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1.
传统的煤层气动力学模型多建立在欧几里得基础上,难以描述煤层气孔隙结构的复杂性和形状的不规则性。为此,以分形理论为基础,通过引入煤层基质和裂缝的分形维数来刻画煤层气孔隙结构的复杂性和吸附特性,建立了双重分形介质渗流模型,采用Douglas-Jones预估-校正法对非线性方程组进行离散,获得了无限大地层和有限地层定产量生产时拟稳态吸附模型的差分方程,求得数值解。结果表明,Douglas-Jones预估-校正法可以有效解决这类非线性模型的求解问题,获得无限大地层定产量生产时变形双重分形介质模型的数值解;分析各种分形参数下的煤层压力动态,做出了典型压力曲线图。对无限大地层,初期分形维数对压力影响不大,后期分形维数越小,压力越高。对有限地层,初期分形维数的影响明显,且分形维数越大,压力越低。压力随分形指数的减小量呈现先增大后减小的趋势,在末期压力平稳趋向同一值。  相似文献   

2.
考虑煤层的双重介质特征和介质的分形特征,建立了考虑井筒储存和表皮效应影响的分形介质煤储层非平衡吸附、非稳态条件下的气体流动数学模型,并分别求得了无限大地层条件下中心一口井定产量生产时无因次井底压力的Laplace空间解析解和实空间上的数值解.给出了无因次井底压力及其导数随分形参数、无因次井筒储存系数以及表皮系数等变化的双对数曲线图.  相似文献   

3.
在考虑了煤层的分形特征和启动压力梯度影响的基础上,建立了无限大煤层中气体低速非达西流动的数学模型,并求得了量纲为一的井底压力的Laplace空间解析解,并根据数值求解结果绘制了典型的井底压力动态曲线。研究结果表明:在定产量生产的情况下,分形维数和量纲为一的启动压力梯度对早期井底压力动态无显著影响;在生产的中后期,由于受二者的影响,压力导数曲线上的径向流水平直线段消失;量纲为一的井储系数的影响主要表现在续流阶段,而吸附系数则主要影响煤基质向裂隙扩散的过渡阶段。  相似文献   

4.
一维流体饱和粘弹性多孔介质层的动力响应   总被引:3,自引:1,他引:2  
杨骁  张燕 《力学季刊》2005,26(1):44-52
本文研究了不可压流体饱和粘弹性多孔介质层的一维动力响应问题。基于粘弹性理论和多孔介质理论,在流相和固相微观不可压、固相骨架服从粘弹性积分型本构关系和小变形的假定下,建立了不可压流体饱和粘弹性多孔介质层一维动力响应的数学模型,利用Laplace变换,求得了原初边值问题在变换空间中的解析解,并利用Laplace逆变换的Crump数值反演方法,得到原动力响应问题的数值解。数值研究了饱和标准线性粘弹性多孔介质层的动力响应,分析了固相位移、渗流速度、孔隙压力及固相有效应力等的响应特征。结果表明,与不可压流体饱和弹性多孔介质相同,不可压流体饱和粘弹性多孔介质中亦只存在一个纵波,并且固相骨架的粘性对动力行为有显著的影响。  相似文献   

5.
黄军旗  刘慈群 《力学学报》1993,25(3):309-316
本文研究球对称弥散问题,模型中考虑了孔隙介质的微结构特征。这种微结构起着广义的吸附作用,在溶质的输运过程中有滞后效应。文中考虑了五种微结构模型,它们是均衡吸附模型,一阶线性动力吸附模型、板状、柱状和球粒结构模型。分别求得Laplace空间的解析解,用Stehfest的数值反演技术获得各种模型的溶质浓度分布,并对有关的影响因素进行了量值考查,对认识微结构模型的特性有帮助,可以作为地层排污、特殊条件下的石油开采及溶滤萃矿等工程设计的理论依据。  相似文献   

