基于分形理论的高煤阶煤岩渗透率计算方法研究与应用

为了提供有效的煤岩渗透率计算斱法,基于分形理论推导了煤样渗透率计算模型,提出了相应参数的获取斱法,基于高压压汞实验获得的毛管压力数据和实验测得的相应煤样的渗透率数据验证了计算斱法的正确性,并基于该斱法利用数值模拟的斱法分析了煤样渗透率的主要影响因素。结果表明,分形理论的煤岩渗透率计算斱法能够有效预测煤岩渗透率,平均误差仅为6.84%;煤岩分形维数、迂曲度和最大孔隙半径对渗透率具有重要影响,煤岩渗透率随着分形维数和迂曲度增加而降低,随最大孔隙半径增加而增加。     

海上低渗致密砂岩气藏渗流模型研究

结合压汞曲线来研究砂岩储层的分形维数,利用实验说明了致密气藏存在分形特性,通过推导计算了致密气藏分形维数,对于复杂的微小孔隙发育的砂岩孔隙结构,分形维数接近3.基于实验证实分形的基础上,考虑基质孔隙和裂缝存在分形特性,并考虑到致密气藏的应力敏感性,基于致密气在纳米级孔隙中的非达西流动特点,建立了新的分形致密气藏渗流模型,通过对模型进行求解的基础上研究了具有分形特性的致密气藏渗流规律.绘制并分析了不同参数影响下的压力动态典型曲线.通过分析表明,基质和裂缝分形参数都对压力动态产生影响,但影响的流动时期和阶段不同.传统的气藏模型是本文所建模型的特例.     

用分形理论研究低渗储层孔隙结构

储集层岩石的孔隙结构非均质性对于油气的渗流规律以及水驱油效率都具有重要的影响。利用分形理论对孔隙结构的非均质性进行研究。结果表明,分形维数不同孔隙结构不同,所研究的储集层具有单一分形（分形维数2.690 7～2.814 0）和分段分形特征（分形维数2.414 8～2.995 2）;以分形维数为基础,可以根据孔喉渗透率贡献判断孔隙结构的非均质性和复杂程度。     

准噶尔盆地永进油田特低渗储层分类评价研究

针对准噶尔盆地永进油田超深层、特低渗储层渗滤能力差,传统的储层分类评价难以细分界限的特点,引入毛管曲线分形维法和BP神经网络方法。储层岩石的孔隙结构是一种分形结构,可以用分形维数来定量描述其复杂程度。通过建立毛管压力曲线和孔隙大小分布的分形几何模型,计算了孔隙结构的分形维数,定量描述孔隙结构的复杂程度;用BP神经网络方法,经过反复实验和分析,输入5个节点数,即分形维和四条测井曲线系列(包括自然伽马、声波时差、深侧向和浅侧向电阻率),输出1个节点数,即一条深度连续的分形维曲线。网络预测值与实验值精度基本一致,根据上述方法原则求取了各井的分形维曲线,用以储层的精细分类及有效性评价。     

分形特征在孔渗计算中应用的意义研究

储层孔隙与喉道空间分布具有统计自相似性特点,孔隙结构特征也可以用分形几何学进行描述。与其他方法相比,岩石微观孔隙结构被我们用分形的方法看作复杂无规律的整体进行研究,这样,得到的计算结果更符合真实情况。本文基于压汞实验资料,计算出样品的孔隙结构分形维数。经过深入研究发现,孔隙结构分形维数与储层参数之间具有一定相关性,基于孔隙结构分形维数的储层物性参数建模能够取得较好效果。研究表明基于压汞资料所求取的,孔隙结构分形维数可为储层孔隙结构微观非均质性研究提供有效方法,并为进一步储层评价奠定基础。     

基于分形学的膜面滤饼特性研究进展

膜污染问题限制了膜分离技术在实际工程中的广泛应用。从分形解析的角度深入探讨混凝-膜过滤过程中滤饼层的微观结构对控制膜污染情况至关重要。总结和回顾了运用分形理论表征滤饼层重要性质参数孔隙率、比阻、渗透率研究的前沿动态,对絮体特性和滤饼层特性两者内在关系进行分析评述,以期为混凝-膜过滤工艺优化提供参考。     

孔隙分布对分形泡沫金属基相变材料传热特性的影响

基于分形理论,采用Sierpinski分形结构来模拟分形泡沫金属的孔隙结构。以泡沫金属为基体,孔隙中填充相变材料,通过数值计算比较了相同孔隙率和分形维数但不同孔隙结构分布规律的泡沫金属基相变材料在恒热流边界条件下的传热特性差异,得到了在传热过程中相变材料的相变率随时间变化及其相场分布情况云图。结果表明：当泡沫金属存在开口孔且所在位置处于热流边界时,孔隙中相变材料的传热速率明显大于不存在任何孔隙处于热流边界的情况;当泡沫金属不存在孔隙处于热流边界时,随着泡沫金属比表面积的增大,孔隙中相变材料传热速率增大;且分形体的分形级数越高,孔隙分布规律对其传热性能的影响程度越大。     

