Fluid flow properties for different classes of intermediate wettability as studied by network modelling

Most clastic reservoirs display an intermediate type of wettability. Intermediate wettability covers several local wetting configurations like fractional wet and mixed-wet where the oil-wet sites could either be in the large or smaller pores. Clastic reservoirs show a large variation in fluid flow properties. A classical invasion–percolation network simulator is used to investigate properties of different intermediate wet situations. Variation in wetting properties like contact angles, process dependent contact angles, contact angle distribution, and fraction of oil wet sites are investigated. The fluid flow properties analysed in particular are residual oil saturation and normalized endpoint relative permeability. Results from network modelling have been compared to reservoir core analysis data. The network models applied are at the capillary limit, while the core flood results are clearly viscous influenced. Even though network modelling does not cover all the physics involved in fluid displacement processes, results show that data from simulations are sufficient to present trends in fluid flow properties which are comparable to experimental data.     

Flow behaviour in the presence of wettability heterogeneities

The physical processes occurring during fluid flow and displacement within porous media having wettability heterogeneities have been investigated in specially designed heterogeneous visual models. The models were packed with glass beads, areas of which were treated with a water repellent to create wettability variations. Immiscible displacement experiments show visually the effect of wettability heterogeneities on the formation of residual oil and recovery due to capillary trapping. This work demonstrates by experiment the importance of incorporating reservoir heterogeneity into pore displacement analysis, essential for the correct interpretation of core data and for directing the route for scale-up of the processes to reservoir scale.     

Simulation of capillary pressure curves using bond correlated site percolation on a simple cubic network

A stochastic approach to network modelling has been used to simulate quasi-static immiscible displacement in porous media. Both number-based and volume-based network saturation results were obtained. Number-based results include: number-based saturation curves for primary drainage, secondary imbibition and secondary drainage, fluid distribution data, and cluster trapping history. Using pore structure data of porous media, it is possible to convert the number-based curves to capillary pressure — saturation relationships. Pore size distribution functions and pore shapes which are thought to closely represent Berea sandstone samples were used to predict the capillary curves. The physical basis of these calculations is a one-to-one correspondence between the cumulative node and bond index fractions in the network analysis, and the cumulative number-based distributions of pore body and pore throat diameters, respectively. The oil-water capillary pressure curve simulated for primary drainage closely resembles those measured experimentally. The agreement between the simulated and the measured secondary imbition and secondary drainage curves is less satisfactory.     

Experimental study of two-phase flow in three sandstones. II. Capillary pressure curve measurement and relative permeability pore space capillary models

By means of the porous plate method and mercury porosimetry intrusion tests, capillary pressure curves of three different sandstones were measured. The testing results have been exploited jointly with three relative permeability models of the pore space capillary type (Burdine’s model type), these models are widely used and in rather distinct fields. To do so, capillary pressure has been correlated to saturation degree using six of the most popular relations encountered in the literature. Model predictions were systematically compared to the experimentally measured relative permeabilities presented in the first part of this work. Comparison indicated that the studied models underestimate the water relative permeability and over-estimate that of the non-wetting phase. Moreover, this modeling proves to be unable to locate the significant points that are the limits of fields of saturation where the variation of the relative permeabilities becomes consequent. We also showed that, if pore structure is modeled as a “bundle of capillary tubes”, model predications are independent of the capillary pressure curve measuring method.     

离心模型试验边界效应分析

通过对模型土进行加卸载的离心模型试验，分析边界摩擦力对土体变形的影响。由试验可以得到土层表面的弹性变形曲线，根据模型土体的位移边界条件，假设土层的位移函数，运用最小势能原理，求出边界磨擦力的大小，以及离心机加载过程中，在惯性力场和边界摩擦力作用下，模型土体的位移计算公式。通过试验和计算认为，在离心模型试验中，边界摩擦力对粘性土体的位移场有很大影响，应采取一定的措施减小摩擦力。     

An Integral Method to Calculate Water Saturation in a Centrifuge Experiment to Determine Capillary Pressure

The centrifuge method is commonly used to determine the capillary pressure of a porous medium, and the original approximating method for data analysis developed by Hassler and Brunner is still being used. Its limitations are, however, not well understood. Application to analyze experiments where one of the assumptions was obviously violated had been given in the literature. While the result appeared to be quite reasonable, it was not clear how close was it to reality. One of the objectives of this paper is to review the assumptions that is required to develop this method, so that the experimental condition in which it is applicable can be established. The other objective is to derive a completely different solution technique to this problem. There is no need to assume that the ratio of the inlet radius to the exit radius of the core to the center of the centrifuge be close to 1. With the freedom from this limitation it is, therefore, possible to construct machines at lower cost and to improve on the data quality by allowing longer cores.     

