High-Precision Flow Numerical Simulation and Productivity Evaluation of Shale Oil Considering Stress Sensitivity

Continental shale oil reservoirs,characterized by numerous bedding planes and micro-nano scale pores,feature significantly higher stress sensitivity compared to other types of reservoirs.However,research on suitable stress sensitivity characterization models is still limited.In this study,three commonly used stress sensitivity models for shale oil reservoirs were considered,and experiments on representative core samples were conducted.By fitting and comparing the data,the“exponential model”was identified as a characterization model that accurately represents stress sensitivity in continental shale oil reservoirs.To validate the accuracy of the model,a two-phase seepage mathematical model for shale oil reservoirs coupled with the exponential model was introduced.The model was discretely solved using the finite volume method,and its accuracy was verified through the commercial simulator CMG.The study evaluated the productivity of a typical horizontal well under different engineering,geological,and fracture conditions.The results indicate that considering stress sensitivity leads to a 13.57%reduction in production for the same matrix permeability.Additionally,as the fracture half-length and the number of fractures increase,and the bottomhole flowing pressure decreases,the reservoir stress sensitivity becomes higher.

Simulation Method and Feature Analysis of Shutdown Pressure Evolution During Multi-Cluster Fracturing Stimulation

Multistage multi-cluster hydraulic fracturing has enabled the economic exploitation of shale reservoirs,but the interpretation of hydraulic fracture parameters is challenging.The pressure signals after pump shutdown are influenced by hydraulic fractures,which can reflect the geometric features of hydraulic fracture.The shutdown pressure can be used to interpret the hydraulic fracture parameters in a real-time and cost-effective manner.In this paper,a mathematical model for shutdown pressure evolution is developed considering the effects of wellbore friction,perforation friction and fluid loss in fractures.An efficient numerical simulation method is established by using the method of characteristics.Based on this method,the impacts of fracture half-length,fracture height,opened cluster and perforation number,and filtration coefficient on the evolution of shutdown pressure are analyzed.The results indicate that a larger fracture half-length may hasten the decay of shutdown pressure,while a larger fracture height can slow down the decay of shutdown pressure.A smaller number of opened clusters and perforations can significantly increase the perforation friction and decrease the overall level of shutdown pressure.A larger filtration coefficient may accelerate the fluid filtration in the fracture and hasten the drop of the shutdown pressure.The simulation method of shutdown pressure,as well as the analysis results,has important implications for the interpretation of hydraulic fracture parameters.

Three-Dimensional Finite Element Numerical Simulation and Physical Experiment for Magnetism-Stress Detecting in Oil Casing

The casing damage has been a big problem in oilfield production. The current detection methods mostly are used after casing damage, which is not very effective. With the rapid development of China's offshore oil industry, the number of offshore oil wells is becoming larger and larger. Because the cost of offshore oil well is very high, the casing damage will cause huge economic losses. What's more, it can also bring serious pollution to marine environment. So the effective methods of detecting casing damage are required badly. The accumulation of stress is the main reason for the casing damage. Magnetic anisotropy technique based on counter magnetostriction effect can detect the stress of casing in real time and help us to find out the hidden dangers in time. It is essential for us to prevent the casing damage from occurring. However, such technique is still in the development stage. Previous studies mostly got the relationship between stress and magnetic signals by physical experiment, and the study of physical mechanism in relative magnetic permeability connecting the stress and magnetic signals is rarely reported. The present paper uses the ANSYS to do the three-dimensional finite element numerical simulation to study how the relative magnetic permeability works for the oil casing model. We find that the quantitative relationship between the stress' s variation and magnetic induction intensity's variation is: Δδ =K* ΔB, K = 8.04×109, which is proved correct by physical experiment.

Numerical Study and Economy Analysis of Two Heated Crude Oil Pipelines Laid in One Ditch

In this paper,the transportation economy of two heated crude oil pipelines laid in one ditch is analyzed by taking into account the influence of operating temperature,interval between two pipelines,and distance between two heating stations on the heating energy consumption.To analyze the transportation economy,the two heated crude oil pipelines laid in one ditch are simulated under four operating conditions based on an unstructured finite volume method.Compared with laying two crude oil pipelines separately in two ditches,the results attest notably higher soil temperature,meaning reduced heat dissipation of each pipeline by laying two pipelines in one ditch.It is inferred that for the same desired oil temperature at the inlet of the next heating station,laying two pipelines in one ditch requires lower oil temperature at the outlet of heating station,indicating decreased energy cost at the heating station and improved transportation economy.Then economy analysis of four configurations of laying two pipelines in one ditch is performed.By comparing the results of four conditions,the interval between two pipelines of 1.2 m is found to save the energy most efficiently,which is as large as 26.6%compared with that of laying two pipelines in two separate ditches.In addition,narrowing the pipeline interval and extending the distance between heating stations is beneficial to save heating energy.This study is expected to provide valuable guidance for operation optimization of heated crude oil pipelines.