疏水缔合聚合物HT-1在多孔介质中的渗流类型

利用实验自制平板夹砂渗流装置,研究了疏水缔合聚合物在两级串联平板夹砂渗流模型中渗流。结果表明：疏水缔合聚合物在两级串联多孔介质中存在三类不同的渗流类型,与孔隙介质的渗透率相关;第I类：当渗透率大于1.8 μm2时,表现为阻力系数在流动方向上相等的渗流特性;第II类：当渗透率等于1.8 μm2时,表现为阻力系数在流动方向上增大的渗流特性;第III类：当渗透率小于1.8 μm2时,表现为阻力系数在流动方向上减小的渗流特性。通过单级与两级串联平板夹砂渗流模型中渗流实验的对比,推断出第II类和第III类渗流类型中阻力系数的差异是由聚集体变化造成的。并采用单级与两级串联微孔滤膜过滤实验和动态光散射实验研究了渗流过程中聚集体尺寸变化,验证出第Ⅱ类和第Ⅲ类渗流类型中阻力系数的差异是由疏水缔合聚合聚集体尺寸在串联平板夹砂模型中发生变化造成的。     

西泉103井区火山岩储层特征研究

火山岩油藏具有相对复杂的渗流规律,明确其储层条件下的渗流机理有利于制定合理、有效的开发方案。通过压汞、核磁共振等多个实验,综合描述了西泉地区火山岩的储层物性特征、孔吼结构特征。实验表明:西泉103井区孔隙类型以溶孔为主,其次为气孔,裂缝发育较少,孔隙分布以小孔隙为主,孔隙度高,渗透率低,孔喉特征表现为微-小吼道,束缚水饱和度普遍较高。研究结果对于该区域火山岩油气藏勘探开发有一定指导意义。     

DST测试资料在储层有效渗透率解释方面的应用

为满足数值模拟对油气储层有效渗透率准确解释的要求;通过岩心分析化验资料和测井解释资料建立岩心规模孔隙渗透率模型,准确求取岩心规模孔隙渗透率;再引入DST测试分析资料,建立DST测试渗透率和岩心规模孔隙渗透率的关系模型,即多重介质渗透率模型,从而得出能够反映储层真实渗流特征的多重介质渗透率。油藏数值模拟计算和实际生产动态证实多重介质渗透率较孔隙渗透率可以更为真实地反映储层流体的渗流特征。在类似储层的渗透性评价中该评价方法值得推广和应用。     

气压过滤的成饼动力学及其滤饼的分形结构

用自制的实验室型气压过滤机并结合滤饼内部结构的测试,研究了气压过滤的成饼动力学及其滤饼结构的分形特征。结果表明,气压过滤条件下,虽然过滤压差较大,但成饼阶段仍遵循Darcy定律;气压过滤的滤饼结构为一分段Sierpinski分形,其分维数值介于1.775～1.885之间。     

分形理论在多孔介质渗透性能的研究

对分形理论在多孔介质的结构和渗透性能的研究进行了综述,并且提出了分形理论和多孔介质性质在研究膜过滤中形成的沉积层的结构和渗透性能的可行性。     

Experimental study of cake formation on heat treated and membrane coated needle felts in a pilot scale pulse jet bag filter using optical in-situ cake height measurement

Pulse-jet bag filters are frequently employed for particle removal from off gases. Separated solids form a layer on the permeable filter media called filter cake. The cake is responsible for increasing pressure drop. Therefore, the cake has to be detached at a predefined upper pressure drop limit or at predefined time intervals. Thus the process is intrinsically semi-continuous. The cake formation and cake detachment are interdependent and may influence the performance of the filter. Therefore, understanding formation and detachment of filter cake is important. In this regard, the filter media is the key component in the system. Needle felts are the most commonly used media in bag filters. Cake formation studies with heat treated and membrane coated needle felts in pilot scale pulse jet bag filter were carried out. The data is processed according to the procedures that were published already [Powder Technology, Volume 173, Issue 2, 19 April 2007, Pages 93-106]. Pressure drop evolution, cake height distribution evolution, cake patches area distribution and their characterization using fractal analysis on different needle felts are presented here. It is observed that concavity of pressure drop curve for membrane coated needle felt is principally caused by presence of inhomogeneous cake area load whereas it is inherent for heat treated media. Presence of residual cake enhances the concavity of pressure drop at the start of filtration cycle. Patchy cleaning is observed only when jet pulse pressure is too low and unable to provide the necessary force to detach the cake. The border line is very sharp. Based on experiments with limestone dust and three types of needle felts, for the jet pulse pressure above 4 bar and filtration velocity below 50 mm/s, cake is detached completely except a thin residual layer (100-200 μm). Uniformity and smoothness of residual cake depends on the surface characteristics of the filter media. Cake height distribution of residual cake and newly formed cake during filtration prevails. The patch size analysis and fractal analysis reveal that residual cake grow in size (latterly) following regeneration initially on the base with edges smearing out, however, the cake heights are not leveled off. Fractal dimension of cake patches boundary falls in the range of 1-1.4 and depends on vertical position as well as time of filtration. Cake height measurements with Polyimide (PI) needle felts were hampered on account of its photosensitive nature.     

