Investigation on Mechanisms of Polymer Enhanced Oil Recovery by Nuclear Magnetic Resonance and Microscopic Theoretical Analysis

Polymer flooding is an efficient technique to enhance oil recovery over water flooding. There are lots of discussions regarding the mechanisms for polymer flooding enhancing oil recovery. The main focus is whether polymer flooding can increase sweep efficiency alone, or can increase both of sweep efficiency and displacement efficiency. We present a study on this problem. Oil displacement experiments on 4 natural cores show that polymer flooding can increase oil recovery efficiency by more than 12% over water. Moreover, photos are taken by the nuclear magnetic resonance （NMR） method both after water flooding and after polymer flooding, which show remaining oil saturation distribution at the middle cross section and the central longitudinal section. Analyses of these photos demonstrate that polymer flooding can increase both sweep efficiency and displacement efficiency.     

应用核磁共振进行聚驱后泡沫驱油特性研究

采用并联岩心进行聚驱后泡沫驱油实验,利用核磁共振技术,对驱替后岩心的不同直径孔隙内的流体分布进行了研究,得到了水驱、聚合物驱、泡沫驱替阶段的驱出油的孔径范围以及剩余油分布.实验结果表明,与水驱和聚合物驱相比,泡沫驱增大了波及的孔径的范围.泡沫可以在水驱和聚驱易发生窜流的大孔径通道形成封堵,从而波及到了水驱和聚驱未波及到的孔径,不但大幅度的提高了低渗岩心的采收率,也驱出了部分高渗岩心的小孔径的油.     

黏弹性聚合物驱驱替动态与不同注入参数分析

基于质量守恒定律,建立三相五组分考虑聚合物弹性增黏、降低残余油和稠油黏弹性效应的聚合物驱数学模型,并采用IMPES方法进行求解.计算分析表明,黏弹性聚合物驱可降低残余油饱和度,增加驱油体系黏度,提高原油采收率;采收率随注入浓度增大先迅速增加后趋于稳定,最优值为2 000 mg·L^-1;随注入速度先增加后降低,存在最优值;随聚合物段塞增大先迅速增加后缓慢增加并趋于稳定,最佳注入量约为0.6 PV;随原油松弛时间增加呈线性增加.     

超临界水驱超稠油提高采收率热物理特性研究

超稠油资源的高效开发对于提高石油供给和保障我国石油安全意义重大。针对深层超稠油资源由于原始地层压力高、原油黏度大导致常规蒸汽驱无法有效开发的问题,本文提出超临界水驱开发深层超稠油的新思路。本文首先研制了超临界水驱油提高采收率实验平台,研发的管式填砂岩心模型能够模拟岩心升温和驱替的同步过程,然后开展了超临界水驱、蒸汽驱和热水驱对比实验研究,实验结果表明,相对于蒸汽驱,超临界水驱能显著提高采收率并具有更高的热效率,25MPa、400℃超临界水驱鲁克沁超稠油的采收率达到97.07%;获得了超临界水驱过程的温度场和驱替压差变化规律,发现了超临界水超覆现象,与蒸汽超覆相比,超临界水超覆发生晚且持续短,可扩大波及范围,提高采收率。     

Enhanced (13)C PFG NMR for the study of hydrodynamic dispersion in porous media

PFG NMR methods are frequently used as a means of probing both coherent and incoherent molecular motions of fluids contained within heterogeneous porous media. The time scale over which molecular displacements can be probed in a conventional PFG NMR experiment is limited by the relaxation characteristics of (1)H - the nucleus that is typically observed. In multiphase systems, due to its sensitivity to susceptibility gradients and interactions with surfaces,(1)H signal is frequently characterized by rapid T(1) and T(2) relaxation. In this work, a heteronuclear approach to PFG NMR is demonstrated which allows the study of molecular displacement over extended time scales (and, consequently, length scales) by exploiting the longer relaxation time of (13)C. The method presented employs the DEPT technique of polarization transfer in order to enhance both the sensitivity and efficiency of (13)C detection. This hybrid coherence transfer PFG technique has been used to acquire displacement propagators for flow through a bead pack with an observation time of up to 35 s.     

