【作者】 顾春元；

【导师】 狄勤丰；

【作者基本信息】 上海大学 ， 工程力学， 2008， 博士

【摘要】 石油储层微孔道的纳米减阻技术是一种降低油田注水压力的新技术,其对于确保和提高油田注水量、进而提高低渗油田原油采收率具有十分重要的意义。尽管室内实验和现场试验结果都表明这种技术可以取得显著的减阻效果,但由于内在机制尚不清楚,使得这项技术的发展和应用受到了严重的制约。本文在此背景下,结合微流动方面的研究成果,针对石油储层微孔道结构的特点,提出了基于纳米滑移效应的减阻机理,并对其进行了较系统的实验验证。具体工作包括:1)提出了以纳米滑移效应为核心的石油储层微孔道纳米减阻机理。纳米颗粒与水分子发生竞争吸附,取代水化层在储层微孔道壁面形成强吸附层。该吸附层具有纳米结构和超疏水特性,当水流从纳米层表面流过时,产生了纳米滑移效应,使流道的有效直径超过实际直径,从而使流量提高、流动阻力下降。2)根据滑移长度的定义和多孔介质的基本渗流定律,建立了纳米颗粒吸附多孔介质的水流滑移模型,给出了滑移长度和渗透率之间的数学关系。该模型将宏观效应和微观特征联系起来,为纳米减阻机理提供了理论依据。3)基于对储层微孔道特性和纳米颗粒表面特性的研究结果,分析了疏水纳米颗粒在地层微孔道中的微观受力特征,归纳和推导了纳米颗粒与孔壁的各种微观作用能公式,并进行了数值计算。计算结果表明,静电引力作用是纳米颗粒克服疏水阻力作用的主要因素,多氢键作用是颗粒牢固吸附在储层微孔道壁面的关键。这一结果为纳米颗粒取代水化层形成纳米颗粒强吸附层提供了理论依据。4)采用岩心吸附和SEM扫描相结合的方法,观测了纳米颗粒在岩心表面的吸附特征和分布状态。结果表明,纳米SiO₂颗粒比TiO₂、ZnO颗粒与岩石表面的吸附力更强;颗粒在岩心表面的吸附特征受水膜的影响较小,但储层微孔道壁面的粗糙度对吸附特征有较大影响,粗糙度越大,纳米颗粒吸附层的厚度越大。5)利用岩心吸附法和纳米粉体压片法构建了微纳米结构表面,测试了这些表面的接触角和滚动角,采用SEM观测了表面的微观结构。结果表明,这些表面具有微纳米复合结构,其润湿性由强亲水变为超疏水,这说明疏水纳米颗粒的吸附使岩石表面具有了超疏水特性。通过数值计算分析了影响发生去水湿现象的一些规律,揭示了岩石润湿性变化的机制。6)基于纳米滑移效应的减阻机理开发了多种纳米增注剂样品,通过岩心流动实验评价了这些样品的减阻效果。结果表明,2种修饰剂改性的纳米SiO₂和两种粒径的ShU2样品均具有明显的减阻效果,水相渗透率平均增幅达24%～59%。7)模拟地层温度和压力条件,通过岩心流动实验对不同预处理工艺、以及纳米液注入量、纳米液浓度和关井时间等参数进行了优化,确定了矿场试验技术参数,制定了选井原则。设计了3口井的试验方案,开展了2口注水井的纳米减阻矿场试验。试验结果显示,保持注水量不变,注水压力平均降幅为4～12.5MPa。8)在模拟纳米颗粒吸附毛细管内水的流动特性的基础上,采用LBM模拟了纳米液驱替岩心流动实验结果,反演了纳米颗粒吸附引起的实验岩心微孔道壁面的滑移长度。更多还原

