Snap‐off of a liquid drop immersed in another liquid flowing through a constricted capillary

Emulsions are encountered at different stages of oil production processes, often impacting many aspects of oilfield operations. Emulsions may form as oil and water come in contact inside the reservoir rock, valves, pumps, and other equipments. Snap‐off is a possible mechanism to explain emulsion formation in two‐phase flow in porous media. Quartz capillary tubes with a constriction (pore neck) served to analyze snap‐off of long (“infinite”) oil droplets as a function of capillary number and oil‐water viscosity ratio. The flow of large oil drops through the constriction and the drop break‐up process were visualized using an optical microscope. Snap‐off occurrence was mapped as a function of flow parameters. High oil viscosity suppresses the breakup process, whereas snap‐up was always observed at low dispersed‐phase viscosity. At moderate viscosity oil/water ratio, snap‐off was observed only at low capillary number. Mechanistic explanations based on competing forces in the liquid phases were proposed. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

田菁冻胶在毛细管及多孔介质中滑移效应研究

本文用实验方法研究了田菁冻胶压裂液在毛细管和多孔介质中的流动特性,求得相应的滑移效应,提出本构方程及C·H.B.模型,并得以验证.     

Propagation of Surfactant-Dispersed Multiwalled Carbon Nanotubes in Porous Media

Understanding the transport of carbon nanotubes in porous media is essential to their applications in subsurface reservoirs, e.g., delivering catalysts or chemicals to targeted formations. In this study, a series of laboratory experiments are conducted to explore the transport of surfactant-dispersed multiwalled nanotubes (MWNT) in different porous media in flow-through columns at elevated electrolyte levels. Noncovalent bonding of ethoxylated alcohols adsorbed on the MWNT surface provides them with outstanding dispersion stability and excellent transport properties in a crushed-limestone sand pack. Superior transport performance in silica sand is obtained with binary nonionic–anionic surfactant formulations, which provide both steric repulsion and electrostatic repulsion between nanoparticle–nanoparticle and nanoparticle–sand surface. The mobility of MWNT suspensions are further investigated in the exposure to multiphase flow, e.g., with residual oil present, or coinjected with air into the sand pack. Coinjecting surfactant-dispersed MWNT suspensions with air (i.e., MWNT-stabilized foams) has hardly any impact on their propagation; retention in the sand pack remains quite low. With the presence of oil in the sand pack, the transport of MWNT suspensions is highly dependent on the type of surfactants used as the dispersant. For surfactants that achieved modest interfacial tension (IFT) reduction, the injected MWNT suspension bypasses the oil phase, and little impact on retention is observed. When the dispersant surfactant is also adjusted for an ultralow IFT condition, greater MWNT retention in the porous medium is observed because surfactants detach from the MWNT surface and aggressively partition to the oil/water interface, allowing the MWNT to flocculate and become deposited in the porous medium.     

多孔介质中流动泡沫的压力分布计算

将多孔介质简化为一簇变截面毛细管组成的毛细管束,根据多孔介质的颗粒直径、颗粒排列方式、孔喉尺度比以及束缚水饱和度,计算出变截面毛细管的喉道半径和孔隙半径。在考虑多孔介质喉道和孔隙中单个气泡的受力和变形基础上,利用质量守恒定理和动量守恒定理,推导出单个孔隙单元内液相的压力分布和孔隙单元两端的压力差计算公式,最终得到多孔介质的压力分布以及多孔介质中泡沫当量直径计算方法。利用长U型填砂管对多孔介质中稳定泡沫的流动特性进行了实验研究,并对实验结果和计算结果进行了对比。结果表明:稳定泡沫流动时多孔介质中的压力分布呈线性下降,孔喉结构和泡沫干度是影响泡沫封堵能力的主要因素;泡沫的封堵能力随泡沫干度的增加而先增加后降低,在泡沫干度为85%时达到最强封堵能力。     

