超临界CO2气爆非均质煤体破裂规律模拟研究

为揭示超临界CO2气爆含割理裂隙非均质煤体的致裂规律,开发了识别实际煤体图像获取其割理裂隙几何信息的M atlab程序,将几何信息与煤体非均质物性参数关联并导入Abaqus中,实现了非均质煤体有限元表征,并采用SPH与FEM联合求解的方法模拟超临界CO2气爆非均质煤体的致裂过程,得到了弱面倾角、弱面到爆孔中心距离及初应力的变化对煤体气爆致裂效果的影响规律.模拟结果表明,初应力对主裂缝的萌生和扩展具有导向作用,气爆裂缝沿最大初应力方向扩展;弱面倾角相同时,弱面离爆孔越近,穿过弱面的裂缝尺度和密度越大,弱面离爆孔较远时,弱面完全阻断了裂缝的扩展;弱面到爆孔中心距离相同时,弱面倾角越大,弱面对裂缝扩展的阻碍作用越大,穿过弱面的裂缝尺度和密度越小,应力波透射率越小.现场气爆增透煤体时,应考虑割理裂隙和地应力特征合理布置气爆孔位置及爆破参数.     

不同温压超临界CO2气爆喷孔冲击应力变化规律实验研究

为研究不同温压条件下超临界CO2气爆过程中气爆管喷孔喷射的爆生气体对被爆物体产生的冲击应力变化规律,自主设计了超临界CO2气爆实验系统及数据采集装置,实验得到了在不同初始温度和压力下对称双喷孔喷射的超临界CO2气爆爆生气体冲击应力变化规律:喷孔喷出的爆生气体作用于被爆物体的冲击应力经历应力激增、应力剧减和应力减速衰减三个阶段。冲击应力时程变化曲线呈脉冲波形曲线特征,且冲击应力衰减阶段持续时间大于冲击应力激增持续时间。冲击应力随初始温度和初始压力的增大而增加,初始压力变化引起的气爆冲击应力变化比初始温度变化明显,增大超临界态CO2的初始压力提高气爆冲击应力优于提高超临界态CO2的初始温度。最后得到了冲击应力峰值Pmax与初始温度T和初始压力P的关系Pmax=ɑT+bP+C。     

页岩油藏注CO2增能开发数值模拟研究

页岩油开发对胜利油田产能接替具有重要意义。页岩油藏渗透率低,难以注水补充能量,CO₂易注入地层且能够改善原油流动条件,是页岩油增能开发的有效方法。但是页岩油藏包含微纳米级孔隙-微米级微裂缝-米级大裂缝多个尺度孔隙空间,且开发过程涉及组分相态变化,是一个多尺度多相多组分渗流的复杂过程。本文构建嵌入式离散裂缝模型表征裂缝系统,建立不同尺度孔隙间传导率将基岩系统与裂缝系统联系在一起,实现页岩油藏注CO₂开发高效模拟。采用本模型研究了开发参数及裂缝参数等对开发效果的影响,结果表明,CO₂吞吐能够有效补充地层能量,提高页岩油开发效果。页岩油注CO₂吞吐时机不宜过早或者过晚,应充分利用地层能量,同时考虑及时注气补充能量。而且人工裂缝对开发效果影响明显,需要结合经济因素优化压裂参数。     

包覆型纳米CeO2@SiO2复合磨料的制备?表征及其抛光性能

以无水乙醇为溶剂,氨水为催化剂,利用正硅酸乙酯(TEOS)水解,并在500℃下煅烧1h,制备了SiO2粉体.将SiO2粉体作为内核浸渍到以硝酸亚铈、乙酰丙酮和正丙醇为原料制备的铈溶胶中,得到包覆型CeO2@SiO2复合粉体.利用XRD、SEM、TEM和FT-IR等测试手段,对所制备样品的物相结构、形貌、粒径大小、团聚情况进行表征.将所制备的包覆型CeO2@SiO2复合粉体配制成抛光浆料用于砷化镓晶片的化学机械抛光,用原子力显微镜(AFM)观察抛光表面的微观形貌,测量表面粗糙度.结果表明,采用浸渍工艺成功制备出单分散球形,粒径在400～450nm,负载均匀的包覆型CeO2@SiO2复合粉体.复合粉体中CeO2的包覆量随着铈溶胶中铈离子浓度的升高而增大.经包覆型CeO2@SiO2复合磨料抛光后的砷化镓晶片表面的微观起伏更趋于平缓,在1μm×1μm范围内表面粗糙度Ra值为0.819nm,获得了具有亚纳米量级粗糙度的抛光表面.     