6.
湿润剂提高煤层注水效果的机理研究   总被引:2,自引:0,他引:2  
从煤层注水湿润煤体的机理出发,论述了用湿润剂溶液注入煤体,提高煤层注水效果的机理。分析了煤层的结构及渗透介质模型;从沟通大裂隙孔隙到死端孔隙及微孔隙,依次建立了数学模型。煤层注水试验和现场测试验证了湿润剂提高煤层注水效果的机理。  相似文献   

7.
作为典型的致密多孔介质,煤岩储层已被证实存在启动压力梯度.根据煤层气垂直裂缝井的双线性流动机制,综合考虑启动压力梯度和井筒储存效应的影响,建立了一个新的低渗透煤层气有限导流垂直裂缝井双线性流动数学模型,采用Laplace变换和Stehfest数值反演方法对数学模型进行了求解,并分析了无因次启动压力梯度等参数对无因次井底压力及其导数曲线的影响规律.分析结果表明:典型的低渗透煤层气垂直裂缝井双线性流动曲线可划分为早期续流段、双线性流段、煤层线性流段、过渡流段和煤层边界线性流段5个特征阶段,其中由于启动压力梯度存在的影响,无因次井底压力及其导数曲线自煤层线性流段开始出现明显上翘,且启动压力梯度值越大,曲线上翘趋势越明显;此外,煤层边界线性流段呈现为单位斜率的直线,而非1/2斜率的线性流段直线.这些结果表现出启动压力梯度对低渗透煤层气垂直裂缝井双线性流动的影响,可用于指导现场煤层气井试井分析.  相似文献   

8.
岩土介质的分形孔隙和分形粒子   总被引:26,自引:3,他引:23  
谢和平 《力学进展》1993,23(2):145-164
岩土介质是晶粒状材料,存在大量的孔隙。这些孔隙的存在严重地影响岩土介质的力学、物理和化学性能。大量的研究表明,岩土介质的孔隙几何从原子尺度到晶粒尺寸范围内均表现出分形特征。目前分形几何已被广泛应用来研究岩土的孔隙率,输运特性和渗透性等等。本文从5个方面来讨论岩土介质的分形孔隙和分形粒子:①分形几何简介;②孔隙介质的分形模型;③岩土介质的分形孔隙特性和它们的分形量测方法;④岩土的分形粒子;⑤水土保持估计中的分形毛细管模型。  相似文献   

9.
本文采用双重孔隙介质模型和非线性二项式渗透定律,对一维问题推导了溶洞裂缝-孔隙介质中二相驱替问题的基本方程,并采用特征线方法求得了数值解,通过和线性情况比较,揭示了非线性效应和溶洞裂缝-孔隙介质中水驱油的基本规律。  相似文献   

10.
大理岩微孔隙演化的分形特征   总被引:3,自引:0,他引:3  
本文利用压汞技术测定了大理岩随应力变化的微孔隙演化过程,根据孔隙介质的分形模型,计算了大理岩微孔隙演化过程中的分维变化。研究表明:孔隙岩体确实是一个分形结构,孔隙体积分维随外载增加而增大。  相似文献   

11.
Desorption of gas from coal matrix alters the pore volume of fracture network. Consequently, cleat porosity and permeability of reservoir changes as pressure depletes. The method of standard pressure analysis calculations produces incorrect results in the case of coalbed methane reservoirs producing under dominant matrix shrinkage effect. The change in cleat porosity and permeability due to shrinkage of coal matrix following gas desorption with pressure depletion invalidates the underlying assumptions made in the derivation of diffusivity equation. Consequently, equations of pseudo-steady state commonly used in conventional reservoirs no longer remain valid as the porosity and permeability values change with pressure depletion. In this paper, effort has been made to describe pseudo-steady-state flow in coalbed methane reservoirs in the form of a new equation that accounts for pressure dependency of cleat porosity and permeability due to shrinkage of coal matrix. The concept of Al-Hussainy et al. (1966) has been extended to define a new pseudo-pressure function which assimilates within itself the pressure dependence of porosity and permeability Palmer and Mansoori (1998). Equation has been used to relate the cleat porosity with pressure. The equation-based computational method suggested in this paper finds its usefulness in estimating average reservoir pressure for any known flowing bottom hole pressure and thus reducing the frequency of future pressure buildup tests. The new equation is also useful in predicting reservoir pressure under the situation when coal matrix shrinks below desorption pressure. The equation used in the computational method has been validated with the help of numerical simulator CMG-GEM.  相似文献   

