Foam Improved Oil Recovery: Effects of Flow Reversal

该项目的背景是提高石油采收率。在石油开采作业中，只有一小部分石油能够在储层自身压力下流出储层。在那之后，石油工程师就会向储层注入液体，试图把剩余的油挤出来。泡沫（由分散在水表面活性剂液体中的气泡组成）是实现这一目标的有希望的候选注射流体。由于油气储层很难进入（在地下，而且经常处于恶劣的环境中），通常不可能直接观察到注入的泡沫是如何在其中流动的。因此，有一个水库流动的数学模型是非常有价值的。该项目将开发一个这样的模型，即所谓的“压力驱动增长”模型，该模型的计算效率特别高，因为它只关注泡沫前缘在油藏中传播的过程，而不是整个油藏的状态。尽管计算效率很高，但压力驱动增长模型目前仍有许多局限性。其中一个限制是，该模型目前无法描述泡沫前沿经历方向突然改变的情况。这是一个问题，因为在泡沫提高采收率的过程中，在向给定井注入泡沫一段时间后，已经在储层内的泡沫可能会在邻近的新注入井投产时改变其运动方向。这个项目的目的是调整压力驱动的增长模型来描述这种情况。然而，为了做到这一点，我们首先需要探索另一个模型（即所谓的“分流”理论），它支持压力驱动的增长。事实上，分数流动理论比压力驱动增长理论包含了更细致的细节，它提供了非常具体的信息，可以准确地了解气体和液体在泡沫前沿相遇时发生了什么。这些信息包括气泡前部气体和液体的分布如何变化，气泡前部有多厚，以及它的流动性如何：所有这些信息随后被输入到控制压力驱动增长给出的不太详细描述的参数中。因此，我们的目标是探索分数流动理论如何响应流动方向的变化，并使用分数流动结果来参数化压力驱动的增长。实现这一目标后，我们的目标是在一些涉及流动方向改变的石油工程情况下测试三参数化压力驱动增长模型。该模型的结果还将与石油工程中传统采用的计算更密集的“整个油藏”方法进行比较。受益的主要应用领域当然是石油和天然气，石油和天然气行业正在设法回收更多的流体，从而从现有的油田中获得更多的收入。在某些情况下，例如对于非常成熟的油田，采用泡沫提高采收率甚至可能会决定油田是否需要关闭。通过使用建模工具预测泡沫如何提高石油采收率，石油公司将能够在进行任何昂贵的钻井之前规划和优化作业，从而减少了采用试验和错误方法的需要。虽然该项目的好处主要集中在石油和天然气方面，但也有望带来更广泛的好处。我们将在油藏中研究泡沫前沿的前沿传播模型与控制许多其他系统的模型非常相似，包括固液悬浮力学、空气中的超音速流动、流行病的传播、行人流和火灾前沿传播等。因此，可以从项目中获得对其他系统的新见解。

The context of this project is improved oil recovery.In petroleum extraction operations, only a fraction of the oil managesto flow out of a reservoir under the reservoir's own pressure.After that, petroleum engineers resort to injecting fluids into thereservoir to try to push out remaining oil.Foam (consisting of bubbles of gas dispersed in aqueous surfactantliquid) is a promising candidate injection fluid to achieve that.Because oil and gas reservoirs are difficult to access (beingunderground and often in harsh environments), it is generally notpossible to observe directly how an injected foam flows inside them.Having a mathematical model of the reservoir flow is thereforevery valuable.This project will develop one such model, so called ``pressure-drivengrowth'', which is particularly computationally efficient, as itfocusses just on a foam front as it propagates through the reservoir,rather than on the state of the entire reservoir away from the front.Despite its computational efficiency, the pressure-driven growth modelcurrently has a number of limitations.One such limitation is that the model is not currently able todescribe a situation in which the foam front undergoes a sudden changein direction.This is an issue since, during foam improved oil recovery, foam thatis already within the reservoir after a period of foam injection intoa given well, may change its direction of motion if a new adjacentinjection well is brought online.The purpose of this project is to adapt the pressure-driven growthmodel to describe situations such as this.However in order to do this, we need first to explore another model(namely so called ``fractional flow'' theory) which underpinspressure-driven growth.Fractional flow theory actually contains a finer level of detail thanpressure-driven growth does, providing very specific information aboutexactly what is happening at a foam front at which gas and liquidmeet.Such information includes how gas and liquid fraction profiles varyacross the foam front, how thick the front is, and how mobile it is:all this information then feeds into parameters governing the lessdetailed description given by pressure-driven growth.Our aim therefore is to explore how fractional flow theory responds tochanges in flow directions, and to use the fractional flow results tore-parameterise pressure-driven growth.Having achieved this, our objective will be to test there-parameterised pressure-driven growth model in a number of petroleumengineering situations that involve flow direction changes.Results from the model will also be compared against a much morecomputationally intensive ``entire reservoir'' approach, which isconventionally employed in petroleum engineering.The main application area that will benefit is of course oil and gas,with the oil and gas industry managing to recover more fluids andhence generate more revenue from existing sites.In certain cases, e.g. for very mature oil fields, employing foamimproved oil recovery might even make the difference between keeping afield open or needing to shut it down.By using modelling tools predicting how foam improved oil recoveryproceeds, oil companies will be able to plan and optimise operations,prior to performing any costly drilling, thereby limiting the need toresort to trial and error approaches.Although benefits of the project focus mostly on oil and gas, widerbenefits are also anticipated.The front propagation models that we will study for foam fronts in oilreservoirs are remarkably similar to models governing a number ofother systems, including mechanics of solid-liquid suspensions,supersonic flow through air, spread of epidemics, pedestrian flow andfire front propagation, amongst others.New insights into other systems such as these can therefore derivefrom the project.