Simulation Study of the Workspace of the Parallel Machine Tool

A new three dimensional simulation method is introduced to study the workspace of a 6 PSS (P denotes a prismatic kinematic pair, S denotes a spherical kinematic pair) parallel machine tool. This algorithm adopts the method of numerical analysis to investigate the boundary points in a series of sections which form the surface of the workspace. That is, to study such points that have the largest polar radius on a certain section in a system of polar coordinates according to conditions of constraint. The constraint conditions considered in the article include the maximum and minimum displacements of each dieblock, the maximum and minimum angles of oscillation in each hinge. By converting the constraint inequalities into constraint equations, the largest polar radius corresponding to every constraint condition can be evaluated and the minimum one is used to decide the boundary point. This algorithm greatly simplifies the computational process and can be used to analyze any section of the workspace. It provides a theoretical basis for the structural design of such a machine tool.

3D Finite Element Simulation of Tunnel Boring Machine Construction Processes in Deep Water Conveyance Tunnel

Applying stiffness migration method,a 3D finite element mechanical model is established to simulate the excavation and advance processes.By using 3D nonlinear finite element method,the tunnel boring machine(TBM) excavation process is dynamically simulated to analyze the stress and strain field status of surrounding rock and segment.The maximum tensile stress of segment ring caused by tunnel construction mainly lies in arch bottom and presents zonal distribution.The stress increases slightly and limitedly in the course of excavation.The maximum and minimum displacements of segment,manifesting as zonal distribution,distribute in arch bottom and vault respectively.The displacements slightly increase with the advance of TBM and gradually tend to stability.

Analysis of the Pump-turbine S Characteristics Using the Detached Eddy Simulation Method

Current research on pump-turbine units is focused on the unstable operation at off-design conditions, with the characteristic curves in generating mode being S-shaped. Unlike in the traditional water turbines, pump-turbine operation along the S-shaped curve can lead to difficulties during load rejection with unusual increases in the water pressure, which leads to machine vibrations. This paper describes both model tests and numerical simulations. A reduced scale model of a low specific speed pump-turbine was used for the performance tests, with comparisons to computational fluid dynamics（CFD） results. Predictions using the detached eddy simulation（DES） turbulence model, which is a combined Reynolds averaged Naviers-Stokes（RANS） and large eddy simulation（LES） model, are compared with the two-equation turbulence mode results. The external characteristics as well as the internal flow are for various guide vane openings to understand the unsteady flow along the so called S characteristics of a pump-turbine. Comparison of the experimental data with the CFD results for various conditions and times shows that DES model gives better agreement with experimental data than the two-equation turbulence model. For low flow conditions, the centrifugal forces and the large incident angle create large vortices between the guide vanes and the runner inlet in the runner passage, which is the main factor leading to the S-shaped characteristics. The turbulence model used here gives more accurate simulations of the internal flow characteristics of the pump-turbine and a more detailed force analysis which shows the mechanisms controlling of the S characteristics.

A New Method to Determine the Grid Directions in Reservoir Numerical Simulation

Grid direction selection and grid size design are two important elements that need to be considered in the grid direction design in reservoir numerical simulation. Reservoir engineers normally utilize geological data (such as the distribution of fractures, low permeability zones, faults and major stress) and simulation experiences to design the grid direction of simulation model qualitatively. The research of the paper indicates that the key to determine the grid direction is to determine the principal permeability direction. Under the circumstances of few static materials, a new grid direction determination method has been developed by using field data (well location map and inter-well permeability) on the bases of Darcy’s law and tensor analysis theory. The grid direction of WZ11-7 Oilfield simulation model has been determined using four production wells and two production zones (L1 and L3) in WZ11-7-2 well group, the results are in conformity with the geological studied major stress. Therefore, this method can give insights into the numerical simulation study.