CO2微气泡溶解动力学及提高采收率机理研究

CO₂微气泡是一种具有潜力的提高采收率与碳埋存方法,本文在自主设计的CO₂微气泡发泡装置的基础上,表征了高温高压条件下微气泡形态,进一步研究了微气泡的溶解特征,研究结果表明:10 MPa下制备出的微气泡直径10～70μm,平均直径34.43μm; 15 MPa下制备的微气泡直径更小,平均直径25.03μm;地层水高矿化度条件下,平均气泡直径277.17μm,且气泡稳定性降低.微气泡的溶解实验结果表明CO₂微气泡的溶解速率较高,但是未溶解的CO₂仍以气泡的形式在地层中运移,微气泡注入地层后将形成“碳化水+微气泡”的运移模式.采用可视化微流控平台,首次研究了高温高压条件下无化学剂辅助CO₂微气泡的提高采收率机理:(1)提高微观洗油效率;(2)通过体积膨胀、溶解携带作用将油滴带出盲端,采出盲端中的剩余油;(3)打破油滴的毛管压力平衡状态,采出柱状残余油;(4)在流动中产生“贾敏效应”,封堵大孔隙、提高波及效率.本文研究可为CO₂微气泡提高油藏采收率与碳封存提供指...     

页岩储层纳微米孔隙CO2/CH4吸附及驱替特性研究进展

利用CO₂开采页岩气不仅能够提高页岩气采收率, 还能够节省水资源并且对CO₂进行地质封存, 有助于实现页岩气开采过程的碳中和. 富有机质页岩储层纳微米孔隙中气体运移机制不同于常规储层, CO₂在储层中具有超临界特性, 致使开采机理复杂, 无法得到CO₂开采页岩气微观机理的准确认识, 所以研究CH₄, CO₂及其二元混合物在页岩储层纳微米孔隙中的吸附及驱替特性对准确评估和高效开采页岩气至关重要. 本文从实验、理论以及模拟方面对页岩储层纳微米孔隙中CH₄的吸附特性、CO₂/CH₄二元混合物竞争吸附特性以及驱替特性进行了综合分析, 对气体在纳微米孔隙中吸附及驱替特性的基础研究及关键问题进行讨论分析并提出了展望. 研究表明CH₄在页岩储层中表现为物理吸附, 有机质特征(丰度、成熟度、类型)、孔隙结构、无机矿物组成、温度和压力、含水率对页岩的CH₄吸附能力均有一定程度的影响. 在相同条件下, CO₂比CH₄更易被页岩储层吸附, 在页岩储层中注入CO₂可以促进CH₄的解吸, 并有利于CO₂的地质埋存. 开采方案的部署可采用井网形式的注采方式, 可以通过调整注入井的位置、数量以及CO₂注入速率对开采方案进行优化.      

CO2地质封存力学问题的数值模拟方法综述

二氧化碳捕集、利用和封存是现阶段被广泛认可的减少二氧化碳排放最有效的途径之一, 是助力我国实现2060年碳中和目标的重要措施. 在二氧化碳地质封存过程中, 储层−盖层系统多场耦合数值模拟是认识二氧化碳长期封存过程和论证封存安全性的核心技术. 文章对二氧化碳地质封存储层−盖层系统风险分析的流固热化多场耦合数值模拟技术进行了全面综述, 首先给出二氧化碳地质封存多场耦合问题的数学模型, 其基本控制方程包括应力平衡方程、质量和能量守恒方程、化学反应和本构关系等; 其次总结了全耦合、迭代耦合、弱耦合、显式耦合和拟耦合等常用的耦合问题数值解法; 然后介绍了CO₂泄漏、地表变形、断层活化和裂缝拓展等地质风险的分析方法; 最后针对当前我国二氧化碳地质封存数值模拟技术面临的主要问题, 对未来的研究方向给出了建议. 论文能够为CO₂地质封存场地尺度的相关研究提供有价值的参考.     