摩擦导致的聚合物表层微观结构改变

应用大规模分子动力学方法, 模拟了锥形探头在非晶态聚合物薄膜表面的滑动摩擦过程, 研究了摩擦导致的聚合物薄膜表层微观结构改变, 以及探头与基体间黏着作用、滑动速度和分子链长度对基体表层微观结构改变的影响. 当探头与基体之间为黏着作用时, 摩擦导致基体表面滑痕区域的键取向沿滑动方向重新取向, 导致表层分子链回转半径沿滑动方向伸长, 并且这些表层微观结构的改变程度随滑动速度的减小而增大. 在摩擦导致结构改变的过程中, 链端单体和链中单体的贡献作用不同, 形成了不同的分子链拉伸变形机制. 当样本缠结度较大或探头滑动速度较小时, 相比于链中单体, 探头对链端单体的拖曳作用使更多分子链发生拉伸变形. 研究还发现, 在探头与聚合物薄膜系统中, 使薄膜表层微观结构发生改变是摩擦能量耗散的重要途径.     

基于VOF方法的水驱油藏孔隙尺度剩余油分布状态研究

准确认识多孔介质内水驱剩余油的微观赋存状态对于改善高含水油田水驱开发效果,提高水驱采收率具有重要意义。在对Volume of Fluid (VOF)方法验证的基础上,充分利用其追踪两相界面动态变化、再现微观渗流物理过程的优势,开展特高含水期砂岩油藏物性条件、驱替方式对剩余油微观赋存特征和采收率的影响研究。通过分析典型孔隙结构的微观渗流特征和剩余油受力情况,揭示不同类型微观剩余油的动用机制和规律：水湿条件下驱替速度的增大和驱替方向的改变会使得微观剩余油分布较为分散且采收率得到不同程度的提高;油湿及高黏度比条件下毛管阻力、黏滞力较大,剩余油多以簇状和多孔状聚集分布,采出程度相对较低。     

How Does van der Waals Confinement Enhance Phonon Transport?

We study the mechanism of van der Waals(vdW)interactions on phonon transport in atomic scale,which would boost developments in heat management and energy conversion.Commonly,the vdW interactions are regarded as a hindrance in phonon transport.Here we propose that the vdW confinement can enhance phonon transport.Through molecular dynamics simulations,it is realized that the vdW confinement is able to make more than two-fold enhancement on thermal conductivity of both polyethylene single chain and graphene nanoribbon.The quantitative analyses of morphology,local vdW potential energy and dynamical properties are carried out to reveal the underlying physical mechanism.It is found that the confined vdW potential barriers reduce the atomic thermal displacement magnitudes,leading to less phonon scattering and facilitating thermal transport.Our study offers a new strategy to modulate the phonon transport.     

质子交换膜燃料电流道淹没与传质强化

在地面常重力环境下,采用透明电池可视化方法研究了质子交换膜燃料电池阳极和阴极的流道淹没现象。分别研究了阳极和阴极反应物流量对电池内部传质和电池性能的影响。结果表明,电池阴极的淹没区域比阳极大,由电极淹没引起的气体传质受限和电化学反应受限主要发生在阴极。提高反应物流量能够强化气体传质并提高电池性能,并且提高电池阴极侧反应物流量比提高阳极侧反应物流量对提高电池性能更有效。本文工作为进一步开展微重力环境中的燃料电池实验提供了比较依据。     

聚合物强化泡沫驱数学模型及其应用

基于泡沫组分物质守恒原理,考虑泡沫生成、破灭、运移现象,建立聚合物强化泡沫驱渗流的多组分数学模型,有效反映油相消泡和聚合物稳泡作用机理,采用自适应隐式方法进行求解.通过拟合泡沫驱替实验结果,验证数学模型的有效性.对某油区泡沫先导试验区进行跟踪数值模拟,分析泡沫驱渗流特征,结果表明,强化泡沫体系能够在地层稳定存在,并不断向生产井推进,从而大幅度提高原油采收率.     

Molecular simulations of phenol and ibuprofen removal from water using multilayered graphene oxide membranes

We present here non-equilibrium molecular dynamic simulations concerning the separation of phenol and ibuprofen as impurities compounds (ICs) in water by novel graphene oxide (GO) membranes. The coupling between water permeability and impurity rejection is studied as a function of membrane thickness and concentration, focusing on the underlying molecular phenomena. Results show that water permeability decreases as the number of layers increases. Moreover, molecular sieving can be achieved by tuning the number of GO layers and the surface chemistry of the sheet: water flow through layers is up to 20% faster than that in graphene layers, because of strong hydrogen bonded interactions with the oxygenated groups. Analysis of the simulation results suggests that upon adsorbing on the GO surface, the translational motion of ICs in water would be supressed. Nevertheless, hydrophilicity affects the permeability for membranes with high O/C ratio, owing to these strong hydrogen bonds. Furthermore, 100% rejection for the ICs can be obtained for most of the GO membranes with four layers. This study elucidates the important role of hydrophilic interactions in GO membranes to become ideal candidates for removal of organic pollutants from water, showing the applicability of molecular simulations to obtain molecular insights into this problem.     

