页岩气及其吸附与扩散的研究进展

随着当前能源消费的迅速增加,常规天然气资源短缺,很难满足日益增长的能源需求。页岩气作为一种非常规天然气,具有资源潜力大和低碳排放等优点,加之美国和加拿大成功实现商业化开采,因此页岩气资源勘探开发近年来备受世界瞩目。中国作为重要的页岩气开采国家,近几年发展势头良好,部分页岩气田也已经实现商业化生产。由于页岩的致密和低渗特性,导致页岩气的开采难度较大。页岩的孔隙结构和气体吸附扩散研究,对于气藏产能的评估及其高效开采有至关重要的作用。本文介绍了国内外页岩气勘探开发现状以及页岩的孔隙结构,综述了储层中页岩气吸附、扩散与渗流的研究进展,总结了分子模拟方法在页岩气研究中的应用,并对页岩气相关研究的前景进行了展望。     

A model for gas transport in microfractures of shale and tight gas reservoirs

A model for gas transport in microfractures of shale and tight gas reservoirs is established. Slip flow and Knudsen diffusion are coupled together to describe general gas transport mechanisms, which include continuous flow, slip flow, transitional flow, and Knudsen diffusion. The ratios of the intermolecular collision frequency and the molecule‐wall collision frequency to the total collision frequency are defined as the weight coefficients of slip flow and Knudsen diffusion, respectively. The model is validated by molecular simulation results. The results show that: (1) the model can reasonably describe the process of the mass transform of different gas transport mechanisms; (2) fracture geometry significantly impacts gas transport. Under the same fracture aperture, the higher the aspect ratio is, the stronger the gas transport capacity, and this phenomenon is more pronounced in the cases with higher gas pressure and larger fracture aperture. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2079–2088, 2015     

Modified gas‐translation model for prediction of gas permeation through microporous organosilica membranes

A modified gas‐translation (GT) model was applied for the theoretical analysis of gas permeation through microporous organosilica membranes derived from bis(triethoxysilyl)ethane (BTESE) via a sol–gel method using different water/alkoxide molar ratios. The pore sizes of BTESE‐derived membranes were quantitatively determined by normalized Knudsen‐based permeance analysis, which was based on a modified‐GT model, using experimentally obtained permeances of He, H₂, N₂, C₃H₈, and SF₆. The pore sizes of BTESE‐derived membranes were successfully controlled from 0.65 to 0.46 nm by increasing the H₂O/BTESE ratio from 6 to 240. Furthermore, theoretical correlations of all possible pairs of permeance ratios were calculated based on the modified‐GT model. The experimental data were in good agreement with the theoretical correlation curves, indicating that the modified‐GT model can clearly explain gas permeation mechanisms through microporous membranes, and, thus, can be used to predict the gas permeation properties for these membranes. © 2014 American Institute of Chemical Engineers AIChE J 60: 4199–4210, 2014     

Preparation and gas permeation of immobilized fullerene membranes

Fullerene‐dispersed membranes were homogeneously prepared under the conditions in which a 10 wt % polystyrene solution containing 1 wt % fullerene was dried under a reduced pressure of 50 cmHg at room temperature. The fullerene membranes prepared with 1,2‐dichlorobenzene were found to have the darkest color, and showed no evidence of fullerene crystals in their photomicrographs. UV‐visible and infrared absorption spectra of the fullerene membranes showed fullerene bands, which indicated that the fullerene was homogeneously dispersed in the membranes. The permeability coefficients of pure nitrogen, oxygen, carbon dioxide, ethane, and ethylene were found to increase significantly in the fullerene membranes compared to those in the polystyrene membranes, although the ideal separation factors for oxygen/nitrogen and ethylene/ethane in the fullerene membranes (i.e., 4.3 and 1.7, respectively) were slightly less than the separation factors in the polystyrene membranes. The permeability increase originated from the increase in diffusion coefficients in the fullerene membranes. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 529–537, 2000     

Displacement of shale gas confined in illite shale by flue gas: A molecular simulation study

The shale gas is an unconventional supplementary energy to traditional fossil energy, and is stored in layered rocks with low permeability and porosity, which leads to the difficulty for exploration of shale gas. Therefore, using CO₂ gas to displace shale gas has become an important topic. In this work, we use molecular simulations to study the displacement of shale gas by flue gas rather than CO₂, in which flue gas is modeled as a binary mixture of CO₂ and N₂ and the shale model is represented by inorganic Illite and organic methylnaphthalene. CH₄ is used as a shale gas model. Compared to the pure CO₂, flue gas is easily available and the cost of displacement by flue gas would become lower. Results indicate that the pore size of shale is an important factor in the process of displacing shale gas and simultaneously sequestrating flue gas, while the flue gas N₂-CO₂ ratio shows a small effect on the process of CH₄ displacement, because the high partial pressure of flue gas is the main driving force for displacement of shale gas. Moreover, the geological condition also has a significant effect on the process of CH₄ displacement by flue gas. Therefore, we suggest that the burial depth of 1 km is suitable operation condition for shale gas displacement. It is expected that this work provides a useful guidance for exploitation of shale gas and sequestration of greenhouse gas.     