泡沫薄膜液在直管内的流变学特性

针对泡沫液在多孔介质内的流动特点,对泡沫薄膜液在直管内的流变学特性进行了实验研究。按单相幂律流体假设,获得二氧化碳及氮气泡沫薄膜液的表观黏度数据。结果表明：泡沫薄膜液具有较大表观黏度并呈现剪切变稀的非牛顿流体特性。由于水溶性影响,二氧化碳泡沫液的表观黏度要小于氮气泡沫液。利用量纲分析法确定量纲1参数,对泡沫薄膜液的流变学特性进行了量纲1分析并给出基于两相流动分析的阻力模型。     

The flow and displacement in porous media of fluids with yield stress

We study the mobilization and subsequent flow in a porous medium of a fluid with a yield stress, modeled as a Bingham plastic. We use single-capillary expressions for the mobilization and flow in a pore-throat, and a pore-network model that accounts for distributed yield-stress thresholds. First, we extend the statistical physics method of invasion percolation with memory, which models lattice problems with thresholds, to incorporate dynamic effects due to the viscous friction following the onset of mobilization. Macroscopic relations between the applied pressure gradient and the flow rate for single-phase flow are proposed as a function of the pore-network microstructure and the configuration of the flowing phase. Then, the algorithm is applied to model the displacement of a Bingham plastic by a Newtonian fluid in a porous medium. The results find application to a number of industrial processes including the recovery of oil from oil reservoirs and the flow of foam in porous media.     

Trapping of the non-wetting phase in an interacting triangular tube bundle model

An interacting triangular tube bundle model is developed using capillaries of equilateral triangle cross sections. In addition to pressure equilibration among the capillaries, the non-circular tubes allow the wetting phase to reside in the corners and flow continuously in the entire model. An interacting-serial type model is constructed with step changes of tube size along the model, while the total cross-section of the model is kept constant. This model includes trapping of oil which is absent in traditional tube bundle models. Trapping of non-wetting phase in the model in imbibition processes is simulated. The relationship between the residual oil saturation and the complete capillary number CA is investigated. The simulation results obtained by this model are consistent with the results reported in literature of both experimental studies, using actual porous media, and simulations in pore-scale network models. The effects of the tube size, tube size distribution and viscosity ratio on the magnitude of entrapment are also studied using this tube bundle model.     

The performance of polymer solutions in enhanced oil recovery: studies on their rheological,interfacial, and porous media behaviors

Four polymeric solutions based on xanthan, high and low molecular weight sulfonated polyacrylamides, and hydrolyzed polyacrylamide were prepared in aqueous solutions and their behaviors in enhanced oil recovery applications were investigated. The effect of thermal aging on polymer solutions was evaluated through rheological measurement. Pendant drop method was also used for measuring the interfacial tension (IFT) between crude oil and brine containing different polymer solutions. Moreover, the zeta potential of the oil reservoir particles treated with oil and polymer was determined by electrophoresis method in a nano-zeta meter instrument. In addition, sand pack and core flooding setup were used for evaluating the effectiveness of the polymer solutions in porous media. Polymer solutions displayed non-Newtonian behavior in almost the whole range of the shear rate applied; a shear thinning behavior was seen. Furthermore, the aging of polymers in formation water decreased the shear viscosity of all the polymers. The oil/water IFT decreased by the addition of polymers to water. The effect of xanthan polymer on zeta potential value was greater than that of the three acrylamide-based polymers. According to sand pack tests, by increasing the polymer concentration, the incremental oil recovery initially increased up to a polymer concentration of 3,500 ppm and then started to fall. Recovery factor increased from 50 to 65 % using the polymer solution in core flooding experiments. By increasing the injection rate from 0.2 to 3 mL/min, the injected fluid had less time to sweep the pores and consequently the amount of recovered oil decreased.     

