低渗透油藏渗流启动压力理论计算方法

油层中流体必须克服一定压力后才能流动,这种压力即为流体渗流时的启动压力．本文从流变学原理出发,推导出低渗透油藏流体渗流启动压力的理论计算公式。该方法计算简便,易于科技人员掌握使用,从而为油田开发部署提供一定依据。     

Percolation on grain boundary networks: Application to fission gas release in nuclear fuels

The percolation behavior of grain boundary networks is characterized in two- and three-dimensional lattices with circular macroscale cross-sections that correspond to nuclear fuel elements. The percolation of gas bubbles on grain boundaries, and the subsequent percolation of grain boundary networks is the primary mechanism of fission gas release from nuclear fuels. Both radial cracks and radial gradients in grain boundary property distributions are correlated with the fraction of grain boundaries vented to the free surfaces. Our results show that cracks surprisingly do not significantly increase the percolation of uniform grain boundary networks. However, for networks with radial gradients in boundary properties, the cracks can considerably raise the vented grain boundary content.     

Percolation theory in SOFC composite electrodes: Effects of porosity and particle size distribution on effective properties

A percolation model, accounting for polydispersion of powders and presence of pore formers (i.e. porosity), is presented to predict effective properties of composite electrodes for solid oxide fuel cells, such as the three-phase boundary length and the mean hydraulic radius. Porosity affects both numbers of contacts (so probabilities of connection) and number of particles per unit volume. Both these effects, together with granulometric distribution, are accounted for the estimation of effective properties. As a consequence, the theory can predict numbers of contacts, coordination numbers and therefore effective properties of the electrode for multicomponent polydisperse mixtures.Model simulations show that the three-phase boundary length sharply decreases as porosity increases while the effects of polydispersion of powders are less pronounced, although significant, suggesting that these features should be considered in SOFC electrode models.     

Effect of CdSe/P3HT composition on electrical and structural properties of bulk hetero-junction solar cell active layer

The use of inorganic nano-semiconductor/polymer blend as the active layer for organic bulk hetero-junction solar cell is an alternative to change and improve the device characteristics and performance. Effects of CdSe/P₃HT composition in the blend and its loading amount in the solvent on the electrical and structural properties of active layers formed were investigated. The results of atomic force microscopy study indicated that the surface roughness of composite active layer could be controlled below 10 nm for the entire range of composite loading amount investigated in this study. The transmission line method experiments have demonstrated that the electrical percolation pathways could be developed at the critical loading amount of CdSe/P₃HT composite, resulting in the abrupt decrease of sheet resistance and significant increase in the power conversion efficiency of ITO/PEDOT:PSS/(CdSe/P₃HT)/Al solar cell.     

Combined micro-scale and macro-scale modeling of the composite electrode of a solid oxide fuel cell

The design of a cathode inter-layer is important to the high performance of a solid oxide fuel cell (SOFC). In this paper, the processes of electrochemical reactions, electronic and ionic conductions and gas transports in an SOFC are discussed in detail. An analysis shows that the current conduction and electrochemical processes can be replicated by an equivalent circuit model. A corresponding macro-scale model using the Butler-Volmer equation for electrochemical reactions, Ohm's law for current conduction and the Dusty-gas model for gas transport is described. A percolation theory based micro-model is used to obtain the effective electrode properties in the macro-model from the microstructure parameters of the porous electrode. Experimental I-V relations can be accurately accounted for by the proposed theory. The macro- and micro-models are then combined to systematically examine the effects of various parameters on the performance of a composite cathode inter-layer. The examined parameters include the thickness, effective electronic and ionic conductivities, exchange current density, operating temperature, output current density, electrode- and electrolyte-particle radii, composition and porosity of the cathode inter-layer. The comprehensive study shows conclusively that a cathode inter-layer thickness in a range of 10-20 μm is optimal for all practical material choices and microstructure designs.     

Mathematical Modeling of Drying Processes Using Methods of the Nonequilibrium Thermodynamics and Percolation Theory

A twofold refinement of the basic mathematical model for describing a coupled heat and mass transfer taking place in porous media is presented. The common application of irreversible thermodynamics and fluctuation theory of phase transitions is proposed for calculating the moisture level and temperature. Instead of parabolic partial differential equations, hyperbolic type partial differential equations are used. The relaxation time constants, whose percolation state-dependence is also taken into account, are incorporated into this formalism. Some possible new research domains in mathematical and statistical physics are also indicated.     

Electronic Current Distribution Calculation for a Ni‐YSZ Solid Oxide Fuel Cell Anode

A simulation of a nickel‐yttrium stabilized zirconium oxide (Ni‐YSZ) solid oxide fuel cell cermet anode was used to determine the electronic current distribution within the percolating networks of nickel particles distributed in the electrode. The anode is simulated via a Monte–Carlo percolation model and current distribution is calculated via a relaxation algorithm. Nickel particle current densities are reported as a ratio to the total anode current density allowing results to be applied to any anode current density. Calculated current distributions were drastically affected by the volume percent of nickel as well as anode porosity. Experiments were performed to determine failure current densities of thin nickel wires to establish the relationship between critical current densities and surface area or volume of the wires. Both reducing and oxidizing environments were used for these measurements over a temperature range up to 800 °C.     

An electrically conducting polymer/graphene composite with a very low percolation threshold

A graphene nanosheet/ultra-high molecular weight polyethylene composite with a segregated structure has been fabricated using water/ethanol solvent-assisted dispersion and hot compression at 200 °C. A percolation threshold as low as 0.070 vol.% has been achieved because of the formation of a two-dimensional conductive network.     

自燃煤层逾渗漏风裂隙的分形特征研究

探讨了煤层巷道巷旁煤柱及采空区冒落浮煤逾渗漏风裂隙的分形特征,并对东滩煤矿某工作面煤层巷道构造位置逾渗漏风裂隙的形成与扩展情况进行了分析和讨论。     

应用逾渗理论计算非稳态法油水相渗曲线

测定油水相对渗透率曲线的方法有稳态法和非稳态法,由于后者能好地模拟油藏开发动态,而且测定简单,需时较短,所以实验室一般采用该法,但是非稳态法计算较复杂,而且用各种方法计算出的相对渗透率曲线能否真正反映实际情况,至今仍有争议,油于有些实验不能满足JBN法的许多限制条件,计算出的相渗曲线形状极不规则,所以提出了历史拟合法,自动历史拟合法一般行假定相对渗透率与饱和度符合某函数关系,再通过拟合各时廖的累积产油量或压差来求解函数式中的有关参数,因此,显然该法总能量出光滑的相渗曲线,但储集层岩石（尤其是非质岩石）的实际相渗曲线并一不定光滑,还存在润湿性也不均匀的情况,不仅用某个单一的函数关系来描述过于简单,而且拟合出的参数物理背景不明确,此外,在方程的求解过程中若要考虑毛管压力,一般也是近似地使用某函数,而该函数式往往由其它岩样的毛管压力测试资料求出,不一定能代表所研究的岩样。