A fractal model for real gas transport in porous shale

A model for real gas flow in shale gas matrices is proposed and consists of two main steps: (a) developing a microscopic (single pore) model for a real gas flow by generalizing our previously reported Extended Navier‐Stokes Equations (ENSE) method and (b) by using fractal theory concepts, up‐scaling the single pore model to the macroscopic scale. A prominent feature of the up‐scaled model is a predictor for the apparent permeability (AP). Both models are successfully validated with experimental data. The impact of the deviation of the gas behavior from ideality (real gas effect) on the gas transport mechanisms is investigated. The effect of the structural parameters (porosity Ф, the maximum pore diameter D_max, and the minimum pore diameter D_min) of the shale matrix on the apparent permeability is studied and a sensitivity analysis is performed to evaluate the significance of the parameters for gas transport. We find that (1) the real gas transport models for a single pore and porous shale matrix are both reliable and reasonable; (2) the real gas effect affects the thermodynamic parameters of the free gas and the adsorption and transport capacity of the adsorbed gas; (3) the real gas effect decreases the effective permeability for convective flow and surface diffusion; i.e., the derivation degree of the effective permeability for bulk diffusion and Knudsen diffusion increases with increasing pressure but presents a bathtub shape when the pore diameter is smaller than 10 nm; and (4) the apparent permeability increases with Ф, D_max, and D_min. It is more sensitive to D_max, followed by the porosity. D_min has a minor impact. © 2016 American Institute of Chemical Engineers AIChE J, 63: 1430–1440, 2017     

A semianalytical model for simulating real gas transport in nanopores and complex fractures of shale gas reservoirs

An efficient gridless semianalytical model was developed to simulate real gas transport in shale formation with nanopores and complex fracture geometry. This model incorporates multiple physics such as gas desorption, adsorbed gas porosity, gas slippage and diffusion, residual water saturation, non‐Darcy flow, choke skin, and pressure‐dependent matrix permeability, and fracture conductivity. Additionally, this model is easy to handle complex fracture geometry through dividing fractures into a number of segments and nodes. We verified the model against a numerical model and an analytical model for bi‐wing hydraulic fractures. After validation, the impacts of all these physics on well performance were evaluated in detail through a series of case studies. The simulation results confirm that modeling of gas production from complex fracture geometry as well as modeling important physics in shale gas reservoirs is significant. This study improves our understanding of critical physics affecting gas recovery in shale gas reservoirs. © 2017 American Institute of Chemical Engineers AIChE J, 63: 326–337, 2018     

Micropore size estimation on gas separation membranes: A study in experimental and molecular dynamics

The effect of the gas molecular size and its affinity to the pore surface on gas permeation properties through the ceramic membranes was studied by both the gas permeation experiments and gas permeation simulations using a nonequilibrium molecular dynamics (MD) technique. A modified gas permeation model equation based on the gas translation (GT) mechanism was presented. MD simulation revealed that the effective diffusion length in a micropore depended on the gas molecular size, and the pre‐exponential coefficient of a modified GT model equation showed good correlation with the kinetic diameter of the gas molecules. Also presented is a simple method to estimate the mean pore size of microporous membranes. The estimated pore sizes were consistent with observed kinetic diameter dependencies of gas permeance for real silica membranes. The pore size of a Deca‐Dodecasil 3R (DDR) zeolite membrane was also reasonably estimated at ～0.4 nm from the reported gas permeation data. © 2012 American Institute of Chemical Engineers AIChE J, 59: 2179–2194, 2013     

An analytical model for real gas flow in shale nanopores with non‐circular cross‐section

An analytical model for gas transport in shale media is proposed on the basis of the linear superposition of convective flow and Knudsen diffusion, which is free of tangential momentum accommodation coefficient. The present model takes into the effect of pore shape and real gas, and is successfully validated against experimental data and Lattice–Boltzmann simulation results. Gas flow in noncircular nanopores can be accounted by a dimensionless geometry correction factor. In continuum‐flow regime, pore shape has a relatively minor impact on gas transport capacity; the effect of pore shape on gas transport capacity enhances significantly with increasing rarefaction. Additionally, gas transport capacity is strongly dependent of average pore size and streamline tortuosity. We also show that the present model without using weighted factor can describe the variable contribution of convective flow and Knudsen diffusion to the total flow. As pressure and pore radius decrease, the number of molecule‐wall collisions gradually predominates over the number of intermolecule collisions, and thus Knudsen diffusion contributes more to the total flow. The parameters in the present model can be determined from independent laboratory experiments. We have the confidence that the present model can provide some theoretical support in numerical simulation of shale gas production. © 2016 American Institute of Chemical Engineers AIChE J, 62: 2893–2901, 2016     

