Reclamation of polluted sites

Capillarity

Capillarity controls the penetration of immiscible fluids in porous media. It occurs in the unsaturated zone. From the water table going down, the pressure increases. The smaller the tube, the higher the rise and attraction. Above the water table, inside the capillarity tube, there is a negative pressure. Around the domain and also inside the tube where there is no water, there is atmospheric pressure. In the tube, there is a different value of pressure. →YOUNG – LAPLACE Balance of forces. The force that is rising, keeping the interface above the water table, is equal to the pressure difference multiplied by the area.

There is a coarse material at the bottom of the tube to prevent capillary rise.

The forces acting at the interface between the various phases are a result of molecular actions and are called capillary forces. One of the characteristic properties of every fluid is its surface tension, defined as "the force acting on a liquid surface that results in a minimum liquid surface area. The term

Surface tension, that expresses the tendency of a fluid to reduce the contact area, is generally used only for liquids in contact with air. When there are separation surfaces between two or more liquids, or between liquid and solid, the term interfacial tension, σ, is used.

Capillary pressure, pc, is defined as the pressure difference at the interface between two immiscible fluids: in particular, it is the pressure difference measured between the non-wetting, pnw, and the wetting phase, pw.

Capillary pressure curves = for different soils layers they represent the relationship between the capillarity rise (level of water in cm) and the saturation. From the water table where there is capillarity equal to zero to the top, (under steady state condition and in equilibrium condition where there is a decrease of the capillarity pressure from the bottom to the top), distribution of the saturation at each depth depending on the characteristic of the soil. The heterogeneity and fine material has a more slopy curve.

The change of saturation is faster than the other material. Close to 1, there is the height of the capillarity fringe. Pressure to be applied (capillary pressure) in order to inject a certain amount of air to displace the water in the porous medium - another interpretation of the graph. We can determine the curve in the lab using a particular apparatus. At the beginning, a wet sample is placed in the core inside a non-wetted fluid. Then, the pressure of the non-wetting fluid is increased in order to displace the fluid related to the pores, making it possible to determine the saturation. This process is a successive states of hydrostatic equilibrium and it's possible to obtain a drainage curve (wetting fluid is displaced by non-wetting) or the opposite, the imbibition curve (wetting fluid displaces the non-wetting one), in which there is a decrease in capillary pressure until the complete saturation of the sample. The maximum removal of the oil inside the pores is the final point of the imbibition.

The main curve are limited by the minimum saturation of water and oil and they represent two limits in which there are at least two fluid inside the pores. Initially the sample is saturated only by water on the right and on the left only saturated by oil (NON WETTING FLUID) from the top. From the top we start injecting water until the final point and then we can decrease the water pressure arriving at the top again. If we have a water wet soil we start from the displacement pressure point.

13Leverett model is useful to normalized this curve. →Brooks and Corey model Linearized the curve in a semilogarithmic curve using effective saturation and normalized capillarity pressure bubbling point (hb) =min pressure to applied to start create bubble. →Van Genuchten model is smoother. Alfa is 1/hb and m and n are similar to lambda in the other model. →Shark Finn model 3 phases (oil red, water greed, air white), pc is the capillarity pressure. More realistic model of the representation.

of the saturation problem in 3D situation.

One piezometer far away to the contaminated source, second piezometer in the source of the contamination there are two interface (air-oil and water-oil). Water is always the wetting phase. Under equilibrium condition we have the distribution of the capillar pressure which is linear with the depth. The condition of the aquifer system, out of the piezometer, in the interface (water-oil) the pressure is zero capillary pressure and the pressure in the two liquid is the same. Moving inside the water pressure evolving based on the density. Between the 2 fluid there is capilar pressure that induce a variation of saturation. In the aquifer system we don't have a fully saturation of the LNAPL but there is a variable concentration below the interface water-oil. Above the interface oil-air, we don't have a 2 phase system but 3 phase system (add air), the capilar pressure between the air and the oil is almost the distance (Pc,ao in the graph). Neglect