An adaptive high-order minimum action method

In this work, we present an adaptive high-order minimum action method for dynamical systems perturbed by small noise. We use the hp finite element method to approximate the minimal action path and nonlinear conjugate gradient method to solve the optimization problem given by the Freidlin–Wentzell least action principle. The gradient of the discrete action functional is obtained through the functional derivative and the moving mesh technique is employed to enhance the approximation accuracy. Numerical examples are given to demonstrate the efficiency and accuracy of the proposed numerical method.     

利用磁共振录井技术定量评价水淹层

产水率是划分水淹级别的关键参数,如何通过含水饱和度计算产水率是进行水淹层评价工作要解决的主要问题. 通过测定油-水相对渗透率的注水实验制备出不同产水率的岩样,分析并研究不同产水率下的磁共振录井谱图特征和分析参数响应特征,可探讨利用磁共振录井资料评价水淹级别的可行性. 该工作根据密闭取心井的试油资料和相渗曲线,提出了利用磁共振含水饱和度计算地层产水率经验公式的方法, 并进行了生产应用. 结果表明,利用磁共振录井技术评价水淹层的符合率达到了86%,证明了该项技术在快速、定量评价水淹层和划分水淹级别的良好应用前景.     

复杂微通道内非混相驱替过程的格子Boltzmann方法

本文采用改进的基于伪势模型的格子Boltzmann方法研究复杂微通道内的非混相驱替问题.这种方法克服了原始伪势模型中计算结果对网格步长的依赖.首先用Laplace定律验证模型的正确性,然后用该方法研究壁面润湿性、粗糙结构、黏性比以及距离对非混相驱替过程的影响.模拟结果表明:与壁面粗糙结构和黏性比相比,壁面润湿性的影响是决定性的因素.随着接触角的增加,驱替效率增加,当接触角大于某一值后,驱替效率不再变化;随着黏性比的增加,驱替效率增加;而壁面粗糙性对驱替过程的影响较复杂,只有凸起半圆的半径在一定范围内增加时,驱替效率增加;距离较小时将促进驱替过程.     

Magnetic resonance imaging study of complex fluid flow in porous media: flow patterns and quantitative saturation profiling of amphiphilic fracturing fluid displacement in sandstone cores

Magnetic resonance imaging is used to follow the removal process of a visco-elastic surfactant (VES) fracturing fluid in Bentheimer sandstone cores at typical reservoir temperatures (T=333 K). Two displacing fluids were investigated, a Gadolinium doped water phase (1M NaCl solution), and a Gadolinium doped hydrocarbon phase (Mineral Spirits). In addition to flow characteristics obtained by conventional core-flooding, i.e., the macroscopically averaged volumetric flow rates and differential pressures, we have also measured the saturation profiles and characteristic displacement patterns during all stages of the removal process. To acquire these data we have used quantitative one-dimensional chemically specific profiling along with fast two-dimensional imaging experiments while flooding Bentheimer sandstone cores in situ in the spectrometer. Our results show that both displacement processes (complex fluid displaced by water or hydrocarbon phase) are dominated by the large viscosity contrasts present. However, distinct differences were found between the displacement characteristics of water and hydrocarbon, which confirmed the sensitivity of the complex fracturing fluid to the displacing fluid.     

Adsorption of model charged proteins on charged surfaces with grafted polymers

The adsorption of model charged proteins on charged surfaces with and without grafted polymers is studied using a molecular approach. The ability of the polymer layer to reduce the amount of proteins adsorbed on top of the surface (primary adsorption) and at the same time to increase the adsorption of the proteins on top of the polymer layer (secondary adsorption) is presented. It is found that charging the free ends of the chains can result in an efficient way to enhance adsorption at the tip of the brush. Increasing the surface coverage of the polymers with charged free ends enhances the amount of proteins adsorbed at the tip of the polymer layer, while at the same time strongly reduces the number of proteins adsorbed directly onto the surface. The interplay between the attractive van der Waals protein-surface interactions, the steric polymer-protein interactions and the effect of the electrostatic interactions in determining the final adsorption is discussed. The manipulation of solution conditions to tune the amount of secondary adsorption is presented.     