Effect of oil viscosity on recovery processes in relation to foam flooding

Laboratory experiments were conducted to determine the effect of oil viscosity on the oil-recovery efficiency in porous media. The pure surfactants (i.e., sodium dodecyl sulfate and various alkyl alcohols) were selected to correlate the molecular and surface properties of foaming solutions with viscosity, and the recovery of oil. Oil-displacement efficiency was measured by water, surfactant-solution and foam-flooding processes, which included 2 types of foams (i.e., air foam and steam foam). A significant increase in heavy-oil recovery was observed by steam foam flooding compared with that by air foam flooding, whereas for light oils, the steam foam and air foam produced about the same oil recovery. An attempt was made to correlate the chain-length compatibility with the surface properties of the foaming agents and oil-recovery efficiency in porous media. For mixed foaming systems (C₁₂ SO₄ Na + C_n H_2n+1 OH), a minimum in surface tension, a maximum in surface viscosity, a minimum in bubble size and a maximum in oil recovery were observed when both components of the foaming system had the same chain length. These results were explained on the basis of thermal motions (i.e., vibrational, rotational and oscillational) and the molecular packing of surfactants at the gas-liquid interface. The effects of chain-length compatibility and the surface properties of mixed surfactants are relevant to the design of surfactant formulations for oil recovery under given reservoir conditions.     

Investigation on Foam Self‐Generation Using In Situ Carbon Dioxide (CO2) for Enhancing Oil Recovery

In situ carbon dioxide (CO₂) foam flooding has proved to be economically feasible in the oil field, but its self‐generation behavior in the bulk scale/porous media is far from understood. In this study, the optimum in situ CO₂‐foaming agent was first screened, and then in situ foam was investigated in the bulk. In situ foam flooding was conducted to evaluate the displacement characteristics and enhanced oil recovery of this system. The results showed that the foaming agent comprising 0.5% sodium dodecyl sulfonate (SDS) + 0.5% lauramido propyl hydroxyl sultaine (LHSB) gave the best foam properties and that the in situ CO₂ foam with a slow releasing rate is effective both in bulk scale and in porous media, allowing a considerable enhancement of oil recovery in sand packs with different permeabilities.     

THE EFFECTS OF MEDIUM THICKNESS ON THE ISLAND SIZE DISTRIBUTION IN IMMISCIBLE DISPLACEMENT FLOW IN POROUS MEDIA

The invasion percolation algorithm is used to simulate two-fluid immiscible displacement of a wetting fluid by a non-wetting fluid in various porous media represented by two-dimensional and three-dimensional networks of interconnected capillaries. Trapping of the displaced fluid occurs, thereby creating isolated islands. The effects of the thickness of the porous medium on the island size distribution are studied for capillary displacements for the case in which buoyancy effects are negligible. It was found in a previous study that the number of islands of size s scales approximately as s~" in two-dimensional porous media, where a is a function of the fluid viscosity ratio. The present work reveals that there is a cross-over behavior between the two-dimensional and the three-dimensional problems.     

Mathematical models for the drying of rigid porous materials

This paper presents a resume of literature on theories and mathematical models for drying of rigid porous materials. Key work on drying by soil physicists has been neglected in the engineering drying literature. We have included these works here to bring this literature to the attention of engineers. A new and general model for moisture and energy transport in rigid porous media during drying is presented. It is demonstrated that under certain simplifying assumptions, the general model reduces to less general models which have previously been proposed. Experimental and simulation results are given for the drying of Valentine sand. Under the drying conditions studied, the drying rate during the falling rate period is controlled by the capillary flow of water to an evaporation zone in the porous media. The models simulated here are of varying complexity and rigor. The capabilities and limitations of these models are discussed.     