高温陶瓷过滤管性能退化建模及实时寿命预测

高温陶瓷过滤管由内部孔径较大的支撑体和外部孔径较小的过滤膜双层结构构成,在实际应用中,存在大量粒径较小的粉尘颗粒,会穿过过滤膜沉积到支撑体内部,脉冲反吹无法有效清除. 因支撑体内颗粒沉积及管壁外残余粉尘层不断压缩,使陶瓷过滤管渗透率不断下降,残余压降逐渐增加。本工作基于高温陶瓷过滤管壁内颗粒沉积特性及残余粉尘层压缩不可直接观测的特点,结合贝叶斯估计理论,利用过滤管运行期间采集的残余压降数据,提出一种基于状态空间模型的过滤管性能退化建模方法。该方法能融入最新采集到的残余压降数据,实时对模型参数进行更新,可对陶瓷过滤管的剩余寿命进行实时预测,同时对陶瓷过滤管剩余寿命的失效概率密度分布及陶瓷过滤管的退化状态变化率进行预测。对某高温试验装置及壳牌煤气化装置中的陶瓷过滤管残余压降分析表明,预测剩余寿命准确率随残余压降数据增加而逐渐增加,后期预测准确率高于95%,且陶瓷过滤管退化状态变化率逐渐变小,与陶瓷过滤管残余压降前期增加快后期增加慢的现象一致。     

颗粒群的体积分维数对过滤性能的影响

从理论上证明了颗粒群的体积分维数的物理含义,结果表明颗粒群的体积分维数可定量描述颗粒群的粒度分布宽度,准确反映了颗粒群填充三维空间的能力,并通过试验研究了颗粒群的体积分维数对滤饼孔隙率及比阻的影响规律。     

操作温度对褶皱型不锈钢编织型过滤器阻力特性的影响

Effect of working temperature on the resistance characteristic including the permeability coefficient and the pressure drop evolution of a pleated stainless steel woven filter with a nominal pore size of 0.5 μm has been studied. The permeability coefficient was obtained based on the pressure drop data and the Darcy’s law. In three filtration experiments, pure carbon dioxide at 283 K, nitrogen at 85 K and liquid helium at 18 K are adopted, respectively. It is found that the permeability coefficient decreases at the working temperature due to the cold shrink of the filter element at cryogenic temperature. Then, two kinds of feed slurries, mixture of liquid nitrogen and solid carbon dioxide at 85 K, and mixture of liquid helium and solid nitrogen at 18 K, flow into the filter cell. The solid particles are deposited on the filter surface to form a filter cake and the purified liquid flows through the filter. It is found that the pressure drop evolution shows the same trend on these two temperatures, which can be divided into three stages with high filtration efficiency, indicating the feasibility of the filter for cryogenic application. However, variant cake resistances are obtained, which is resulted from the different interactions between solid particles in the feed slurry at lower working temperature.     

Optical in-situ measurement of filter cake height during bag filter plant operation

A pilot scale jet pulsed bag filter test facility is operated at conditions similar to those of the industrial bag filters. The facility is equipped with a stereo vision based optical system for in-situ cake height distribution measurements on the bag filter surface. Experimental data are presented and data evaluation procedures are discussed to elaborate the features of the measuring system.The results show that the cake height distribution becomes narrower towards the end of filtration cycles. A steep pressure drop rise is observed at the start of a filtration cycle in the absence of re-attachment and a non-uniform bag cleaning, which may be attributed to different cake properties. The specific cake resistance remains constant over the linear part of the pressure drop curve indicating a non-compressible cake formation.The analysis of residual cake patches shows a large number of small sized cake patches and a few large sized cake patches on the filter surface. The cake patch size increases with the cake formation. The fractal analysis of patches boundary indicates preferential cake formation at the boundary of the residual cake patches shortly after regeneration.     

Correlations between pore structure parameters and gas permeability of corundum porous materials

Corundum porous materials with different contents of calcium hexaluminate formed in situ were prepared using pure calcium aluminate cement as the calcium source. The surface fractal dimensions of the porous materials were calculated based on the experimental data of mercury intrusion. Correlations between pore structural parameters and the permeability coefficients k₁ and k₂ of the porous materials were then studied based on the grey system theory. The results showed that pores in the corundum porous materials have great fractal characteristics. The surface fractal dimension was a significant pore structural parameter that reflected the complexity of pore shape, pore surface, and pore-size distribution, which had the maximum correlation coefficient with the permeability of this type of porous materials. The apparent porosity and pore-size distribution had relatively high correlation coefficients to the permeability as well. Increasing the apparent porosity and the volume percentage of larger pores, and decreasing the volume percentage of smaller pores all benefited the permeability of the porous materials. In addition, the mean pore size and median pore size showed lower correlation coefficients to the permeability—especially for porous materials with a wide pore-size distribution.