Methods in Oil Recovery Processes and Reservoir Simulation

The exploitation of an oil field is a complex and multidisciplinary task, which demands a lot of prior knowledge, time, and money. A good reservoir characterization is deemed essential in the accomplishment of Enhanced Oil Recovery (EOR) processes in order to estimate accurately the properties of the porous medium affecting the flow properties. Several techniques at a field scale are currently being used to determine these properties, which are time and money consuming. But these alone do not guarantee the success of the project. Reservoir simulation and numerical techniques were then included in the pre-development and follow-up studies as an effective tool to determine the productivity and future behavior of the oil field. As the computational power increased, more advanced and detailed models were developed, including different chemical and physical phenomena. But alongside this process, there was an active research in the area of reservoir simulation, improving the accuracy and efficiency of the numerical schemes used for the flow, transport, and energy equations. The aim of this review is to address the topics described. Firstly, the origin of an oil recovery process, the economic factors and field tests involved are introduced. Secondly, the oil and porous medium origin and characterization as well as an introduction to the fundamental concepts and equations are associated to reservoir simulation. Finally, a brief description and analysis of the techniques are used in reservoir simulation employing finite difference methods, their downsides and possible ways to overcome these problems.

基于高维混合模型的离心泵叶轮子午面优化设计

为提高离心泵在设计工况下的运行效率和扬程,提出一种基于高维混合模型的离心泵叶轮优化设计方法.选取一台比转数为157的单级离心泵作为研究对象,通过CFturbo软件对优化变量进行参数化,然后结合数值模拟获得高维混合模型的训练集.在此基础上采用获取的训练集通过MATLAB机器学习得出效率、扬程与优化参数之间关于支持向量回归的高维模型,并采用遗传算法寻优.在设计工况下,所拟合的高维混合模型预测的效率和扬程值比原模型分别高1.5%和3.2 m,数值模拟验证优化方案的效率和扬程分别比原模型高0.9%和2.1 m.算例研究表明,将高维混合模型应用于离心泵叶轮的优化设计中可以实现快速寻优并提高离心泵水力性能.

动态热条件下原油罐储维温过程主要影响因素分析

掌握原油罐储维温过程主要影响因素,对原油库实现节能降耗目的起重要作用。在建立动态热条件下含蜡原油罐储维温过程三维理论模型的基础上,提出了加热盘管空间结构、周向效应对罐内对流传热的影响,划分了内、外因素影响区以及过渡区域;采用多元非线性回归的方法,建立不同季节边界位置主控影响因素模型,定量表征了罐边界油温与内、外因素之间的作用机制。结果表明:罐内大涡结构受无加热盘管区域局部湍涡影响,导致大涡结构向无盘管区域发生偏移。罐底低温区域受盘管周向效应影响较大,罐顶边界油品受内外因素影响大,形成最大厚度1.79 m的外界环境影响区;罐壁受保温层影响,只形成了内部维温热流影响区;冬季罐底形成了0.13 m的外界土壤影响区。

航空发动机用滑油泵组碟簧压紧有限元分析

为保证滑油泵组关键部件配流盘与偏心泵体的稳定压紧及泵盖的安全性,依据GB/T 1972—2005标准,选用2只单片碟簧以精准对合方式安装于滑油泵组上.在考虑潜在温度场热变形的影响下,采用热固耦合方法,基于Workbench平台对滑油泵组在不同碟簧初始压缩量(0.6,0.7,0.8,0.9 mm)下进行有限元分析.研究结果表明:当初始压缩量小于0.7 mm时,滑油泵的主要部件受到的压紧力较小,主要受油液周向推力的影响;随着初始压缩量从0.7 mm增至0.9 mm,预压缩端的变形量呈现相应的增长趋势,同时滑油泵体挡板所承受的轴向力也随着初始压缩量的递增而呈现线性增长的规律;在此过程中,配流盘与偏心泵体所受到的轴向推力随着初始压缩量的增大而逐渐增大,确保其能够有效地被压紧且泵盖保持完好无损.研究结果不仅为滑油泵组的初始安装提供了理论依据,而且有助于指导实际工程应用中的安装操作,从而确保滑油泵组的正常运行与使用寿命.