Formation of liquid bridges between porous matrix blocks

It is widely accepted that, in fluid flow and transport in fractured porous media, there exists some degree of block‐to‐block interaction that may lead to capillary continuity. The formation of liquid bridges causing interaction between blocks will affect oil recovery from naturally fractured reservoirs. However, the accurate modeling of the growth and detachment of liquid bridges that may cause capillary continuity between matrix blocks remains a controversial topic. In an attempt to improve our understanding of the problem, a mechanistic model is developed in this work for the formation of liquid bridges between porous blocks. The proposed model considers growth and detachment of pendant liquid droplets perpendicular to the horizontal and smooth fracture between porous matrix blocks. The liquid bridge model is then coupled with various upscaled fracture capillary pressure models to study the liquid bridge formation process. An expression is obtained that relates the commonly used fracture capillary pressure to the critical length of the liquid element. Results based on various fracture capillary pressure models reveal that the threshold Bond number is an important parameter in the formation of liquid bridges. We introduce a simple mechanistic model for the formation of liquid bridges in a horizontal fracture between two porous blocks, advancing our understanding of the two‐phase flow in fractured porous media. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

Preparation and characterization of polyacrylamide nanomicrospheres and its profile control and flooding performance

In this study, a new profile control and flooding agent “polyacrylamide nanomicrospheres” with particle size of 120–180 nm was prepared by inverse microemulsion polymerization. The viscoelasticity of polyacrylamide nanomicrospheres and the swelling property of polyacrylamide nanomicrospheres in aqueous solution were characterized. Using sand pack models, the profile control and flooding performance of polyacrylamide nanomicrospheres was studied. The results show that the polyacrylamide nanomicrospheres have better elasticity; the polyacrylamide nanomicrospheres have obvious swelling property, which depends on the concentration of NaCl and temperature; the polyacrylamide nanomicrospheres can plug sand pack effectively and have better ability of transporting and plugging in porous media; the polyacrylamide nanomicrospheres prefer to plug high permeability layer selectively so as to increase the swept volume and enhance oil recovery of low permeability layer and low permeability area in high permeability layer; the polyacrylamide nanomicrospheres can enhance oil recovery by 11–14%. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Dynamic modeling of drainage through three-dimensional porous materials

The interplay of viscous, gravity and capillary forces determines the flow behavior of two or more phases through porous materials. In this study, a rule-based dynamic network model is developed to simulate two-phase flow in three-dimensional porous media. A cubic network analog of porous medium is used with cubic bodies and square cross-section throats. The rules for phase movement and redistribution are devised to honor the imbibition and drainage physics at pore scale. These rules are based on the pressure field within the porous medium that is solved for by applying mass conservation at each node. The pressure field governs the movement and flow rates of the fluids within the porous medium. Film flow has been incorporated in a novel way. A pseudo-percolation model is proposed for low but non-zero capillary number (ratio of viscous to capillary forces). The model is used to study primary drainage with constant inlet flow rate and constant inlet pressure boundary conditions. Non-wetting phase front dynamics, apparent wetting residuals (S_wr), and relative permeability are computed as a function of capillary number (N_ca), viscosity ratio (M), and pore-throat size distribution. The simulation results are compared with experimental results from the literature. Depending upon the flow rate and viscosity ratio, the displacement front shows three distinct flow patterns—stable, viscous fingering and capillary fingering. Capillary desaturation curves (S_wr vs. N_ca) depend on the viscosity ratio. It is shown that at high flow rates (or high N_ca), relative permeability assumes a linear dependence upon saturation. Pseudo-static capillary pressure curve is also estimated (by using an invasion percolation model) and is compared with the dynamic capillary pressure obtained from the model.     

污水配制聚合物溶液稳定性及改进方法研究

以大庆萨南油田南二西和南三西区块为研究平台,首先通过研究由油田新鲜污水和曝氧污水配制的聚合物溶液的粘度稳定性受WDJ-1稳定剂的影响,分析了稳定剂的作用机理;随后,在60 cm长岩心上开展传输运移实验,研究了稳定剂对聚合物溶液在多孔介质里的流动性和传输性能的影响。实验结果表明,在大庆油田45℃低温油藏条件下,使用油田污水配制的聚合物溶液存在明显的化学降解作用;HPAM聚合物的热氧降解是因为自由基O·攻击聚合物造成聚合物链发生断裂,导致溶液粘度急剧降低;在新鲜污水和曝氧污水配制聚合物溶液中添加100~120 mg/L稳定剂,能明显提高聚合物粘度在油层条件下的长期稳定性,改善聚合物溶液在岩石多孔介质中的流动性和传输性能,进而确保污水聚合物驱具有较好的驱油效果。     

