A semi-analytical model for coupled flow in stress-sensitive multi-scale shale reservoirs with fractal characteristics

A large number of nanopores and complex fracture structures in shale reservoirs results in multi-scale flow of oil. With the development of shale oil reservoirs, the permeability of multi-scale media undergoes changes due to stress sensitivity, which plays a crucial role in controlling pressure propagation and oil flow. This paper proposes a multi-scale coupled flow mathematical model of matrix nanopores, induced fractures, and hydraulic fractures. In this model, the micro-scale effects of shale oil flow in fractal nanopores, fractal induced fracture network, and stress sensitivity of multi-scale media are considered. We solved the model iteratively using Pedrosa transform, semi-analytic Segmented Bessel function, Laplace transform. The results of this model exhibit good agreement with the numerical solution and field production data, confirming the high accuracy of the model. As well, the influence of stress sensitivity on permeability, pressure and production is analyzed. It is shown that the permeability and production decrease significantly when induced fractures are weakly supported. Closed induced fractures can inhibit interporosity flow in the stimulated reservoir volume (SRV). It has been shown in sensitivity analysis that hydraulic fractures are beneficial to early production, and induced fractures in SRV are beneficial to middle production. The model can characterize multi-scale flow characteristics of shale oil, providing theoretical guidance for rapid productivity evaluation.

Numerical modeling and parametric sensitivity analysis of heat transfer and two-phase oil and water flow characteristics in horizontal and inclined flowlines using OpenFOAM

Estimating the oil-water temperatures in flowlines is challenging especially in deepwater and ultra-deepwater offshore applications where issues of flow assurance and dramatic heat transfer are likely to occur due to the temperature difference between the fluids and the surroundings. Heat transfer analysis is very important for the prediction and prevention of deposits in oil and water flowlines, which could impede the flow and give rise to huge financial losses. Therefore, a 3D mathematical model of oil-water Newtonian flow under non-isothermal conditions is established to explore the complex mechanisms of the two-phase oil-water transportation and heat transfer in different flowline inclinations. In this work, a non-isothermal two-phase flow model is first modified and then implemented in the InterFoam solver by introducing the energy equation using OpenFOAM® code. The Low Reynolds Number (LRN) k-ε turbulence model is utilized to resolve the turbulence phenomena within the oil and water mixtures. The flow patterns and the local heat transfer coefficients (HTC) for two-phase oil-water flow at different flowlines inclinations (0°, +4°, +7°) are validated by the experimental literature results and the relative errors are also compared. Global sensitivity analysis is then conducted to determine the effect of the different parameters on the performance of the produced two-phase hydrocarbon systems for effective subsea fluid transportation. Thereafter, HTC and flow patterns for oil-water flows at downward inclinations of 4°, and 7° can be predicted by the models. The velocity distribution, pressure gradient, liquid holdup, and temperature variation at the flowline cross-sections are simulated and analyzed in detail. Consequently, the numerical model can be generally applied to compute the global properties of the fluid and other operating parameters that are beneficial in the management of two-phase oil-water transportation.

Pore-scale study of the pressure-sensitive effect of sandstone and its influence on multiphase flows

The pressure-sensitive effect on the pore structure of sandstone was investigated using X-ray computed micro-tomography and QEMSCAN quantitative mineral analysis. In a physical simulation study, we extracted the pore network model from digital cores at different confining pressures and evaluated the effect of pressure sensitivity on the multiphase displacement process. In both the pore network model and QEMSCAN scanning, the pore structure was observed to be damaged under a high confining pressure. Due to their different scales, the pores and throats exhibited inhomogeneous changes; further, the throats exhibited a significant variation compared to that exhibited by the pores. Meanwhile, the heterogeneity of the pore structure under the two aforementioned activities was aggravated by the elastic-plastic deformation of the pore structure.The pressure-sensitive effect increased the proportion of mineral particles, such as quartz(the main component of the core skeleton), and reduced the proportion of clay minerals. The clay minerals were originally attached to the pore walls or interspersed in the pores; however, as the pressure increased, the clay minerals accumulated in the pores resulting in blockage of the pores. While simulating the multiphase displacement process, increasing the confining pressure was observed to severely restrict the flowability of oil and water. This study promises to improve the efficiency of reservoir development in terms of oil and gas exploitation.