Investment optimization model for freshwater acquisition and wastewater handling in shale gas production

Major challenges of water use in the drilling and fracturing process in shale gas production are large volumes required in a short‐period of time and the nonsteady nature of wastewater treatment. A new mixed‐integer linear programming (MILP) model for optimizing capital investment decisions for water use for shale gas production through a discrete‐time representation of the State‐Task Network is presented. The objective is to minimize the capital cost of impoundment, piping, and treatment facility, and operating cost including freshwater, pumping, and treatment. The goal is to determine the location and capacity of impoundment, the type of piping, treatment facility locations and removal capability, freshwater sources, as well as the frac schedule. In addition, the impact of several factors such as limiting truck hauling and increasing flowback volume on the solution is examined. A case study is optimized to illustrate the application of the proposed formulation. © 2015 American Institute of Chemical Engineers AIChE J, 61: 1770–1782, 2015     

Temperature effects on permeation of modified atmosphere gas mixtures through a low density polyethylene package film

Permeation of CO₂ and O₂ through a low density polyethylene film was studied with CO₂-N₂ mixtures in the temperature range 263-283 K, and with CO₂-O₂-N₂ mixtures in the range 257-313 K. The temperature dependence of the permeabilities of these gases agreed with the Arrhenius expression. The activation energy for carbon dioxide diffusion was between 3.53 × 10⁴ and 3.74 × 10⁴J/mol; the activation energy for oxygen diffusion was 3.13 × 10⁴J/mol. The pre-exponential constant for oxygen was higher than that of carbon dioxide in various mixtures. It was also found that the pre-exponential constant of carbon dioxide decreased with increasing CO₂ concentration in the mixtures.     

油页岩热解的FG-DVC模型

为研究油页岩结构与热解反应性之间的关系,在TG-FTIR分析仪上对甘肃油页岩在不同升温速率条件下（5、20、50℃·min^-1）进行了热解实验研究,对CH₄、CO、CO₂、H₂O和页岩油进行了定量分析,并采用非线性最小二乘拟合方法求解各组分析出的动力学参数,同时采用基于燃料化学结构的FG-DVC模型对各组分的析出过程进行了模拟。结果表明：油页岩的脱挥发分过程主要发生在200～600℃之间;油页岩中有机质所含官能团以脂肪烃为主;由于各官能团活性不同,导致气态产物的析出有先后顺序;由非线性最小二乘拟合方法获得的各种产物析出的活化能E分布在188～239 kJ·mol^-1之间,而指前因子A在10⁹～10¹³ s^-1之间;各产物的FG-DVC模拟结果与实验数据较为相符,这说明用FG-DVC模型来描述甘肃油页岩的热解脱挥发分过程是比较合适的。     

Effect of adjusted mesoscale drag model on flue gas desulfurization in powder-particle spouted beds

An energy minimum multiscale model was adjusted to simulate the mesoscale structure of the flue gas desulfurization process in a powder-particle spouted bed and verified experimentally. The obtained results revealed that the spout morphology simulated by the adjusted mesoscale drag model was unstable and discontinuous bubbling spout unlike the stable continuous spout obtained using the Gidaspow model. In addition, more thorough gas radial mixing was achieved using the adjusted mesoscale drag model. The mass fraction of water in the gas mixture at the outlet determined by the heterogeneous drag model was 1.5 times higher than that obtained by the homogeneous drag model during the simulation of water vaporization. For the desulfurization reaction, the experimental desulfurization efficiency was 75.03%, while the desulfurization efficiencies obtained by the Gidaspow and adjusted mesoscale drag models were 47.63% and 75.08%, respectively, indicating much higher accuracy of the latter technique.     

Real gas transport in tapered noncircular nanopores of shale rocks

A model for gas transport in tapered noncircular nanopores of shale rocks with integrating real gas effect, molecular kinetic, and transport behavior was presented. The proposed model is well validated with experimental and simulation data, including six kinds of gases, under different pressures, and temperatures. Results show that neglect of real gas effect results in the misleading transport conductance. The adsorbed gas transport ratio and the ratio of area occupied by adsorbed gas increase along the length of nanopore. Pore proximity induces the faster gas transport and omitting pore proximity leads to the enlargement of the adsorbed gas‐dominated region. Increasing taper ratio (ratio of inlet size to outlet size) and aspect ratio weakens real gas effect and lowers free gas transport. Moreover, it lowers the total transport capacity of the nanopore, and the tapered circular nanopore owns the greatest transport capacity, followed by tapered square, elliptical, and rectangular nanopores. © 2017 American Institute of Chemical Engineers AIChE J, 63: 3224–3242, 2017     

Multi-period design and planning model of shale gas field development

Long-term design and planning of shale gas field development is challenging due to the complex development operations and a wide range of candidate locations. In this work, we focus on the multi-period shale gas field development problem, where the shale gas field has multiple formations and each well can be developed from one of several alternative pads. The decisions in this problem involve the design of the shale gas network and the planning of development operations. A mixed-integer linear programming (MILP) model is proposed to address this problem. Since the proposed model is a large-scale MILP, we propose a solution pool-based bilevel decomposition algorithm to solve it. Results on realistic instances demonstrate the value of the proposed model and the effectiveness of the proposed algorithm.     

