Magma yield stress and permeability: Insights from multiphase percolation theory

Magmas often contain multiple interacting phases of embedded solid and gas inclusions. Multiphase percolation theory provides a means of modeling assemblies of these different classes of magmatic inclusions in a simple, yet powerful way. Like its single phase counterpart, multiphase percolation theory describes the connectivity of discrete inclusion assemblies as a function of phase topology. In addition, multiphase percolation employs basic laws to distinguish separate classes of objects and is characterized by its dependency on the order in which the different phases appear. This paper examines two applications of multiphase percolation theory: the first considers how the presence of bubble inclusions influences yield stress onset and growth in a magma's crystal network; the second examines the effect of bi-modal bubble-size distributions on magma permeability. We find that the presence of bubbles induces crystal clustering, thereby 1) reducing the percolation threshold, or critical crystal volume fraction, ?_c, at which the crystals form a space-spanning network providing a minimum yield stress, and 2) resulting in a larger yield stress for a given crystal volume fraction above ?_c. This increase in the yield stress of the crystal network may also occur when crystal clusters are formed due to processes other than bubble formation, such as heterogeneous crystallization, synneusis, and heterogeneity due to deformation or flow. Further, we find that bimodal bubble size distributions can significantly affect the permeability of the system beyond the percolation threshold. This study thus demonstrates that larger-scale structures and topologies, as well as the order in which different phases appear, can have significant effects on macroscopic properties in multiphase materials.     

孔隙裂隙双重介质的三维逾渗数值模拟研究

基于三维孔隙介质的逾渗模型,首次把裂隙这一重要的渗透通道引入到三维逾渗研究中,提出了孔隙裂隙三维逾渗的研究方法,并建立了孔隙裂隙双重介质三维逾渗模型,这一模型的建立使得逾渗理论的研究成果可以被应用到更多的领域中,如煤体、岩体等。基于VC++6.0开发了孔隙裂隙双重介质三维逾渗模拟软件,模拟研究了双重介质的逾渗规律,模拟研究表明：裂隙的存在在很大程度上提高了介质的逾渗概率,使孔隙裂隙双重介质的逾渗规律明显不同于孔隙介质;随孔隙率、裂隙分形维数、裂隙数量分布初值由小到大逐渐增长,必然发生逾渗转变的自然现象。     

石佛寺水库改性粉细砂筑坝试验研究

采用室内试验和现场原型试验,对辽河石佛寺水库库区内掺入水泥后粉细砂的特性进行了研究。试验结果表明,随着水泥掺入量的增加,粉细砂的凝聚力和内摩擦角增大,渗透系数减小。当水泥的掺入量为2 % 时,抗剪强度指标和渗透系数已明显改善,而且在最不利的情况下满足对渗透变形的要求。粉细砂掺入水泥后,其性能得到了很大改善,用于修筑拦河主坝是完全可行的。     

RBFNN模型在渗透系数反演中的应用

针对经典的BP网络存在的一些缺陷,采用了径向基函数神经网络（RBFNN）。在相同的收敛条件下,用RBFNN和经典算法的BP网络进行了比较,表明前者具有优越性。在工程实例中,基于人工神经网络的非线性特点,在三维渗流有限元的基础上,利用RBFNN反演了大坝的渗透系数。并利用反演结果进行渗流场分析,水头预报值也有很高的精度,说明反演结果是正确的,从而,验证了RBFNN应用于反演分析中的可靠性。     

油田高含水期基于微观渗流机理的宏观岩心水驱油数值模拟研究

建立地层孔隙网络模型描述微观孔喉特征,利用逾渗方法计算基于微观渗流机理的相对渗透率曲线,并将之应用到数值模拟计算中,给出考虑微观渗流特征的方程,并进行数值求解,得到地层中流体分布特征。实例分析表明该方法可以得到基于微观特征的剩余油分布数量和形式,为调剖堵水、化学驱提供技术参数,实现微观渗流机理与宏观计算的结合。     

基于Hydrus-1d模型的农田SPAC系统水分通量估算——以山西省运城市董村农场为例

农田SPAC系统水分通量的研究对提高农业用水效率,缓解我国的水资源短缺现状具有重要作用.本文利用HydruS-1d模型,以山西省运城市董村农场为例,估算了研究区三种主要农作物(夏玉米、棉花和冬小麦)的农田水分通量.结果表明,在模拟期内,夏玉米、棉花和冬小麦的作物蒸腾占蒸散发(T/ET)的比值分别为84.7%、71.6%...     