The density of air. Composition of the capilar pressure between oil-water and the capilar pressure between the air-oil create the shark finn. The area tratteggiata in the graph a dx can't be recovered. In a general way higher thickness in well, higher capillarity pressure and higher LNAPL saturation.➔ Per eliminare LNAPL, dosare tensioattivi per renderlo più mobile, cambiare la viscosità diminuendola14 Permeability is the same in water or oil system, so I can find a relationship between the two conductivity. RHOr is the ration between the density of oil and water, same for Mur. Viscosity of oil is much higher than the water and the density of the oil is lightly lower than the density of the water. The K of water is much higher than the conductivity of the oil in saturation condition Relative permeability (is a function of the saturation of the fluid) is defined as the ratio of the effective permeability of a particular fluid and the absolute permeability of the

Medium where flow is occurring. When are present 2 fluid the relative permeability is lower than 1, so there is an impairment of the permeability. If more than one fluid is present, for each fluid a different value of effective permeability is found, which is lower than the intrinsic permeability and depends on the saturation of the fluid. The sum of the effective permeabilities is always lower than the absolute permeability (local lack of phase continuity).

At high level of the saturation correspond high value of conductivity for the wetting phase, and if we decrease the saturation we see a decrease of the conductivity as well.

The average value of the relative conductivity is calculated integrating the green curve between the two high and dividing for the total thickness, this calculation provide info about the speed that we can recover the oil, because if average k is very low means that it will take a long time to recover all the oil.

In saturated condition q is the specific flow rate.

The column is horizontal so there is no gradient in elevation (z=0). q is a function of permeability and viscosity. Two fluids are present and we want to calculate the Darcy velocity of one fluid. The porous medium is saturated both where Q1 passes and where Q2 passes, so we can apply Darcy's law. There is a different pressure between the two fluids and we relate the two fluids with their relative permeability. We imagine separating the two fluids so they cannot mix, but they pass through A1 and A2. We can rewrite q using the partial surface areas A1 and A2. In A1, we have full saturation of the first fluid, so we can write the relationship as shown above, where A1/A is proportional to the saturation. Therefore, there is a linear relationship between the saturation and the relative permeability, as shown in the graph. This is the simplest model in multiphase flow. There is no movement of fluid in the residual phase because when there is a continuous phase, applying pressure can displace the fluid. However, when we have a discontinuous phase,

phase we can't apply a pressure differentto move the different phase.

3. High resolution characterization of contaminated aquifer system

Over time there is a solubilization of the contaminant, over the decades there is the decay of thecontaminant. There is also a transport of the contaminant in the solid phase due to the diffusion. In the endarrive to the rock matrix that become the source of contamination.

The heterogeneity of the aquifer system is important to take into account and also the distribution of thehydraulic conductivity because the low conductivity zone plays an important role. This leads to the tailingand to long term for the recovery.

We have to characterize the field of motion for the characterization of the hydraulic of the system taking intoaccount:

• Hydraulic typology
• Specific storage 16
• Hydraulic conductivity
• Gradient

But also the characterization of the contamination with the determination of the distribution of thecontaminant in al the phases.

➔ High

The resolution is high due to the conductivity and concentration.

3.1 Determine the hydraulic conductivity

Use sophisticated tools and equipment for this purpose.

Classical methods for determining hydraulic conductivity include the reconstruction of stratigraphy and laboratory analysis such as particle size distribution and granulometric analysis.

A slug test is a single-well groundwater test where the static level in a well or piezometer is instantaneously varied, and the recovery of the original level is measured over time. Interpretation methods for this test include Bower-Rice, Cooper, KGS, and Papadopulus. Inside the well, a tool is used to determine hydraulic conductivity, electrical conductivity, and the distribution of contaminants.

A high-resolution slug test can be performed using a pneumatic slug test at different depths in the aquifer system. Air is injected and released, and the hydraulic conductivity is determined at each depth. This process can be repeated at higher depths to determine the hydraulic conductivity.

We can...

determine the K using the electrical conductivity in situ and the grain size distribution; with these 2 parameters we can estimate K. The prof has a quadrupole that is injecting current in two electrodes and then measure the voltage in other two electrodes. The electrical conductivity is directly determined along the depth. A higher value of electrical conductivity is related to the presence of clay.

HPT = hydraulic profile tool is a system where we have a rod and a small aperture where we can inject water, we can measure discharge rate and the injection pressure. We have to relate these parameters with the K using Darcy's law. It is less precise than the sludge test but the measurements are made immediately.

Characteristics of the injection tool:

• Pressure: 0/6 atm
• Q: 0/1 l/min

Pressure is higher where we have higher electrical conductivity and it is an indicator of a finer material. In the background, pressure is increasing linearly, which means the presence of a saturated zone.

There are two approaches