Foam Improved Oil Recovery: Effects of Flow Reversal

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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.