12.
通过对美国Antrim页岩气藏及一些别的低阶煤层的研究表明,在基质颗粒中也有相当一部分自由气存在。本文建立了低阶煤层中单相煤层气三孔双渗流动的试井模型,并获得了模型在拉氏空间上的解析解以及模型的数值解,讨论了储层外边界条件、弹性储容比、窜流系数以及吸附系数等参数对于压力动态响应的影响。结果表明:外边界条件决定着早期过渡段出现的早晚;窜流系数和弹性储容比影响窜流阶段出现的早晚;而吸附系数对晚期过渡段影响明显。  相似文献   

13.
Based on Fick’s law in matrix and Darcy flow in cleats and hydraulic fractures, a new semi-analytical model considering the effects of boundary conditions was presented to investigate pressure transient behavior for asymmetrically fractured wells in coal reservoirs. The new model is more accurate than previous model proposed by Anbarci and Ertekin, SPE annual technical conference and exhibition, New Orleans, 27–30 Sept 1998 because new model is expressed in the form of integral expressions and is validated well through numerical simulation. (1) In this paper, the effects of parameters including fracture conductivity, coal reservoir porosity and permeability, fracture asymmetry factor, sorption time constant, fracture half-length, and coalbed methane (CBM) viscosity on bottomhole pressure behavior were discussed in detail. (2) Type curves were established to analyze both transient pressure behavior and flow characteristics in CBM reservoir. According to the characteristics of dimensionless pseudo pressure derivative curves, the process of the flow for fractured CBM wells was divided into six sub-stages. (3) This paper showed the comparison of transient steady state and pseudo steady state models. (4) The effects of parameters including transfer coefficient, wellbore storage coefficient, storage coefficient of cleat, fracture conductivity, fracture asymmetry factor, and rate coefficient on the shape of type curves were also discussed in detail, indicating that it is necessary to keep a bigger fracture conductivity and fracture symmetry for enhancing well production and reducing pressure depletion during the hydraulic fracturing design.  相似文献   

14.
Accurate prediction of coal׳s creep behavior is of great significance to coalbed methane extraction. In this study, taking into account the visco-elastic–plastic characteristics and the damage effect, a fractional non-linear model is proposed to describe the creep behavior of coal. The constitutive and creep equations of the proposed fractional non-linear model are derived via the Boltzmann superposition principle and discrete inverse Laplace transform. Furthermore, uniaxial creep tests under different axial stress conditions were carried out to validate the proposed model. It is found that the present model can describe the experimental data from creep tests with better accuracy than classical models. Particularly, the present model can predict the accelerating creep deformation of coal which classical models fail to reproduce. Finally, the parametric sensitivity analysis is performed to investigate the effects of model parameters on the creep strain. It is verified that the introduction of fractional parameters and damage factor in the present model is essential to accurate prediction of the full creep stage of coal.  相似文献   

15.
The deep-mining coal seam impacted by high in situ stress, where Klinkenberg effects for gas flow were very obvious due to low gas permeability, could be regarded as a porous and tight gas-bearing media. Moreover, the Klinkenberg effects had a significant effect on gas flow behavior of deep-mining coal seam. Based on the gas flow properties of deep-mining coal seams affected by in situ stress field, geothermal temperature field and geo-electric field, a new mathematical model of coalbed gas flow, which reflected the impact of Klinkenberg effects on coalbed gas flow properties in multi-physical fields, was developed by establishing the flow equation, state equation, and continuity equation and content equation of coalbed gas. The analytic solution was derived for the model of one-dimensional steady coalbed gas flow with Klinkenberg effects affected by in situ stress field and geothermal temperature field, and a sensitivity analysis of its physical parameters was carried out by comparing available analytic solutions and the measured values. The results show that the analytic solutions of this model of coalbed gas flow with Klinkenberg effects are closer to the measured values compared to those without Klinkenberg effects, and this model can reflect more accurately gas flow of deep-mining coal seams. Moreover, the analytic solution of this model is more sensitive to the change of Klinkenberg factor b and temperature grad G than depth h.  相似文献   