Discussion of Techien Chen, 1997, ‘An Integral Method to Calculate Water Saturation in a Centrifuge Experiment to Determine Capillary Pressure’

That discussion recognizes that the above paper deals with one of the main problems for reserves and reservoir evaluation, i.e. the determination of capillary pressure curves using the centrifuge technique. However, it is explained that the subject was not properly addressed and that sections of the paper are out of date, confusing or eventually wrong. For a more relevant overview on the subject, it is recommended to refer to the corresponding survey by the Society of Core Analysts.     

Effect of capillary pressure on the approach to residual saturation

The approach to residual oil saturation during the immiscible displacement of oil as predicted by the multiphase Darcy equations is studied. It is well known that when the capillary pressure term is neglected, one arrives at the Buckley-Leverett formulation according to which the inlet face attains residual oil saturation instantaneously. This result may, however, be strongly influenced by the inclusion of the capillary pressure term. In this paper it is shown that when the relative permeability and capillary pressure functions have power law dependencies on the saturation deviation from residual oil condition, the long time solution exhibits a power law decay toward residual saturation. Moreover, the power law decay solution is found to be unique and independent of the initial condition. The relationship of this solution to the classical Buckley-Leverett result is shown. Finally, generalization to the time varying flow rate case is addressed. As a verification of the theoretical conjectures, the power law solution is compared with direct numerical simulation of the two phase flow equations.     

双向载荷作用下试件应力分布的理论和实验分析

本文利用弹性理论对十字形试验板的应力分布进行了推导，并得出一个近似计算公式，结合电测实验进行校核，为直观起见，用有限元画出了该模型的应力等值线，证明该计算公式基本正确     

随机疲劳试验前Instron2165电液疲劳试验系统的分析

本文介绍了随机疲劳试验之前我们对Ｉｎｓｔｒｏｎ计算机控制２１６５电液疲劳试验系统做的分析方法与过程．     

天然气水合物分解对地层稳定性影响的离心机实验模拟

水合物分解后将引起地层强度的降低,可能造成海床沉陷、滑塌以及海洋结构物基础的破坏。针对该问题,首先以南海浅层粉砂为沉积物骨架,采用生物厌氧发酵技术合成水合物沉积物,然后进行水合物热分解引起地层响应的离心机实验模拟,获得了水合物分解引起地层变形与滑塌的特征以及孔隙压力发展的物理过程,为研究水合物分解引起海床失稳的条件进行了新的尝试。     

Identification of the four orthotropic plate stiffnesses using a single open-hole tensile test

The identification of mechanical parameters for real structures is still a challenge. With the improvement of optical full-field measurement techniques, it has become easier, but in spite of many publications showing the feasibility of such methods, experimental results are still scarce. In this paper we present a first step towards a global approach of mechanical identification for composite materials. The chosen mechanical test is an open-hole tensile test according to standard recommendations. For the moment, experimental data are provided by a moiré interferometry setup. The global principle of the identification developed in this paper is to minimize a discrepancy between experimental and theoretical results, expressed as a cost function, using a Levenberg-Marquardt algorithm. This approach has the advantage of having high adaptability, largely because the optical system, the signal processing as well as the mechanical aspects, can be taken into consideration by the model. In this paper we consider different types of cost functions, which are tested using an identifiability criterion. Although mechanically based cost functions have been studied, a simpler mathematical form is finally more efficient. Two different models were tested. The first is an analytical model based on the Lekhnitskii approach. This approach has the advantage of being a meshless solution; however, the results appeared to be partially false due to boundary effects, leading to a second approach, a classical finite element analysis. The resulting identified values are similar to values from classical mechanical tests (within 6%). which, in practice, validates our approach.     