新型液阻式泵阀冲击特性研究

为了降低阀芯与阀座冲击应力减小二者间冲击磨损,提出一种液阻式新型泵阀。采用数值仿真方法对泵阀液阻结构参数进行了优化,并仿真计算了阀芯与阀座的冲击速度和泵阀碰撞冲击的压力接触情况。对比分析了液阻泵阀和传统泵阀的运动特征及冲击应力结果,并搭建试验台架对仿真模型结果进行验证。结果表明,在阀芯下落阶段,带液阻结构的泵阀的回落速度明显小于传统泵阀,传统泵阀阀芯与阀座相接触的速度达到了0.118 m/s,而带液阻结构泵阀的阀芯与阀座相接触的速度仅为传统泵阀的1/6左右,约为0.02 m/s;带液阻结构的泵阀只发生了1次碰撞,而传统泵阀发生了2次碰撞,在碰撞时,带液阻结构的泵阀阀芯与阀座上的最大接触应力约为260 MPa,而传统泵阀第1次碰撞为190 MPa,第2次为270 MPa;液阻式泵阀能明显降低阀芯与阀座相接触的速度,降低冲击应力,从而减小泵阀的冲击磨损。研究结果可为液阻式泵阀的设计和应用提供参考。

用于电梯曳引机减振的MR-SRC减振器设计与分析

针对现有曳引机减振常采用的高分子减振垫因环境因素而引发性能大幅退化问题,以电梯曳引机减振器的工程应用需求为导向,确定减振器所需阻尼元件的刚度后,采用真空渗流技术将硅橡胶填充入金属橡胶孔隙并形成包覆,研制出一款耐环境影响的高性能金属橡胶/硅橡胶连续互穿相复合减振材料(metal rubber-silicone rubber continuous interwoven phase composite damping material, MR-SRC)。然后基于实际结构建立电梯曳引机的有限元数值模型。对加装MR-SRC减振器前后的电梯曳引机进行了模态分析,确定了整体结构的固有频率和振型。对MR-SRC减振器进行冲击响应分析,对比不同MR-SRC材料和冲击载荷对响应的影响,校核减振器的强度。接着,基于MR-SRC的近似等效,对减振器系统的冲击响应进行了理论计算,得出金属橡胶密度为1.8 g/cm^(3)的MR-SRC减振器对减振效果最佳。最后将所制备的MR-SRC减振器安装于实际电梯曳引机,按照电梯减振国标要求,测试电梯在运行过程中的加速度和速度变化,计算并校核电梯运行的相关特性参数。该文章提出的减振器为电梯安全可靠运行提供了一种新途径。

机械加工中有限元技术的计算精度优化研究

有限元模型技术被广泛应用于机械加工领域,其也是实现数字控制与现代加工的核心理论技术,得到了各领域研究者的广泛关注与深入探讨。基于有限元模型的计算仿真模拟技术能够大幅提升机械加工制造的精度,大量的机械加工零件实验也为有限元模型提供详细的数据参考。文中通过总结有限元分析技术的研究历史,分析归纳了当前有限元分析技术中精度优化的核心策略及其不足之处,展望了在机械加工过程中有限元分析技术的未来发展方向。

黏温黏压下径向柱塞泵滑靴副温度分布与泄漏量分析

针对高压大排量径向柱塞泵滑靴副摩擦失效和泄漏问题,以XDP1000型径向柱塞泵为例,对滑靴副温度分布与泄漏量进行了流场仿真和数值计算。首先,根据滑靴柱塞组件运动学特性分析,求解了滑靴偏转角变化规律,并通过建立滑靴副不同通道流量计算公式的方式,建立了滑靴副静压支承特性方程;然后,建立了滑靴副泄漏功率损失和摩擦功率损失模型,求解了滑靴副最佳油膜厚度,并分析了最佳油膜厚度的变化规律;最后,在考虑了油液黏温黏压特性的基础上,通过流场数值计算的方式,研究了滑靴副温度分布与泄漏量随径向柱塞泵工况参数的变化规律。研究结果表明:额定工况下,滑靴副最佳油膜厚度值约为14μm,滑靴副最佳油膜厚度值随着转子转角的增大而增大,随着工作压力和温度的增大而减小;滑靴运动方向侧油膜温度较另一侧高13 K,滑靴副温度值基本不受工作压力的影响,而随着转速的增大而升高;滑靴副阻尼孔泄漏量较滑靴边界泄漏量大0.02 kg/s,而且泄漏量随着压力、转速和油液温度的增大而增大。该研究结论可为高压大排量径向柱塞泵滑靴副设计及优化提供参考。

