mode can become unstable for a magnetic field smaller than the Walker breakdown field. We also numerically investigate the properties of spin waves emitted by the domain wall motion, such as frequency and wave number, and their relation with the domain wall motion. For a wire with a low transverse anisotropy and in a field above a critical value, a domain wall emits spin waves to both sides (bow and stern), while it oscillates and propagates at a low average speed. For a wire with a high transverse anisotropy and in a weak field, the domain wall emits mostly stern waves, while the domain wall distorts itself and the domain wall center propagates forward like a drill at a relative high speed. The spin wave transportation through a transverse magnetic domain wall in a magnetic nanowire is studied. It is found that in a 1D nanowire, the spin wave passes through a domain wall without reflection. A magnon, the quantum of the spin wave, carries opposite spins on the two sides of the domain wall. As a result, there is a spin angular momentum transfer from the propagating magnons to the domain wall. This magnonic spin transfer torque can efficiently drive a domain wall to propagate in the opposite direction to that of the spin wave. Micromagnetic simulations show that generally, in nanostrips, spin waves (or magnons) interact with magnetic domain walls in a more complicated way that a domain wall can propagate either along or against magnon flow. However, thermally activated magnons always drive a domain to the hotter region of a nanowire of magnetic insulators under a temperature gradient. We theoretically illustrate why this is surely so by showing that domain wall entropy is always larger than that of a domain as long as the material parameters do not depend on spin textures. Equivalently, the total free energy of the wire can be lowered when the domain wall moves to the hotter region. The larger domain wall entropy is related to the increase of magnon density of states at low energy originating from the gapless magnon bound states.