三次采油与提高原油采收率(2/4): 毛细管力与界面张力的残余油捕集

第二部分：毛细管力与界面张力的残余油捕集

Part 2: Residual Oil Trapping by Capillary Forces and Interfacial Tension

承接前文，当二次采油的红利逐渐消退，油田开发在物理与认知两个层面同时遇到了瓶颈。在本部分，我们将聚焦于探讨文章核心主题所面临的关键挑战：为什么常规水驱无法采出所有的原油？微观世界中的毛细管力和界面张力是如何共同构成难以逾越的物理屏障的？同时，我们也将剖析这些物理挑战如何引发了整个石油行业的集体焦虑，即著名的“石油峰值”理论带来的认知震荡。

Continuing from the previous text, as the dividends of secondary recovery gradually fade, oilfield development runs into limits on both the physical and the cognitive side. In this section, we will focus on exploring the key challenges related to the article's central themes: Why can't conventional waterflooding extract all the crude oil? How do capillary forces and interfacial tension in the microscopic world combine to form a barrier that is difficult to overcome? Simultaneously, we will analyse how these physical challenges triggered collective anxiety across the petroleum industry, namely the cognitive shock brought about by the famous "Peak Oil" theory.

在二次采油的中后期，油田往往会陷入低效的“水中捞油”境地。这种现象的流体力学根源在于水和原油之间的流度比（Mobility Ratio）差异以及岩石地层的强烈非均质性。由于水的黏度通常远低于原油，注入的水在岩石孔隙中优先流向低阻力路径，容易发生“粘性指进（Viscous Fingering）”现象。注入水会沿着渗透率高、阻力最小的大孔道迅速窜流至生产井，导致大孔道被冲洗干净，而大量滞留于微细缝隙和低渗区域的原油基本未被动用。随着时间的推移，采出液的含水率不断升高。以部分老油田为例，综合含水率甚至会高达 95% 以上，带来可观的水循环处理成本。

In the middle-to-late stages of Secondary Oil Recovery, oilfields often fall into an inefficient regime of "fishing for oil in water." The fluid mechanical root of this phenomenon lies in the difference in the Mobility Ratio between water and crude oil, as well as the strong heterogeneity of the rock formation. Because the viscosity of water is typically much lower than that of crude oil, the injected water preferentially follows the path of least resistance through the rock pores, making it prone to the phenomenon of "Viscous Fingering". The injected water rapidly channels through large pore channels with high permeability and minimum resistance straight to the production wells, leaving the large channels washed clean while large volumes of crude oil held in micro-fissures and low-permeability areas remain largely unswept. As time passes, the water cut in the produced fluids rises steadily. Taking some mature oilfields as an example, the comprehensive water cut can even exceed 95%, leading to substantial water circulation and treatment costs.

更关键的挑战出现在微观尺度。那些未被水驱波及的原油，被称为“剩余油”或“残余油”，它们以簇状、柱状、膜状或孤立在盲端孔隙中的形式存在。阻碍它们流动的主要物理阻力，是很高的界面张力（Interfacial Tension, IFT）和由其引发的毛细管力。从物理化学角度看，油和水是高度互不相溶的多相流体系统，两者之间存在着约 30 至 50 mN/m 的界面张力。在尺寸仅为微米级的岩石孔喉中，这种张力结合岩石的润湿性，会产生显著的贾敏效应（Jamin Effect）。毛细管阻力将油滴锁固在孔隙内。如果要仅凭物理手段克服这种阻力，所需的宏观注水压力将远远超过地层的破裂压力限值。因此，传统的压力驱替在微观毛细管力面前难以奏效。

An even more decisive challenge appears at the microscopic scale. The volumes of oil bypassed by waterflooding are known as "remaining oil" or "residual oil," and they exist in forms such as clusters, columns, films, or isolated droplets in dead-end pores. The principal physical resistance impeding their flow is the high Interfacial Tension (IFT) and the resulting capillary forces. From a physicochemical perspective, oil and water are highly immiscible multiphase fluid systems, with an interfacial tension of approximately 30 to 50 mN/m between them. In rock pore throats measuring only micrometers in size, this tension, combined with the wettability of the rock, generates a significant Jamin Effect. Capillary resistance holds the oil droplets within the pores. To overcome this resistance relying solely on physical methods, the required macroscopic water injection pressure would far exceed the fracture pressure limit of the formation. Therefore, traditional pressure displacement is ineffective against microscopic capillary forces.

伴随着物理开发瓶颈的凸显，整个石油工业在 20 世纪下半叶遭遇了严重的心理危机。随着开采难度的增加和旧油田产量的递减，由地质学家M. King Hubbert提出的“石油峰值（Peak Oil）”理论开始在学术界和工业界广泛传播。该理论预测，石油产量将遵循钟形曲线，在达到峰值后不可逆转地走向资源枯竭。1973 年和 1979 年的两次石油危机进一步加剧了这种忧虑，带来了全球性的能源短缺焦虑和经济动荡。在心理学上，这种对资源匮乏的恐慌引发了行业的集体“认知失调（Cognitive Dissonance）”。从业者一方面深知现代文明的运转离不开化石能源，另一方面也认识到传统的水驱技术已接近其能力上限。

Accompanying the prominence of physical development bottlenecks, the entire petroleum industry encountered a severe psychological crisis in the second half of the 20th century. With increasing extraction difficulties and declining production from old oilfields, the "Peak Oil" theory, proposed by geologist M. King Hubbert, began to spread widely through academia and industry. This theory predicted that oil production would follow a bell-shaped curve and irreversibly decline toward resource depletion after reaching a peak. The two oil crises of 1973 and 1979 further deepened this concern, leading to global energy shortage anxiety and economic turbulence. Psychologically, this panic over resource scarcity triggered a collective "Cognitive Dissonance" within the industry. On one hand, practitioners knew well that the operation of modern civilization could not be separated from fossil fuels; on the other hand, they recognised that traditional waterflooding technologies had reached the limit of what they could deliver.

这种忧虑与认知失调，最终成为打破旧有范式的催化剂。石油工程师和决策者意识到，为了突破增长的极限，必须经历一次深刻的“思维模式转变（Mindset Shift）”。行业必须摒弃单纯依赖“发现（Discovery）”新储量的路径依赖，转而拥抱依靠技术“创新”来提高现有油藏“采收率（Recovery）”的科学思维。人类认识到，真正的稀缺并非地质资源的枯竭，而是开采技术的局限。

This concern and cognitive dissonance ultimately became the catalyst for breaking the old paradigm. Petroleum engineers and policymakers realized that to break through the limits to growth, they must undergo a profound "Mindset Shift". The industry had to abandon its exclusive reliance on the "Discovery" of new reserves, and instead embrace the scientific thinking of relying on technological "innovation" to improve the "Recovery" of existing reservoirs. Humanity recognized that true scarcity was not the depletion of geological resources, but the limitations of extraction technology.

下期预告：既然宏观的压力驱替难以奏效，出路就在于向微观尺度推进，利用热力学和物理化学手段从分子层面瓦解阻力。这就要求我们必须找到能够大幅降低界面张力的化学药剂，以及能够精确测量这些微小张力变化的专用仪器。在接下来的部分中，我们将介绍这一技术路线的核心机制及其关键测量工具。

Next: Since macroscopic pressure displacement could not work, the way forward was to move to the microscopic scale, utilizing thermodynamic and physicochemical means to dismantle the resistance at the molecular level. This required chemical agents capable of drastically reducing interfacial tension, as well as dedicated instruments capable of precisely measuring these minute tension changes. In the next section, we will set out the core mechanisms of this technical route and its key measurement tools.