【Abstract】 Drag reduction by hydrophobic nanoparticles （HNPs） is a new technology to enhance water injection or decrease injection pressure in reservoir micro-porous tube. It is of great importance to enhance water injection and then to improve oil recovery for low permeability reservoir. Although results from laboratory and field tests have showed that significant drag reduction could be achieved through this technology, the development and application of the technology is severely constrained because of its unclear mechanism. A drag reduction mechanism based on slip effect on nano-structural interface is proposed according to the characters of porous structure in reservoir and validated by a series of experiments. Specific tasks and their accomplishments are given below.1) Based on slip effect on nano-structural interface, a drag reduction mechanism is proposed. After HNPs are poured into formation, emulative adsorption appears between HNPs and water molecules, then HNPs are adsorbed on porous walls and hydrophobic nanoparticles layers （HNPLs） are formed to replace hydrated film. These layers have both micro- and nano-structures’ and superhydrophobic properties, and when a driving pressure is applied to the water stream, the slip effect takes place in reservoir microchannels, which leads to larger effective diameter. As a result, the flow rate increases and the flow resistance is greatly reduced.2) According to the definition of slip length and basic fluid dynamics law in the porous medium, a slippage model of uniform porous media is introduced with HNPs-adsorbed boundary, and the relative formulas between slip length and permeability is derived. This model combines macroscopical effect with microscopical features , provides a theoretical guidance and makes a good interpretation to the drag reduction mechanism of HNPs.3) Based on the characteristics of the porous structure of reservoirs and the surface characteristics of HNPs, microcosmic force analysis of HNPs in reservoir microchannels is performed, and some formulas are deducted to calculate the relative microscopic interaction energy of HNPs with porous walls. The results show the electrostatic attraction is the main factor for HNPs to overcome resistance force, and multi Hydrogen bonding attraction is a key role for HNPs to adsorb firmly on rock porous walls, which can provide a theoretical explaination for HNPLs to be formed instead of hydrated film on porous walls in reservoir.4) core adsorbing HNPs method and observation method by Scanning Electron Microscope （SEM） , are used to study the adsorption character and distribution state of HNPs on core surfaces. The results show that the adsorptive power of HNPs SiO₂ is stronger than that of HNPs TiO₂ or ZnO on core surfaces, furthermore the influence of the hydrated film on absorption character is of lesser significance than that of the influence of surface roughness of microporous walls. With walls of increasing roughness, the HNPs-adsorbed layers increase in thickness correspondingly.5) Both core adsorbing HNPs method and pressed slice with nanoparticles method are adopted to construct micro- and nano-structural surfaces with HNPs directly. The contact angles and rolling angles of water drops on these surfaces are tested, and SEM or FESEM is used to observe the microstructure of them. The results show that these surfaces are irregular micro- and nano-structural, air-solid compound interfaces and their wettability is changed from strong hydrophobic to superhydrophobic. It suggests that the adsorption of HNPs changes the wettability of core surfaces from hydrophobic to superhydrophobic. Some rules impacting on dewetting phenomenon are studied and the mechanism of wettability change are revealed on the core surface by numerical calculation.6) Several samples of injection-argumented HNPs are developed based on the drag reduction mechanism proposed in this paper, and core displacement experiments are used to evaluated drag-reducing effect. The results show that the drag-reducing effect of these samples is evident, which are the HNPs SiO₂ modified by two kinds of hydrophobic material and the one, named ShU2, with two kinds of diameter, and the water-phase effective permeability of cores is increased by 24%～59%.7) Core displacement experiments are conducted to determine a pretreatment technique, and to optimize injection volume of HNPs fluid, concentration of HNPs, shut-in time and other parameters under the conditions of reservoir temperature and pressure. Based on the experimental results, the principles to choose the well for filed trial are established, and the technical parameters of filed trial are optimized. Trial projects of three wells were designed, and filed trials of two wells were implemented. The results showed that the injection pressure decrease by 4 to 12.5 MPa while previous water injection rate is maintained.8) Based on the successful simulation of water flow through the HNPs-adsorbed capillary, Lattice Boltzmann method is introduced to simulate the results of HNPs-adsorbed core displacement experiment, and then slip length was deduced on the microporous walls of HNPs-adsorbed core samples.更多还原