Synthesis of PEG‐functionalized poly(diphenylacetylene)s and their gas permeation properties

The polymerizations of 1‐(3‐methylphenyl)‐2‐(4‐trimethylsilyl)phenylacetylene ( 1a ) and 1‐(4‐methylphenyl)‐2‐(4‐trimethylsilyl)phenylacetylene ( 1b ) were carried out with TaCl₅‐n‐Bu₄Sn to give relatively high‐molecular‐weight polymers ( 2a and 2b ) (M_n > 5 × 10⁵). The obtained polymers were brominated by using benzoyl peroxide and N‐bromosuccinimide first, followed by substitution reaction of three types of polyethylene glycol. When diethylene glycol was used as a reagent on substitution reaction of meta‐substituted polymer, PEG‐functionalized poly(diphenylacetylene) with the highest content of oxyethylene unit [ 4a(2) ] was obtained, and the degree of substitution was 0.60. The degrees of substitution decreased to 0.15 and 0.08 when the polyethylene glycols with higher molecular weights were used. PEG‐substitution reaction to the para‐substituted polymers was difficult to proceed, and hence the degree of substitution was 0.18 even when diethylene glycol was used. The CO₂/N₂ separation factor of PEG‐functionalized polymer [ 4a(2) ] was as large as 28.8, although that of 2a was 7.41. The other PEG‐functionalized polymers also exhibited high CO₂ permselectivity, and their CO₂/N₂ separation factors were over 20. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

基于灵敏度分析的页岩气净化流程的模拟与优化

原料气中酸性气体与水等杂质的脱除净化是页岩气下游加工与利用的基础。应用化工流程模拟软件对页岩气脱酸与脱水流程进行模拟,旨为气体净化工业的实践提供理论与技术指导。在脱酸流程模拟中,采用灵敏度分析的方法讨论并优化了吸收剂再生进料位置、再生塔回流比等参数对脱酸流程的影响。脱水流程模拟中,提出了页岩气水含量与水露点的关联方法,为脱水标准的选取提供依据;采用汽提法解决了高浓度吸收剂的再生问题,使流程能够满足更高的脱水要求。     

CH4在PVDF中渗透行为及机理的分子模拟研究

采用巨正则蒙特卡洛法(GCMC)和分子动力学法(MD)相结合的方法模拟研究了典型气体CH4在聚偏氟乙烯(PVDF)中的吸附扩散行为,探讨了温度及压力对气体吸附扩散能力的影响,分析了CH4在PVDF中的吸附位点及扩散轨迹.模拟结果表明,CH4在PVDF中的溶解系数、渗透系数随温度的升高先增大后减小,随压力的升高而增大;扩...     

Effects of the cathode gas diffusion layer characteristics on the performance of polymer electrolyte fuel cells

Polymer electrolyte fuel cell (PEFC) electrodes were prepared by applying different porous gas diffusion half-layers (GDHLs) onto each face of a carbon cloth support, followed by the deposition of a catalyst layer onto one of these half-layers. The performance of PEFCs in H₂/air operation using cathodes with GDHLs presenting different characteristics were compared. The best result was obtained using cathodes with GDHLs having polytetrafluorethylene (PTFE) contents of 30 wt % in the gas side and 15 wt % in the catalyst side. This behaviour was explained in terms of a better water management within the cell.     

气固流化床介尺度结构形成机制及过滤曳力模型研究进展

气固流化床中,介于颗粒与宏观尺度间的复杂的时空多尺度结构（介尺度结构）将完全改变气固相间作用规律,加大了流态化系统调控及预测的难度。为此,需要构建考虑结构影响的相间本构关系。其中,曳力作为影响流态化动力学特征的主导因素,对其研究尤为重要。从结构产生演化的机制出发,概述结构影响曳力的机理,以模型构建流程的角度对结构和过滤两类模型进行总结,并重点综述过滤模型构建在提升准确性、有效性、通用性和考虑更多物理机制方面的最新进展。研究表明：提升模型通用性和考虑真实系统中更丰富的物理机制仍是建模中亟待解决的问题,结合结构演化机制理性建模和充分发挥机器学习数据分析处理优势或是曳力建模进一步发展的关键。