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.

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.

Effects of physical parameter range on dimensionless variable sensitivity in water flooding reservoirs

The similarity criterion for water flooding reservoir flows is concerned with in the present paper. When finding out all the dimensionless variables governing this kind of flow, their physical meanings are subsequently elucidated. Then, a numerical approach of sensitivity analysis is adopted to quantify their corresponding dominance degree among the similarity parameters. In this way, we may finally identify major scaling law in different parameter range and demonstrate the respective effects of viscosity, permeability and injection rate.

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.

Analysis of key parameters sensitivity and calibration accuracy of signal timing algorithm

A theoretical sensitivity analysis of total lost timeand saturated flow rate is conducted based on the methodproposed in the Highway Capacity Manual （HCM）. Inaddition, the accuracy of the timing calculation algorithmsuggested in the HCM is verified using field data from threeintersections. It is demonstrated that there is a positivecorrelation between the estimation error rates of the signalcycle length and the phase lost time. Also, the estimated valueof saturated flow rate must meet the specific requirementsunder different saturated conditions to guarantee the accuracyof the signal cycle length. However, through analysis of fielddata collected on the discharge headway in three intersections,it is also found that, if the 4th vehicle is set as the initial spotfor the stable discharge headway, as is recommended in theHCM, the error of the phase lost time will be over 40% whenthe line length is over 10 vehicles. Moreover, the calculationerror for signal cycle length is not guaranteed to fall within the15% range when the length of line is over 15 vehicles. It issuggested that, to improve the applicability of the HCMmethod, a more accurate description of the distributedregularity of the discharge headway is necessary whencalibrating key parameters.

Comparative studies of serum-free media and detection techniques for <i>in vitro</i>drug sensitivity assessment of <i>Plasmodium falciparum</i>

Malaria continues to be a devastating disease. In a previous study, we formulated a chemically defined culture medium that is able to sustain the complete intraerythrocytic growth of Plasmodium falciparum. We tested the feasibility of using the medium (CDRPMI) as well as human serum-free media enriched with commercially available human-serum substitutes (GFSRPMI and ALBRPMI) to assess the drug sensitivity of P. falciparum, using chloroquine diphosphate (CQ) and dihydroartemisinin (DHART) as conventional antimalarial drugs. Growth inhibition was measured by four different methods: flow cytometry with SYBR Green I (FCM), microscopy (Giemsa method), enzymatic estimation of parasite lactate dehydrogenase (pLDH), and histidine-rich protein 2 (HRPII) determination. In drug sensitivity tests on asynchronous parasites cultured for 96 h in the presence of drugs, the dose-response curves were similar and differences in the 50% growth inhibition concentrations for the drugs, which were estimated by the four methods, were not statistically significant for the three culture media. The effect of the drugs on the growth of synchronous parasites at the ring stage was also assessed in micro-volume tests by three different methods of FCM: tracking fluorescent erythrocytes, schizont test, and merozoite test. Dose-response curves for the drugs were similar, and differences in the 50% growth inhibition concentrations were not statistically significant for CDRPMI and GFSRPMI. Thus CDRPMI as well as GFSRPMI and ALBRPMI can be similarly useful media for drug sensitivity testing of P. falciparum. The FCM, pLDH and HRPII estimations were fast and reliable detection methods, with FCM allowing schizont and merozoite tests to be performed with shorter periods of culture.

Hydrodynamics and Sensitivity Analysis of a Williamson Fluid in Porous-Walled Wavy Channel

In this work,a steady,incompressible Williamson fluid model is investigated in a porous wavy channel.This situation arises in the reabsorption of useful substances from the glomerular filtrate in the kidney.After 80%reabsorption,urine is left,which behaves like a thinning fluid.The laws of conservation of mass and momentum are used to model the physical problem.The analytical solution of the problem in terms of stream function is obtained by a regular perturbation expansion method.The asymptotic integration method for small wave amplitudes and the RK-Fehlberg method for pressure distribution has been used inside the channel.It is demonstrated that the forward flow becomes fast in the narrow region(at x=0.75),which dominates the upward flow inside the channel.To study the impact of model parameters on outputs,we applied normalized local sensitivity analysis and noticed that the most influential parameter for the longitudinal velocity profile is the dimensionless wave amplitude.The reabsorption parameter is sensitive for transverse velocity in the narrow region,and the Weissenberg number has a strong effect on the pressure inside the channel.Further,the least sensitive parameters for the velocity components and pressure have been identified.

Effect of resistance exercise on insulin sensitivity of skeletal muscle

Insulin resistance(IR)is the common pathophysiological basis of many metabolic diseases.IR is characterized by decreased glucose uptake in skeletal muscle and adipose tissue,especially in skeletal muscle.Skeletal muscle is the main target tissue of glucose uptake under insulin stimulation.Glucose uptake by skeletal muscle is complex,and it is controlled by many pathways.The PI3K/AKt/GSK-1 signaling pathway is not only the main pathway for insulin signal transduction but also an important mechanism for regulating blood glucose.From the binding of insulin to its receptors on the surface of target cells to the transportation of glucose from extracellular fluid to skeletal muscle,a series of signal transduction processes is completed,any of which potentially affects the physiological effects of insulin and leads to IR.Resistance exercise(RT)can reduce skeletal muscle IR and effectively improve blood glucose control and glycosylated hemoglobin level in patients with type 2 diabetes mellitus(T2DM).However,the exact mechanism by which RT improves skeletal muscle IR remains unclear.Therefore,this paper discusses the above problems by tracking the progress of the literature to deepen the correlation between RT and skeletal muscle insulin sensitivity and provide further evidence for the application of exercise therapy in IR.In conclusion,RT mainly improves insulin sensitivity of skeletal muscle by increasing muscle mass,microvascular blood flow,and glucose transporter-4 expression in skeletal muscle,as well as by reducing lipid accumulation and inflammation in skeletal muscle.Thus,it is potentially useful in the prevention and treatment of T2DM.

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。

Differences of Gas Lift Design between Deviated and Vertical Wells and the Analysis of Sensitivity Parameters

尽管气举越来越多地被应用到大斜度井、水平井的举升采油中,但倾斜井气举设计与直井气举设计存在什么差异,这些差异随倾斜角度的增大将怎样变化,以及哪些气举设计所需参数对这种差异比较敏感,即如何对倾斜井气举设计所需参数进行合理选择,以便对倾斜井气举设计进行优化的研究较少,这也一直是倾斜井合理气举设计的难点问题。鉴于此,笔者以某油田一口倾斜井为例,通过实测数据进行了倾斜井产能预测方法优选和多相管流压力计算方法优选,然后在该基础上采用等套压降气举设计方法对比分析了倾斜井气举设计与同等条件下直井气举设计的差异,并逐一分析了各种气举设计所需重要参数分别取不同值时气举设计注气深度和产量随井斜角度的变化规律,从而得到了倾斜井气举设计的敏感性参数,可为倾斜井气举设计的参数优化和调整提供参考依据,是倾斜井气举高效生产的有力保障。

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。