Introducing Fractal Dimension to Estimation of Soil Sensitivity to Preferential Flow

Food dye Brilliant Blue was introduced as the tracer in a dye-tracing experiment to obtain dye profile patterns of sandy loam soil, aeolian sandy soil, percolating paddy soil and permeable paddy soil. The dyed soil profiles were then photographed and the photos were scanned into a computer. Edited with certain software, only the dyed areas were left on the profile photos, which indicted the preferential flow paths for water and solute transport. Fractal dimensions of the dye patterns were calculated according to Arnold's function. Soil particle size distribution was analyzed by pipette method. The regression analysis showed that there was significant relationship between soil clay content and fractal dimension D of the dye pattern of soil profile. Based on the experiment results, the possibility of introducing fractal dimension to estimation of soil sensitivity to preferential flow is discussed.

Optimization of heat transfer in the thermal Marangoni convective flow of a hybrid nanomaterial with sensitivity analysis

The heat transfer rate of the thermal Marangoni convective flow of a hybrid nanomaterial is optimized by using the response surface methodology(RSM).The thermal phenomenon is modeled in the presence of a variable inclined magnetic field,thermal radiation,and an exponential heat source.Experimentally estimated values of the thermal conductivity and viscosity of the hybrid nanomaterial are utilized in the calculation.The governing intricate nonlinear problem is treated numerically,and a parametric analysis is carried out by using graphical visualizations.A finite difference-based numerical scheme is utilized in conjunction with the 4-stage Lobatto IIIa formula to solve the nonlinear governing problem.The interactive effects of the pertinent parameters on the heat transfer rate are presented by plotting the response surfaces and the contours obtained from the RSM.The mono and hybrid nanomaterial flow fields are compared.The hybrid nanomaterial possesses enhanced thermal fields for nanoparticle volume fractions less than 2%.The irregular heat source and the thermal radiation enhance the temperature profiles.The high level of the thermal radiation and the low levels of the exponential heat source and the angle of inclination(of the magnetic field)lead to the optimized heat transfer rate(Nux=7.46275).

Traffic flow sensitivity to visco-elasticity

This letter reports traffic flow sensitivity to visco-elasticity, with the traffic flow modeling briefly described at first and then used to do traffic flow simulations whose results can reflect the properties of spatial-temporal evolution of ring traffic flow. It reveals that visco-elasticity plays crucial role in formation of traffic flow patterns, implying that self-organization of traffic flow is crucial in determining traffic flow status.

SENSITIVITY COEFFICIENTS OF SINGLE-PHASE FLOW IN LOW-PERMEABILITY HETEROGENEOUS RESERVOIRS

Theoretical equations for computing sensitivity coefficients of wellbore pressures to estimate the reservoir parameters in low-permeability reservoirs conditioning to non-Darcy flow data at low velocity were obtained. It is shown by a lot of numerical calculations that the wellbore pressures are much more sensitive to permeability very near the well than to permeability a few gridblocks away from the well. When an initial pressure gradient existent sensitivity coefficients in the region are closer to the active well than to the observation well. Sensitivity coefficients of observation well at the line between the active well and the observation well are influenced greatly by the initial pressure gradient.

Analytical solution for Non-Darcian effect on transient confined-unconfined flow in a confined aquifer

This paper presents a new analytical solution to investigate the mechanism of transient confinedunconfined flow in a confined aquifer induced by pumping with a large rate during mine drainage.The study focuses on understanding the impact of non-Darcian effect on flow towards a fully penetrated pumping well.The nonlinear relationship between specific discharge and the hydraulic gradient is described using Izbash's equation.A novel approximate method is developed to linearize the mathematical model,and the solution is derived using the Boltzmann transform.The proposed solution is validated by comparing it with previous works.The findings indicate that increased non-Darcian index,quasi-hydraulic conductivity,and specific storage have negatively affect the development of the unconfined region and aquifer drawdown,as greater turbulence flow accelerates recharge to the pumping well.Drawdown is found to be sensitive to the non-Darcian index,quasi-hydraulic conductivity,while it is unaffected by specific yield and specific storage.The conclusions provide valuable insights for mine drainage and the application of geological and hydrological conditions.