煤炭地下气化腔CO2埋存的研究进展及发展趋势

CO₂捕集与埋存(CCS)可助力碳达峰、碳中和战略目标实现,是解决温室效应的重要手段.在众多地质埋存空间中,煤炭地下气化(UCG)后的气化腔近年来成为埋存研究的热点,但与传统埋存方式相比,相关工作仍处于理论探索阶段,缺乏现场实施案例.为推动该埋存方式的发展,文章从以下3方面开展工作.(1)介绍UCG和CO₂气化腔埋存的国内外研究进展,并将后者的发展划分为概念提出阶段、潜力评价和可行性分析阶段以及机理分析阶段,目前尚处于理论探索阶段.(2)从注入性、密闭性、经济性、储容量和CO₂埋存机理等多个角度出发,通过与其他埋存方式对比,分析了气化腔埋存的特点与优势:注入性良好;密闭性与未开发煤层类似,但更为复杂;显著节约CO₂运输成本;埋存潜力巨大;埋存机理非常复杂,需要考虑气化腔形态、边壁性质以及超临界CO₂与气化腔流体间复杂相互作用对注入和长期埋存过程的影响.(3)阐明CO₂气化腔埋存所涉及的关键科学问题和工程问题,并指出未来发展趋势.在以上工作的基础上,建议国家...     

惰性气体对C3H8可燃下极限的影响

为探究CO₂、N₂和Ar对C₃H₈可燃下极限的影响,在5 L爆炸容器中测定了C₃H₈在O₂/CO₂、O₂/Ar、O₂/N₂三种气氛下的可燃下极限。首先分析了稀释气浓度、稀释气种类和氧气浓度对C₃H₈的可燃下极限的影响。结果表明,在O₂/CO₂气氛下,稀释气浓度变化对C₃H₈的可燃下极限影响最大,对O₂/Ar的影响次之,对O₂/N₂的影响最小。在相同稀释气浓度条件下,CO₂对C₃H₈可燃下极限的影响最大,N₂的影响次之,Ar的影响最小。随着O₂浓度的上升,O₂/CO₂气氛的可燃下极限出现较为明显的下降,O₂/N₂和O₂/Ar的氛围的可燃下极限平缓上升。通过建立能量平衡方程分析了稀释气的比热和辐射效应对可燃下极限的影响。结果表明,混合气比热的改变是C₃H₈可燃下极限改变的主要原因,辐射热损失是影响可燃下极限的重要因素。     

超临界CO2作用时间对煤渗透率和孔隙率的 影响规律研究

为研究超临界CO2作用后煤渗透率和孔隙率的变化规律,在超临界CO2增透实验基础上进行了微观成像实验,提取煤微观孔隙特征,计算孔隙率,得到了煤孔隙率和渗透率变化的等值线图.结果表明:经超临界CO2作用后,煤的渗透率较作用前提高了一个数量级,并随超临界CO2作用时间的延长呈正指数增加,当作用时间为20h时,煤的渗透率较增透前提高了20.2倍;随超临界CO2作用时间的增加,蜂窝状孔隙逐渐向更为细小的颗粒空间发展,孔隙数量明显增加.增透煤微观孔隙定量结果显示,随着超临界CO2作用时间的增加,孔隙率等值线密集程度增加,煤各微区孔隙逐渐发育,孔隙率增加,当作用时间增加到20h时,孔隙率较增透前提高了17.20倍.煤的渗透率随孔隙率的增加呈正指数递增,说明宏微观结果是一致的,超临界CO2增透促进了煤微观结构的有效发育,提高了煤的渗透率.     

Computational fluid dynamics analysis of diffuser performance in gas-powered jet pumps

Jet pump diffuser performance is analyzed, both in terms of past experimental work dealing with the high inlet flow distortions involved and in the sense that this problem is amenable to predictive investigation by computational fluid dynamics techniques. In these highly nonuniform flow conditions, diffusers are seen to justify their inclusion in a jet pump design, for regaining static pressure downstream of the vacuum chamber, even though their performance in effectiveness terms is lowered by about two thirds at high inlet glow distortion levels. A satisfactory correlation has been found between outlet and inlet conditions and diffuser area ratio, extending well beyond past experimental published results for diffuser geometry and distorted inlet flows.     

A compressible two‐fluid multiphase model for CO2 leakage through a wellbore

This paper introduces an effectively mesh‐independent and computationally efficient model for CO₂ leakage through wellbores. A one‐dimensional compressible two‐fluid domain, representing a homogeneous air gas and a multiphase CO₂ with a jump at the interface between them, is modeled. The physical domain is modeled using the drift‐flux model, and the governing equations are solved using a mixed finite‐element discretization scheme. The standard Galerkin FEM, the partition of unity method, and the level‐set method are integrated to solve the problem. All important physical phenomena and processes occurring along the wellbore path, including fluid dynamics, buoyancy, phase change, compressibility, thermal interaction, wall friction, and slip between phases, together with the jump in density and enthalpy between air and CO₂, are considered. Two numerical examples illustrating the computational capability and efficiency of the model are presented. Copyright © 2015 John Wiley & Sons, Ltd.     