Capillarity in fibrous filter media: Relationship to filter properties

This work examines the wetting of a range of low packing density (high porosity), porous, fibrous media by mineral oils. The fibrous media were suspended above a vessel of oil, and the rate of imbibation of oil was measured by means of a balance under the oil and a load cell above the media. It was found that the height of the oil column within the media over time generally resembled the classical capillary rise curve. Capillary rise models were fitted to the data to predict an equivalent capillary diameter, dynamic contact angle, and height of the liquid column as time approaches infinity, using the known filter and oil properties. Different capillary models were examined, and it was found that the modified Washburn equation was the simplest model to use and produced an acceptable agreement between theory and experiment. It was found that the adjustment phase of the curve from the fibrous media was generally more rapid than for a typical capillary, presumably since the fibrous media can be wetted not only from directly below (as with a capillary), but also through the meniscus at the sides of the media. It was found that a linear correlation existed between the effective capillary diameter of the media, and the packing density of the media divided by the fibre diameter. The results appear to be relatively independent of the material type. These results allow capillary diameters to be determined for fibrous media from easily measured parameters, without the requirement of conducting wetting experiments or ‘bubble-point’ tests.     

复色多相聚合物/ 油/ 水分散体系的悬浮稳定性及分散稳定性

采用Ｓｔｏｋｅｓ落球模型研究了两相密度差对油／水分散体系悬浮稳定性的影响规律,考察了水相粘度及水相界面张力对油／水分散体系分散稳定性的影响。结果表明：复色多相分散体系的悬浮稳定性主要由两相密度差决定,当两相密度差降至０．５ｋｇ／ｍ３时,可以制得悬浮稳定性很好的复色多相分散体系。水相粘度增大,悬浮稳定性提高。水相界面张力对丙烯酸酯－聚氨酯油相形成的分散体系影响较大,当其界面张力大于６９．５×１０－３Ｎ／ｍ时,分散稳定性好。只要粒子间不易相互融结,形成的复色多相分散体系便不发生渗色现象。     

含湿率对多孔介质热导率测量准确性的影响

本文利用HotDisk热常数分析仪对不同含湿率时含湿沙的热导率进行测量研究,并对孔隙尺度水分形态、分布及演化过程进行了观察实验研究。研究发现,低含湿率（＜25%）情况下,介质的有效热导率难以准确测得。低含湿时孔隙内水分主要以孤立液桥形式存在,测试过程中,贴近探头附近的水分由于受探头加热发生蒸发扩散而逐渐减少,导致探头周围试样构成持续发生变化,因而测量得到的热导率准确性较差。含湿率较高时,孔隙内水分相互联通,测试时水分蒸发扩散速度相对较慢,且存在毛细回流现象,探头周围试样构成维持恒定,因此可以准确获得热导率。     

操作参数对三相卧螺离心机油水砂分离性能影响模拟及实验分析

首先提出一种新型可调溢流堰板式三相卧螺离心机主体结构，其内部设置了径向排油通道以及位置和大小可调节的溢流堰板。其次，使用计算流体力学软件Fluent、基于欧拉-欧拉多相流模型，对三相卧螺离心机流场及分离性能进行数值模拟，建立三维流域模型、进行网格划分及边界条件设定，对油相及固相浓度分布等进行分析。之后确定实验工艺流程图，搭建油水砂三相分离实验系统平台，建立三相分离实验系统装置，制定实验步骤进行实验研究及测量工作。分别从转鼓转速、处理量等研究了各自对固相回收率、油相回收率、油在滤饼中的损失及油在水中的损失等的影响规律，并从出砂含固、出油含油、出渣含油及出水含油质量浓度等方面对数值模拟结果进行实验验证。