水泵水轮机导水机构与转轮动应力特性分析

为探究水泵水轮机转轮和导水机构的动应力特性,通过建立水泵水轮机导水机构(固定导叶与活动导叶)及转轮的固体域模型,并基于流固耦合的方法对转轮、导水机构在水泵水轮机发电、抽水等多工况展开计算分析,以获得转轮及导水机构的应力特性。计算结果表明:转轮叶片与上冠“T”型连接处的应力集中与转轮进口处旋涡发展状态有关;转轮与活动导叶间的动静干涉是无叶区压力脉动的主要来源,且主频为叶片通过频率;较小开度或低水头工况下机组运行靠近不稳定区,活动导叶与转轮的动应力均较大,但活动导叶对水流的约束引导作用使其动应力值相比于转轮更高,且流量的增大有利于降低转轮所受动应力。因此可考虑通过改变导叶尾端与转轮进口间距,调整无叶区宽度或调整机组运行区域,避免长时间运行在低负荷、小开度工况下可进一步改善转轮所受动应力情况。

抽水蓄能机组水轮机工况启动过程内部流场分析

本文采用CFD数值模拟的方法,模拟计算了抽水蓄能机组在水轮机工况启动过程内部流场特征。得到了在活动导叶开启过程中的速度、压力随时间的瞬态分布规律,讨论了蓄能机组开启过程中外特性的变化曲线。结果表明:活动导叶的开启规律可以大体分为五个阶段。活动导叶的开启规律是先缓慢开启,然后以较快的速度关闭,最后再保持到空载的开度,从第四阶段,导叶再逐渐打开直到额定开度。转轮扭矩和机组流量呈现出先增大后减小的趋势,当导叶逐渐打开时,转轮扭矩和机组流量再逐渐上升。本文为研究蓄能机组水轮机工况下启动过程的内部流动变化提供了参考依据,同时对提高水轮机工况的启动稳定性具有重要意义。

基于支撑力平衡的柱塞泵滑靴副油膜厚度动态求解方法

通过改进轴向柱塞泵的滑靴副与柱塞的结构设计以稳定建立滑靴油膜,这是轴向柱塞泵当前的研究热点之一。柱塞泵滑靴副油膜厚度的动态特性对分析柱塞泵滑靴副的支撑特性至关重要,为此,提出了一种基于支撑力平衡的柱塞泵滑靴副油膜厚度动态求解新方法。首先,对滑靴副的受力平衡机理进行了分析,并构建了柱塞泵运动学和动力学模型;然后,构建了柱塞泵整泵流场仿真模型,求解了包含滑靴底部支撑力、柱塞腔压力等在内的滑靴副支撑动态边界,并采用容积效率试验数据验证了整泵流场仿真的准确性;最后,建立了滑靴副油膜承载模型,分析了滑靴副油膜支撑特性,提出了基于插值计算理论的柱塞泵滑靴副油膜承载尺度动态求解方法,对1600 r/min与600 r/min两种典型工况的滑靴副油膜动态进行了计算。研究结果显示:大排量柱塞泵转速为1600 r/min时,柱塞惯性力导致高压侧油膜厚度进一步减薄,高压转低压过程中,柱塞腔内出现压力骤降,使滑靴副油膜无法形成,导致滑靴与斜盘发生刚性接触,在该区域内发生异常磨损;而在低转速工况(600 r/min)时,滑靴底面能够有效形成油膜,保证柱塞泵低速运行的可靠性。这表明基于支撑力平衡的柱塞泵滑靴副油膜厚度动态求解方法可以快速地对不同工况下的柱塞泵滑靴副油膜厚度进行求解。

汽车机油泵体压铸工艺数值模拟与优化

为满足汽车铝合金机油泵体压铸件高气密性和高强度的要求,解决该铸件缩松、缩孔缺陷问题,进行压铸工艺设计和优化。首先对铸件进行工艺分析,根据经验分别设计浇注排溢系统并初步选取工艺参数;再运用田口正交试验法设计了5因素4水平压铸工艺参数方案,并使用Procast进行数值模拟。将16组正交试验结果基于信噪比进行极差和方差分析,结果表明,模具温度对缩松缩孔的影响最为显著,5因素的最优工艺参数为:浇注温度650℃、模具温度240℃、慢/快压射距离200 mm/60 mm、快压射速度为3.0 m/s、慢压射速度为0.2 m/s。数值模拟结果显示,该工艺参数组合下铸件缩松、缩孔体积为1.067 cm^(3),较优化前降低了26.5%。试模结果表明,铸件外观完好,关键部位X射线探伤显示无明显缩孔;采用金相显微镜(OM)和扫描电镜(SEM)对铸件进行组织观察,发现铸件各区域组织致密;力学性能测试表明,压铸件显微硬度大于HV85,同等工艺下试棒平均拉伸强度为253.36 MPa,铸件满足使用要求。