Sensitivity analysis of low Reynolds number channel flow using the finite volume method

An unsteady finite volume‐based fractional step algorithm solved on a staggered grid has been developed for computing design sensitivity parameters in two‐dimensional flows. Verification of the numerical code is performed for the case of low Reynolds number, pressure‐driven flow through a straight channel, which has an exact steady‐state solution to the Navier–Stokes equations. Sensitivity of the flow to the channel height, fluid viscosity, and imposed pressure gradient is considered. Three different numerical techniques for computing the design sensitivity parameters: finite difference, complex‐step differentiation, and sensitivity equation method (SEM), are compared in terms of numerical error (relative to the exact solution), computational expense, and ease of implementation. Results indicate that, of all the three methods, complex step is the most accurate and requires the least computational time. In addition, treatment of the boundary conditions in SEM is addressed, within the framework of the present finite volume approach, with special attention given to parameter dependence in the boundary conditions. Error estimation based on the Grid Convergence Index provides a good indication of the exact error in the SEM solutions. An example of application of the use of sensitivity parameters to estimate the propagation of input uncertainty through the numerical simulation is also provided. Copyright © 2007 John Wiley & Sons, Ltd.     

One‐dimensional simulation of supercritical flow at a confluence by means of a nonlinear junction model applied with the RKDG2 method

We investigate the one‐dimensional computation of supercritical open‐channel flows at a combining junction. In such situations, the network system is composed of channel segments arranged in a branching configuration, with individual channel segments connected at a junction. Therefore, two important issues have to be addressed: (a) the numerical solution in branches, and (b) the internal boundary conditions treatment at the junction. Going from the advantageous literature supports of RKDG methods to a particular investigation for a supercritical benchmark, the second‐order Runge–Kutta discontinuous Galerkin (RKDG2) scheme is selected to compute the water flow in branches. For the internal boundary handling, we propose a new approach by incorporating the nonlinear model derived from the conservation of the momentum through the junction. The nonlinear junction model was evaluated against available experiments and then applied to compute the junction internal boundary treatment for steady and unsteady flow applications. Finally, a combining flow problem is defined and simulated by the proposed framework and results are illustrated for many choices of junction angles. Copyright © 2007 John Wiley & Sons, Ltd.     

小尺寸管道内二氧化碳抑制甲烷爆炸效果的实验及数值模拟

为了有效防治矿井瓦斯爆炸事故, 以瓦斯的主要成分甲烷作为模拟气体, 运用自主设计改装的XKWB-S型小尺寸石英玻璃管道实验系统, 结合高速摄影仪, 并采用FLACS数值模拟软件, 研究惰性气体抑爆条件下甲烷燃烧爆炸特性, 进行体积分数为6%~27%的CO₂抑制体积分数为9%CH₄爆炸的实验及数值模拟, 结果表明:各组分混合气体在爆炸传播过程中, 爆炸压力、火焰锋面速度和气体运动速度均呈现一定程度的波动, 且压力和速度没有同时达到最大值; CO₂的加入有效抑制了甲烷/空气反应, 且添加CO₂体积分数越大, 抑爆效果越明显, 模拟结果与实验结果基本吻合。     

非常规结构武器两相流内弹道的高精度数值模拟

针对侧装药武器的结构特点,在提出等效物理模型的基础上建立了双一维两相流模型,并对主膛的气、固相方程组分别采用二阶精度TVD算法进行了模拟,结果与12.7 mm口径的发射实验进行了对比分析,模型和算法是可行的。     

A study on the behaviour of high-order flux reconstruction method with different low-dissipation numerical fluxes for large eddy simulation

This work focuses on the numerical dissipation features of high-order flux reconstruction (FR) method combined with different numerical fluxes in turbulence flows. The famous Roe and AUSM+ numerical fluxes together with their corresponding low-dissipation enhanced versions (LMRoe, SLAU2) and higher resolution variants (HR-LMRoe, HR-SLAU2) are incorporated into FR framework, and the dissipation interplay of these combinations is investigated in implicit large eddy simulation. The numerical dissipation stemming from these convective numerical fluxes is quantified by simulating the inviscid Gresho vortex, the transitional Taylor–Green vortex and the homogenous decaying isotropic turbulence. The results suggest that low-dissipation enhanced versions are preferential both in high-order and low-order cases to their original forms, while the use of HR-SLAU2 has marginal improvements and the HR-LMRoe leads to degenerated solution with high-order. In high-order the effects of numerical fluxes are reduced, and their viscosity may not be dissipative enough to provide physically consistent turbulence when under-resolved.