鱼类产卵敏感期河流生态流速的分区分类阈值研究

敏感生态流量目标的合理制定是生态流量管理的重难点问题。针对目前敏感生态流量目标制定中存在的计算方法繁杂、关键参数缺乏等问题,本文以鱼类产卵期为重点,提出了分区分类河流敏感期生态流速和生态流量核算方法,制定了不同区域(东北、黄淮海、西南、长江中下游和东南沿海)、不同类型(按集水面积、山区河段和平原河段等划分)河流敏感期生态流速阈值。结果显示,全部分区分类推荐流速平均值为0.66 m/s,其中山区大站平均值为0.94 m/s、山区小站平均值为0.62 m/s、平原大站平均值为0.63 m/s、平原小站平均值为0.46 m/s。基于阈值核算了全国217个鱼类产卵生境保护河段的敏感期生态流量目标,并结合部分断面湿周法结果对阈值合理性与适应性进行了验证,验证结果表明相关阈值和方法适应于不同类型、不同规模河流,可为我国现阶段河流敏感生态流量管控提供参考。

FLOW-3D气泡流模型关键参数敏感性探究

为了探究FLOW-3D气泡流模型的黑匣子细节,以45°陡槽均匀流的试验数据为参考,对计算结果对临界韦伯数、临界毛细管数、初始气泡直径、拖曳阻力系数和Richardson-Zaki调节系数等模型参数的敏感性进行了探究。结果表明:明渠掺气水流中气泡尺寸主要受临界毛细管数控制,临界韦伯数仅在掺气水面附近对气泡大小有微弱影响。拖曳系数和Richardson-Zaki调节系数对结果的影响较大,而临界毛细管数、临界韦伯数以及气泡初始直径对计算结果的影响则相对较小。大于默认值的拖曳系数和Richardson-Zaki调节系数会提高湍流强度并增加掺气,但小于默认值的参数对计算结果的影响更为显著。因此,在使用FLOW-3D进行掺气水流模拟时,应主要对拖曳系数和Richardson-Zaki调节系数进行调校,以提高模型的准确性。

液阻全桥网络负载口独立电液系统节能控制策略仿真

针对传统电液控制系统节流损失大、能耗高、效率低的问题,采用液阻全桥网络搭建了具有负载口独立控制特性的新型电液控制系统,详细研究了该系统在典型四象限负载下的节能控制策略。液阻全桥网络电液系统由5个二位二通比例阀组成,根据其具有的负载口独立控制特性,将系统归纳为传统三位四通、负载口独立和负载敏感3种控制模式。传统三位四通下,两负载口开度控制模拟三位四通进出口耦合形式;负载口独立模式下,采用一腔控制流量另一腔阀口全开的控制策略;负载敏感模式下,控制泵出口压力比进油腔压力高一个定值,从而实现负载敏感功能。在超越负载下,3种模式都使用流量再生回路进行节能控制。AMESim+Matlab联合仿真结果表明,与传统的三位四通模式相比,三位四通流量再生、负载口独立、负载口独立流量再生、负载敏感模式分别节能43.38%、65.27%、77.91%、83.58%。

基于DEM-FEM耦合方法的碎屑流对桥墩最大冲击力的影响因素研究

碎屑流是我国山区最危险的地质灾害之一,山区桥墩常受到碎屑流冲击而开裂、倾斜甚至倒塌,给山区桥梁建设、运营带来严重的安全隐患。采用离散元方法(discrete element method,DEM)和有限元方法(finite element method,FEM)耦合的三维数值模拟方法模拟了碎屑流对双柱式桥墩的冲击效应,并结合斜槽试验,验证了耦合方法的准确性,进一步分析了碎屑流冲击坡度、距离和体积密度对桥墩冲击力的影响规律。结果表明,最大冲击力与碎屑流冲击坡度、距离和体积密度分别呈幂函数(指数大于1)、幂函数(指数小于1)和线性正相关。冲击坡度、距离和体积密度对最大冲击力的敏感度值分别为3.012、0.202、0.804,在桥梁碎屑流灾害防治时需重视冲击坡度和体积密度的影响。将冲击力的数值模拟值与流体动力学模型预测值对比分析表明,流体动力学模型理论公式能较好地预测桥墩所受的最大冲击力,最大预测误差低于23.6%。相关研究结果可为山区桥梁碎屑流灾害防治与设计提供一定的参考依据。

