多孔介质中乳状液微尺度变形对水驱后残余油作用机理研究

Emulsion has the characteristics of high viscosity and strong mobility control, the high permeability layers can be plugged by the large particle size emulsion droplets to enlarge the swept volume, the technology of using emulsion flooding to improve oil recovery has important application value in the field of petroleum engineering. The emulsion droplets with different particle size will be formed in the process of Emulsion flooding, those large size emulsion droplets will deform when they pass through the pore throat due to their viscoelasticity, while the small particle size emulsion droplets can pass the pore throat easily with almost no deformation. Most of the current researches on the oil displacement mechanism of the emulsion are based on traditional theory of capillary number and regard the emulsion as continuous phase, without considering the viscoelasticity and micro force of emulsion. This project researchs the emulsion effect on five kinds of residual oil after water flooding(namely oil drop, oil column, oil film, the oil in dead end pores, cluster-type oil), and in this project the emulsion is regarded as a dispersion phase and the emulsion droplet is regarded as research object, considering the viscoelasticity, the mathematical model of above five kinds of residual oil is built to calculate the micro-force of emulsion displacement, the residual oil displacement mechanism of the emulsion under the pore throat level is researched by the combination of the experiment and theory, and the action mechanism of expanding swept volume and improving oil displacement efficiency of the emulsion is also researched through the core displacement experiments. Finally, a more clear understanding on the displacement mechanism of emulsion can be presented through the study of this project.

乳状液具有粘度高，流度控制强的特点，粒径大的乳状液滴能够封堵高渗透层，起到扩大波及体积的作用，乳状液驱油提高采收率技术在石油工程领域具有重要的应用价值。乳状液驱油过程中，在微观孔道里会形成粒径尺寸大小不一的乳状液滴，粒径大的乳状液滴存在粘弹性，在孔喉中运移存在变形，而小粒径的乳状液滴几乎不存在变形，很容易通过孔喉。目前在乳状液驱油机理研究方面，都是基于传统毛管数理论展开的，将乳状液作为连续相，研究缺陷是没有考虑乳状液的粘弹性和微观力。本课题将乳状液作为分散相，以乳状液滴为研究对象，研究乳状液对水驱后五种残余油（油滴、油柱、油膜、盲端油、簇状油）的作用，考虑粘弹性，建立乳状液驱替五种残余油的数学模型，计算乳状液驱替的微观力，实验和理论相结合研究孔喉级别乳状液滴的驱油机理；并通过岩心驱替实验，研究乳状液驱扩大波及体积和提高驱油效率的作用机理。本研究能够对乳状液的驱替机理有一个更加清晰的认识。

化学驱提高采收率技术在我国取得了较好的效果，但仍然存在一些问题。聚合物没有突破高矿化度、高温条件的限制，这就限制了聚合物驱的推广，表面活性剂驱可以达到耐高温、高矿化度的要求，但不能实现流度控制，容易形成窜流，乳状液在油藏中运移具有较高的粘度，可以达到控制流度，扩大波及体积的作用，又具有弹性和降低油水界面张力的作用，可以达到提高驱替效率的作用，成为化学驱的一个新的研究方向。目前，国内外对乳状液微观驱油机理研究很薄弱，没有研究孔喉级别乳状液滴的驱替机理，关于乳状液驱油机理的研究多数基于传统的毛管数理论进行的，没有考虑到乳状液粘弹性变形和微观力。.本项目从孔喉级别单个乳状液驱替水驱后残余油的微观驱油实验出发，从粘弹性和微观力方面建立乳状液驱替残余油的数学模型，实验和理论相结合研究孔喉级别乳状液的驱油机理，通过均质岩石和纵向非均质岩石驱替实验，研究乳状液扩大波及体积和提高驱油效率的作用。研究表明，应用复合乳化剂体系，当浓度为0.4~0.5wt%、乳化剂溶液注入速度0.3 ~0.4mL/min时，能够形成稳定性较好的孔喉级别乳状液，形成的乳状液粘度能够达到40~70，具有较强的粘弹性。孔喉级别乳状液滴能使水驱后的油膜、油滴、油柱和盲端残余油启动、向前运移，孔喉级别乳状液滴在喉道中运移接触到残余油后，要发生变形，在变形的相反方向产生微观的法向应力，这将作用于残余油上，它是驱替残余油的微观驱动力，孔喉级别乳状液滴的微观力远远大于水驱宏观压力，因此能够使残余油启动。乳状液的粘弹性对采收率的贡献在10%左右，比聚合物驱提高采收率5%左右，在高温、高矿化度条件下，乳状液驱的驱油效果更好，更加适合于高温高矿化度油藏。.本研究进一步明确了乳状液的驱油机理，完善了化学驱的方法，对于矿场中化学剂的选择具有重要指导意义，为高温高矿化度油藏条件下，高含水后期进一步开发提供可行性方法。