Displacing fluid

Chemical techniques change the physical properties of either the displacing fluid, or of the oil, and comprise of polymer flooding and surfactant flooding. 

Polymer flooding alms at reducing the amount of by-passed oil by increasing the viscosity of the displacing fluid, say water, and thereby improving the mobility ratio (M). 

Miscible processes are aimed at recovering oil which would normally be left behind as residual oil, by using a displacing fluid which actually mixes with the oil. Because the miscible drive fluid is usually more mobile than oil, it tends to bypass the oil giving rise to a low macroscopic sweep efficiency. The method is therefore best suited to high dip reservoirs. Typical miscible drive fluids include hydrocarbon solvents, hydrocarbon gases, carbon dioxide and nitrogen. 

However, ia some cases, the answer is not clear. A variety of factors need to be taken iato consideration before a clear choice emerges. Eor example, UOP s Molex and IsoSiv processes are used to separate normal paraffins from non-normals and aromatics ia feedstocks containing C —C2Q hydrocarbons, and both processes use molecular sieve adsorbents. However, Molex operates ia simulated moving-bed mode ia Hquid phase, and IsoSiv operates ia gas phase, with temperature swiag desorption by a displacement fluid. The foUowiag comparison of UOP s Molex and IsoSiv processes iadicates some of the primary factors that are often used ia decision making ... 

Chemical processes work either to change the mobility of a displacing fluid like water, or to reduce the capillary trapping of oil in the rock matrix pores. Reducing the mobility of water, for example by adding polymers, helps to prevent fingering, in which the less viscous water bypasses the oil and... 

A recent application of this type of fluid is assistance in the removal of ingested salt spray from jet aircraft compressors and the neutralisation of corrosive effects. Other types of water-displacing fluids are claimed to have fingerprint neutralising properties or to be suitable for use on electrical equipment. Some oil-type materials serve temporarily as engine lubricants and contain suitable inhibitors to combat the corrosive products of combustion encountered in gasoline engines. 

The foam, having a viscosity greater than the displacing medium, will preferentially accumulate in the well-swept and/or higher permeability zones of the formation. The displacing medium is thus forced to move into the unswept or underswept areas of the formation. It is from these latter areas that the additional oil is recovered. However, when a foam is used to fill a low oil content area of the reservoir, the oil contained therein is, for all practical purposes, lost. This is because the foam functions to divert the displacement fluid from such areas [1574-1576]. 

The principal experimental method used to measure the density of a solid is determination of the mass of liquid displaced by a known mass of solid. It is essential that the solid have no appreciable solubility in the liquid, that all occluded air be removed from the solid and that the density of the displacement fluid be less than that of the solid lest the solid float. Densities of crystalline solids also can be determined from the dimensions of the unit cell. Davis and Koch discuss other methods for measuring the density of liquids and solids such as hydrostatic weighing of a buoy and flotation methods. 

Hot water injection via injection wells heats the soil and groundwater and enhances contaminant release. Hot water injection also displaces fluids (including LNAPL and DNAPL free product) and decreases contaminant viscosity in the subsurface to accelerate remediation through enhanced recovery. 

The displacing fluid may be steam, supercritical carbon dioxide, hydrocarbon miscible gases, nitrogen or solutions of surfactants or polymers instead of water. The VSE increases with lower mobility ratio values (253). A mobility ratio of 1.0 is considered optimum. The mobility of water is usually high relative to that of oil. Steam and oil-miscible gases such as supercritical carbon dioxide also exhibit even higher mobility ratios and consequent low volumetric sweep efficiencies. 

As the displacing fluid front advances, the structural complexity of these... 

It is now well established through studies in many laboratories throughout the world that foam injection shows considerable promise as an agent for the improvement of oil recovery from watered-out. porous media, and for the diversion of the flow of other oil-displacing fluids from more permeable paths into less permeable paths in the medium<1). Whilst the reasons for the effectiveness of foam for these purposes are not. completely clear, the explanation is thought to lie in the behaviour of the foam lamellae... 

Enhanced oil recovery processes involving displacing fluids such as dense C02 and liquified petroleum gases (LPG) are currently being applied in different parts of the world. At moderately high pressure and reasonable temperatures common in many reservoirs,... 

Many engineering operations involve the separation of solid particles from fluids, in which the motion of the particles is a result of a gravitational (or other potential) force. To illustrate this, consider a spherical solid particle with diameter d and density ps, surrounded by a fluid of density p and viscosity /z, which is released and begins to fall (in the x = — z direction) under the influence of gravity. A momentum balance on the particle is simply T,FX = max, where the forces include gravity acting on the solid (T g), the buoyant force due to the fluid (Fb), and the drag exerted by the fluid (FD). The inertial term involves the product of the acceleration (ax = dVx/dt) and the mass (m). The mass that is accelerated includes that of the solid (ms) as well as the virtual mass (m() of the fluid that is displaced by the body as it accelerates. It can be shown that the latter is equal to one-half of the total mass of the displaced fluid, i.e., mf = jms(p/ps). Thus the momentum balance becomes... 

The upward velocity of the displaced fluid flowing in the interstices between the particles is significant, so the apparent settling velocity (relative to a fixed point) is significantly lower than the particle velocity relative to the fluid. 

In this equation, V0 is the relative velocity between the unhindered particle and the fluid. However, in a hindered suspension this velocity is increased by the velocity of the displaced fluid, which flows back up through the suspension in the void space between the particles. Thus, if Fs is the (superficial) settling velocity of the suspension (e.g., swarm ) and VL is the velocity of the fluid, the total flux of solids and liquid is relative velocity between the fluid and solids in the swarm is Vr = Vs — VL. If the total net flux is zero (e.g., batch settling in a closed-bottom container with no outflow), elimination of VL gives... 

These are Equations 13.5-13.7, modified to account for the loss of the displaced fluid. 

The force due to the movement of the liquid surrounding the bubble is m (dt>ldt). For a sphere moving in an infinite medium of an inviscid fluid, the mass of the liquid m is equal to half the mass of the displaced liquid. The authors, however, assumed merely a direct proportionality between m and the mass of the displaced fluid, instead of the above relationship, because they considered their flow not to be irrotational. 

Since the fraction of the area available for flow of the displaced fluid is e, its upward velocity is uc( 1 — e)je so that ... 

The final consolidation of the sediment is the slowest part of the process because the displaced fluid has to flow through the small spaces between the particles. As consolidation occurs, the rate falls off because the resistance to the flow of liquid progressively increases. The porosity of the sediment is smallest at the bottom because the compressive force due to the weight of particles is greatest and because the lower portion was formed at an earlier stage in the sedimentation process. The rate of sedimentation during this period is... 

When the particles of two sizes are settling together, the upflow of displaced fluid is caused by the combined effects of the sedimentation of the large and small particles. If this upward velocity is up, the sedimentation rates uml and uMs will be obtained by deducting u F from the velocities relative to the fluid. 

Then, since the volumetric flow of displaced fluid upwards must be equal to the total volumetric flowrate of particles downwards, then ... 

Polymers increase the viscosity of the soil washing fiuids. Increased viscosity provides mobility control, which reduces the fingering of the displacing fiuid past the displaced fluid. It also helps ensure that the contaminated area is efficiently contacted by the soil washing solution. 

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