CCTA-AI联合FFR-CT诊断冠状动脉狭窄病变的应用价值研究

目的评估计算机断层扫描血管成像(CCTA)与人工智能(AI)联合心肌灌注分数(FFR-CT)对冠状动脉狭窄病变的诊断价值。方法选择于2022年1月至2023年2月到南阳市中心医院接受诊治的80例疑似冠状动脉狭窄病变患者作为观察对象。所有患者均接受CCTA以及冠状动脉造影(CAG)检查,其检查的间隔时间应在14天内,然后通过AI软件自动对CCTA的图像进行重建和计算,同时计算FFR-CT的数值。计算人工智能辅助的心脏计算机断层扫描(CCTA-AI)联合FFR-CT诊断的敏感度、特异度、准确度、阳性预测值和阴性预测值。结果80例患者经CAG检查确诊,72例患者为冠状动脉狭窄病变,占比为90%;8例患者为非冠状动脉狭窄病变,占比为10%。CCTA-AI联合FFR-CT检查的敏感度、特异度、阳性预测值、阴性预测值、准确度以及AUC值均高于CCTA-AI、FFR-CT单独检查,差异有统计学意义(P<0.05)。结论采用CCTA-AI联合FFR-CT检查诊断冠状动脉狭窄病变具有较高的诊断效能,其敏感度及特异度均得到显著提高。

离心压气机进口径向总压畸变不确定性分析

针对离心压气机实际运行过程中的进口畸变不确定性问题,提出了一种离心压气机进口径向总压畸变不确定性参数化表征模型。以跨声速Radiver离心压气机为研究对象,采用非嵌入式多项式混沌法和Sobol敏感性分析方法,研究了压气机气动性能受叶尖畸变、轮毂畸变两类进口径向总压畸变不确定性的影响,获得了对压气机气动性能影响最为显著的不确定性因素,并分析了不确定性因素影响压气机气动性能的相关流动机理。结果表明:相比于均匀来流,叶尖畸变、轮毂畸变均使压气机级多变效率下降近1.0%;轮毂畸变、叶尖畸变分别对级总压比、扩压器总压损失系数带来的影响较为显著,级多变效率受轮毂畸变影响下降1.4%,叶尖畸变使损失系数增大11.0%;相较于轮毂侧和叶尖侧畸变峰之间的相对位置,压气机气动性能对畸变峰的数值大小更敏感;受进口径向总压畸变影响下的压气机的性能恶化与扩压器叶片进口冲角不均匀分布导致的流动分离现象密切相关。研究工作表明了进口畸变不确定性在离心压气机不确定性分析中的重要性,对未来发展离心压气机鲁棒优化设计具有一定的学术意义和工程应用价值。

基于深度强化学习的TSN流排序和调度

针对现有研究寻找数据流最佳排序这一过程本身花费时间过多,没有工程可行的寻找最佳排序的有效方法的问题,提出基于深度强化学习的流排序和调度框架PSNDRL.该框架包括3个关键模块,即创建时间触发(Time-Triggered,TT)流之间关系图的预处理模块、挖掘和量化TT流之间复杂的相关关系并选择概率值最高的TT流的代理模块、进行TT流调度和奖励计算的环境模块,利用图卷积网络和强化学习从大量的TT流中智能探索流特征以及流之间的复杂相关关系对基于可满足性模理论(Satisfiability Modulo Theories,SMT)流调度算法求解时间的潜在影响.通过训练该框架,学习得到一个高效率的TT流策略排序网络,用于在利用SMT流调度算法调度TT流时进行TT流选择.通过与随机排序和基线排序方法进行对比,验证PSNDRL的有效性.结果表明:与随机排序方法的总调度时间、基线排序方法的最大总调度时间相比,PSNDRL的总调度时间分别减少了24.63%和25.95%.所提框架为提高时间敏感网络(Time Sensitive Networking,TSN)流调度效率的研究提供了新的方向.

济阳页岩油渗流机理及开发规律研究

济阳页岩油资源潜力巨大,但受复杂地质条件影响,对压裂后多尺度空间渗流机理及开发规律缺乏系统认识,规模效益开发难度大。为厘清济阳页岩油开发规律的内在机制,针对济阳页岩油多尺度裂缝发育特征,综合物理实验与数值模拟等多种手段,研究压裂后复合缝网的形成机制及组合模式,开展多尺度裂缝应力敏感、多级孔缝内流体非线性渗流、孔缝系统渗吸置换等多重介质空间渗流机理研究。依据压裂改造后多尺度缝网的分布及其渗流规律的差异性,建立了页岩油“易流-缓流-滞流”三区渗流模式,明确了济阳页岩油不同流动阶段的渗流特征与开发规律。研究结果表明:层理缝发育可改善储层物性条件,提高渗吸置换效率,降低启动压力梯度;弹性开发阶段随地层压力下降,渗流通道减小,缝网导流能力降低,具有明显的应力敏感性。济阳页岩油开发过程中,开发初期流态以易流区供液的裂缝线性流和裂缝椭圆流为主;开发中期缓流区向易流区供能,流态转变为地层椭圆流;开发后期滞流区内的页岩油逐渐动用,流态转变为边界控制流。受地质条件和生产制度影响,不同水平井能量变化、含水率下降和产量变化规律具有较大差异。合理优化闷井时间和生产制度,能够保证渗吸置换效果,高效利用地层能量,提高页岩油产能。