地下空间逾渗与裂缝属性的关系分析

裂缝连通性评价是地下空间研究的重要内容。逾渗分析是研究裂缝网络连通性的一种有效手段。裂缝网络逾渗临界值多使用裂缝间接表征参数(如分形维数)来确定,但存在裂缝网络连通性不同却有相同间接表征参数的情况,这降低了预测的可靠性。为避免此类问题并更加准确快速地表征裂缝网络的连通性,文章在构建逾渗临界值方程时,摒弃了间接参数简化的方式,使用裂缝直接表征参数(如裂缝数量、长度等)进行非线性拟合。通过二维数值模拟建立不同参数的离散裂缝网络模型,分析逾渗低、中、高概率临界条件与裂缝直接表征参数的关系,建立逾渗临界条件预测方程,并对方程在不同尺度研究区的应用进行了讨论和验证。结果表明：预测方程可有效地预测不同概率的逾渗临界值。同时文章在预测方程的基础上,建立了裂缝网络连通性评价标准,这对于裂缝发育地区的地下空间评价工作具有一定的指导和借鉴意义。     

Asperity models and characteristic earthquakes

Summary. An asperity model is presented, including the effects of coupled elementary faults. This coupling is introduced by way of percolation theory. We postulate that the elementary faults have a typical size, whose dimensions are of order 0.3–0.4 km, and two kinds of characteristic earthquakes are obtained, one in the low magnitude range involving the rupture of a single elementary fault, and one in the high magnitude range involving a percolated cluster of faultlets, whose dimensions are proportional to the total fault. The magnitude–frequency relation of this model is constructed and the Gutenberg–Richter relation is obtained with a b value of 1 in the range of intermediate earthquakes. A relative enhancement in the probability of occurrence of large earthquakes is also observed. This effect is associated with 'characteristic earthquakes', whose magnitudes are related to the size of the active fault. Possible premonitors are discussed.     

Delineation of Microscale Regimes of Fully-Developed Drainage and Implications for Continuum Models

Despite significant progress made in recent years, a fundamental understanding of immiscible displacements at the macroscale is lacking. In this paper we use a version of percolation theory, based on invasion percolation in a gradient, to connect drainage processes at the pore-network scale with the displacement at the macroscale. When the mobility ratio M is sufficiently small, the displacement is stabilized and can be described by invasion percolation in a stabilizing gradient. In the opposite case, it has common features with invasion percolation in a destabilizing gradient. A diagram delineating the regimes of fully developed drainage is developed. The transition between stabilized displacement and fingering is controlled by the change of the sign of the gradient of the percolation probability, and the transition boundary is described by a scaling law involving the capillary number and the viscosity ratio. We review recent work for random networks and extend the method to correlated pore networks. As the regimes of stabilized displacement are also those for which conventional theories (such as the Buckley–Leverett equation) are expected to apply, the phase diagram helps to delineate their validity.     

鄂尔多斯盆地姬塬地区长6储层渗流特征

对鄂尔多斯盆地姬塬地区长6储层特征、微观渗流特征及影响因素进行综合研究,为开发前期评价提供科学依据。以铸体薄片、扫描电镜等分析化验资料为基础,应用恒速压汞、核磁共振等储层评价新方法对岩石类型、孔隙结构进行分析。研究表明,该区长6储层物性较好,粒间孔发育,储层孔隙结构好,以小孔、微细喉为主,可动流体饱和度高,渗流能力强,有利于高效开发。储层孔隙结构、成岩相及储层润湿性是影响相渗特征的重要因素。