改进的容重增加法原理及离心模型试验数值模拟

容重增加法作为一种边坡稳定分析方法本身具有一定的缺陷,计算结果常常偏差较大,甚至可能无法得出结果。针对容重增加法的缺陷,定量分析了容重增加法的误差来源,并通过公式推导对改进容重增加法的原理进行了分析。针对改进的容重增加法,设计了不同参数的边坡模型,将容重增加法、强度折减法与改进的容重增加法进行对比分析,研究改进方法的改进效果。然后,利用ACADS边坡稳定分析例题,验证了改进方法在非均质边坡中的应用效果。最后,将改进前后的容重增加法运用到土工离心模型试验的结果分析中,并将试验结果与模拟结果进行对比分析,验证了用改进的容重增加法分析离心模型试验结果的可行性。本文的研究为容重增加法改进方法的应用提供了理论依据,并为土工离心模型试验的相关分析提供了参考。     

某发动机热试车的振动环境预示方法研究

发动机热试车试验在新型运载器的研制过程中起到重要作用,可用于预测运载器在飞行中的振动环境.由于载荷不等效,试验数据量有限,使得难以直接通过试验数据建立同一结构在不同系统下的映射关系模型.本文提出了一种基于试验数据的振动环境预示方法,以某发动机两次热试车试验数据为对象,分别提取了反映结构特性的动力学模型,基于载荷等效原则...     

离心机上辨识陀螺加速度计二次项系数的优化试验设计

提出了一种在带有反转平台的精密离心机上标定陀螺加速度计误差模型二次项系数K 2的D-最优试验方案。应用该D-最优试验方案,通过重复试验,能够在测试点最少的情况下获得高测试精度,实现陀螺加速度计误差模型系数的最优(D-最优的)辨识。推导了测量随机误差、试验方案的测试点、测试点的重复测试次数以及误差模型系数方差之间的关系式。精度分析的结果表明,应用D-最优试验方案,采取重复试验的方法,能够有效地减小二次项系数K的估计量的方差,从而提高K的辨识精度。     

陀螺仪漂移测试小角度伺服法实验方案的改进

为了提高陀螺仪的使用精度,研究了陀螺仪漂移测试的伺服法实验技术.依托973项目,在国内首次完成了高精度单自由度静压液浮陀螺仪的伺服法实验.找到了影响小角度伺服法实验测试精度的主要误差源,即小角度伺服法实验的方法误差,通过对该误差的分析,提出了改进的小角度伺服实验方案.建立了小角度伺服法实验方法误差的仿真模型,用改进方案和原始方案分别进行了仿真和实验,结果表明改进方案同原始方案相比,陀螺仪漂移误差模型中的三项系数辨识精度均有提高.     

Experimental Study and Fractal Analysis of Heterogeneity in Naturally Fractured Rocks

Capillary pressure curves of six low porosity and low permeability core samples from The Geysers geothermal field were measured using the mercury-intrusion approach to characterize the heterogeneity of rock. One high permeability Berea sandstone core sample was analyzed similarly, for comparison. The maximum pressure of mercury intruded into the rock was about 200 MPa to reach the extremely small pores. Experimental data showed that the capillary pressure curves of The Geysers rock are very different from that of the Berea sandstone. It was found that the frequently used capillary pressure models could not be used to represent the data from The Geysers rock samples. This might be because of the fractures in the rock. To this end, a fractal technique was proposed to model the features of the capillary pressure curves and to characterize the difference in heterogeneity between The Geysers rock and Berea sandstone. The results demonstrated that the rock from The Geysers geothermal field was fractal over a scaling range of about five orders of magnitude. The values of the fractal dimension of all the core samples (six from The Geysers and one Berea sandstone) calculated using the proposed approach were in the range from 2 to 3. The results showed that The Geysers rock with a high density of fractures had a greater fractal dimension than Berea sandstone which is almost without fractures. This shows that The Geysers rock has greater heterogeneity, as expected.     

离心通风器结构分析

根据某发动机离心通风器6个故障件的破坏形貌测量分析结果及简化模型的光弹性试验和有限元计算结果，建立离心通风器壳体力学模型，并通过应力分析结果对结构进行疲劳分析、探讨失效原因．研究结果指出，由于壳体在油气混合环境中使用，其肋的转接台阶处具有高的应力集中、材料铸造表面粗糙；组织疏松等缺陷，肋的截面尺寸公差太大等多种因素造成零件的寿命降低，较多零件的失效．