水驱油藏中原油极性物质对吸附和润湿性影响的分子模拟

为了研究水驱油藏中原油极性物质的吸附机理及其对油藏表面润湿性的影响,构建以石英为代表的砂岩岩石骨架模型,己烷为代表的非极性物质模型和以甲苯、胶质和沥青质为代表的极性物质模型,运用分子模拟方法研究4种原油组分和水分子在砂岩油藏表面竞争吸附过程和润湿状态。结果表明：水与4种原油组分在石英矿物表面竞争吸附时,原油中的非极性物质会比极性物质更加容易脱附。极性物质会随着时间的变化逐渐吸附在矿物表面,非极性的物质会随着时间变化逐渐远离矿物表面。吸附过程中静电力起吸附作用,范德华力起排斥作用。最后结合润湿性实验结果,从机理上解释了不同原油组成对润湿性的影响,即原油组分中极性物质含量越高,胶质沥青质含量越大,岩石表面油湿性越大,且水驱过程中润湿性向亲水方向变化越难。结论对提升水驱油藏采收率影响因素的认识有重要意义。     

Structure of a tethered polymer under flow using molecular dynamics and hybrid molecular-continuum simulations

We analyse the structure of a single polymer tethered to a solid surface undergoing a Couette flow. We study the problem using molecular dynamics (MD) and hybrid MD-continuum simulations, wherein the polymer and the surrounding solvent are treated via standard MD, and the solvent flow farther away from the polymer is solved by continuum fluid dynamics (CFD). The polymer represents a freely jointed chain (FJC) and is modelled by Lennard-Jones (LJ) beads interacting through the FENE potential. The solvent (modelled as a LJ fluid) and a weakly attractive wall are treated at the molecular level. At large shear rates the polymer becomes more elongated than predicted by existing theoretical scaling laws. Also, along the normal-to-wall direction the structure observed for the FJC is, surprisingly, very similar to that predicted for a semiflexible chain. Comparison with previous Brownian dynamics simulations (which exclude both solvent and wall potential) indicates that these effects are due to the polymer–solvent and polymer–wall interactions. The hybrid simulations are in perfect agreement with the MD simulations, showing no trace of finite size effects. Importantly, the extra cost required to couple the MD and CFD domains is negligible.     

采用密度泛函理论与分子动力学对聚甲基丙烯酸甲酯双折射性的理论计算

双折射性是各种光学材料的重要性能之一,具有高双折射率的光学材料在诸多研究及工业领域的应用越来越广泛.然而,作为常用的光学薄膜及光波导材料之一的聚合物材料的双折射性通常却很弱,只能通过实验对其双折射率进行大致的表征,缺乏对其双折射率的系统性理论计算,从而限制了提高聚合物双折射性的研究.本文建立了从聚合物的单体分子结构到多分子链的系统性的双折射率理论计算方法,并借助此方法研究了导致聚合物弱双折射性的限制因素.以聚甲基丙烯酸甲酯(PMMA)为研究对象,运用密度泛函理论研究了其本征双折射率,这里的本征双折射率是指分子链完全取向时其单体单元的双折射率.计算结果表明其本征双折射率高达0.0738左右,并且通过计算给出了PMMA单体单元的平均双折射率色散曲线.采用分子动力学方法研究了该聚合物(包含20个分子链)的材料双折射率.理论计算结果表明,尽管该聚合物具有较大的本征双折射率,但是由于聚合物中分子链取向度极低,聚合物材料最终表现出来的双折射率只有0.00052.本文建立的研究方法及研究结果为研究增强聚合物材料双折射性提供了理论依据.     

Exciton self-trapping in molecular media with an elastic dipole moment

Exciton self-trapping in a molecular medium is considered within a self-consistent model taking into account the change in the dipole moment as a result of a displacement of molecules and the resonance interaction with an electromagnetic field. New mechanisms and specific features of the formation of localized structures in quasi-one-dimensional molecular structures are investigated. It is shown that the dependence of the dipole moment on molecular vibrations leads to new conditions for exciton self-trapping and intrinsic optical bistability, as well as for the formation of electromagnetically induced transparency. The theory proposed is used to explain the specific features of exciton self-trapping in a conjugated polymer and J aggregates of dyes under the action of an external laser field.