16.
In-depth understanding of how methane diffuses in porous media like coal is critical for enhanced coalbed methane recovery and coal seam methane drainage. However, the classic unipore gas diffusion model can only describe methane diffusion behavior in coal at the early time diffusion stage. Describing the whole methane diffusion behavior in coal has not been reasonably addressed in the coalbed methane field. Considering the large surface-to-volume ratio of coal, the authors proposed a time-dependent gas diffusion model to describe the whole diffusion process. This work first proposed a power–law relationship between diffusion coefficient and time according to previous studies of the time-dependent gas diffusion process in porous media. Then, both the analytical solution and its approximation solution for the time-dependent gas diffusion model were derived. Six methane diffusion tests in crushed coal were conducted to validate the proposed model under different pressures (0.5, 1.5, 2.5 MPa) and temperatures (20 and \(30\,{^{\circ }}\hbox {C}\)). Modeling results show that the time-dependent gas diffusion model is superior to the classic unipore gas diffusion model for describing the whole methane diffusion process in coal. Increasing temperature always accelerates methane diffusion in coal; the higher the temperature the larger the diffusion coefficient.  相似文献   

17.
In the process of coal seam fracturing with liquid nitrogen (LN2), the change of coal pore structure has an important influence on the efficiency of coalbed methane (CBM) extraction. The nano-scale pore size distribution (PSD) in coal particles before and after freezing with LN2 are experimentally studied in this work. Coal samples are collected from four coal mines, where coal and gas outburst accidents have occurred. Small angle X-ray scattering technology (SAXS) and scanning electron microscopy (SEM) are used to study the pore structure changes of coal samples quantitatively and qualitatively. It is found that the scattering intensity of coal samples increases after freezing. The PSD of all samples significantly changes in the range of 0.8–7 nm, showing new pore spaces in 0.8–4 nm and fewer pores in the 4–7 nm range. Both the pore fractal dimension and the radius of gyration of coal samples increase after freezing and are mainly affected by the changes in pores and the anisotropy of the coal matrix. Crack expansion and pore connections are observed in the surface structure of the coal sample using SEM. This study provides a better understanding of the nano-scale mechanism of coal seam fracturing with LN2 for the prevention of coal and gas outbursts.  相似文献   

18.
A simple and effective experimental method is proposed to simulate coal fines migration through the proppant pack; such migration inevitably occurs during the process of fracturing fluid flowback or dewatering and gas production in coalbed methane (CBM) reservoirs. The damage to conductivity caused by coal fines migration in the pack and the factors affecting such migration are analyzed. A dispersion agent of coal fines applicable to hydraulic fracturing in CBM is optimized, consequently solving the problem of coal fines aggregation and retention in the proppant pack. Discharging coal fines with water or water-based fracturing fluid from the proppant pack can be difficult because of the adsorption and hydrophobicity of coal fines. Thus, coal fines are likely to aggregate and be retained in the proppant pack, thereby resulting in pore throat plugging, which causes serious damage to fracture conductivity. Two percent coal fines can reduce propped fracture conductivity by 24.4 %. The mobility and retention of coal fines in the proppant pack are affected by proppant size, proppant type, flowback rate, and coal fines property. When flowback rate exceeds the critical value, coal fines can be discharged from the pack, consequently reducing damage to propped fracture conductivity. More importantly, the steady discharging of coal fines requires steady dewatering and gas production to avoid flow shock, which causes pressure disturbance to drive coal fines in a remote formation. The optimized dispersant FSJ-02 employed in this paper can effectively change the wettability and surface potential of coal fines to improve their suspension and dispersion in water-based fracturing fluid. The recovery rate of coal fines increased by 31.5 %, whereas conductivity increased by 13.3 %.  相似文献   

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