基于最佳预后元模型的颗粒污垢特性全局敏感性分析

通过敏感性分析可识别出重要变量和无关变量,有效筛选数据降低模型复杂程度,并辅助优化设计。以内置转子传热管内的颗粒污垢为研究对象,采用欧拉-欧拉模型和颗粒污垢模型进行数值实验获取训练数据空间,基于最佳预后元模型开展全局敏感性分析,定量比较了颗粒直径、颗粒浓度、入口流速和入口温度的影响程度。对颗粒污垢四种沉积速率分析表明,入口温度对扩散沉积和热泳沉积的影响最显著,总影响分别为65.4%、58.6%;颗粒直径对湍流泳沉积和重力沉积的影响最明显,总影响分别为53.9%、75.0%。在此基础上,进一步分析了沉积率和污垢热阻的总影响、主影响及交互影响。结果表明:颗粒直径对沉积率和污垢热阻的影响均最大,总影响分别为52.7%、60.2%,各输入变量对沉积率和污垢热阻的交互影响的和分别为59.7%、42.5%,且随着四个输入变量的增加,沉积率和污垢热阻均增大。颗粒直径是影响内置转子传热管颗粒污垢问题的首要因素,在换热器设计中应予以重点考虑,其次是流体温度与流速。

高温致密砂砾岩储层盐敏及盐析损害机理

中国渤海湾盆地广泛分布特低渗致密砂砾岩油气藏,与常规砂岩储层相比,致密砂砾岩储层具有黏土矿物丰富,溶蚀孔隙及微裂缝发育且非均质性强等特点,注入流体侵入容易诱发储层损害,堵塞孔喉,降低储层渗流能力,阻碍油气井稳产。以BZ19-6井区砂砾岩储层井下岩心为例,分别依据行业标准法和高温高回压稳态法开展储层盐敏损害室内实验评价,基于扫描电镜分析了敏感性矿物和盐类矿物的类型及赋存特征。实验结果表明:储层盐敏程度为中等偏强~强;岩心渗透率越低,盐析对储层的孔隙度和渗透率的损害程度越大,建议对于渗透率小于0.1 mD、储层温度高于100℃的致密岩心,推荐应用高温高回压稳态法评价储层流体敏感性更具优势。研究区黏土矿物以丝片/丝缕状伊利石、蚀变高岭石及伊/蒙间层矿物为主,主要呈栉壳式、分散充填、搭桥等方式赋存于溶蚀孔隙,是储层盐敏的主要因素。高温环境地层水加速蒸发,易导致近井带盐析,盐类矿物主要为钾盐和石盐,赋存于矿物颗粒表面和孔隙壁面易堵塞微细孔喉;地层水静态蒸发可溶盐析出堵塞致密孔喉、动态驱替盐晶运移堵塞喉道及盐析弱化岩石力学强度,导致微粒运移是致密砂砾岩盐析损害的主要机理。推荐使用KCl-饱和盐水聚磺钻井液和两性离子聚合物钻井液技术,通过降低钻井液侵入和抑制盐类在钻井液中的结晶和成核,从而降低储层盐敏损害。

非达西效应下瞬态承压无压转换数值解

为了研究承压含水层中不稳定承压无压完整井渗流转换机制,提出了一个考虑非达西效应的数值模型。利用Izbash方程描述了比流量与水力梯度之间的非线性关系,并通过有限差分法对模型进行求解。通过与达西渗流模型进行比较,验证了所提出模型的可靠性。结果表明,非达西指数、准水力渗透系数及单位储水量与非承压区的发育和含水层的降深之间呈负相关关系,这是由湍流程度的增大加速了对抽水井的补给所致。通过敏感性分析发现,降深对非达西指数、准水力渗透系数较为敏感,但对弹性储水系数和重力储水系数等不敏感。