Studying the Transmission Behavior of Two-Phase Flow Oil-Water Mixing Using a Laboratory Multiple Porous Media Model

The formation and flow of emulsions in porous media are common to all technologies used to extract or process oil. In most cases, oil and water emulsions are formed in a porous medium due to oil spills near watery areas or soils containing water. This emulsion leads to a reaction between oil and water, which finds its way to the porous medium. The detailed flow mechanisms of emulsions through porous media are not well understood. In this study, the soil’s oil percentage variation was studied when sand was introduced or an emulsion, i.e., mixed with water, and two porous media, different in composition and physical properties, were used to find out their effect on oil transmission. The percentage of oil and water was calculated at several points at different distances and times. It was noted that the results differed in both mediums due to the difference in permeability, porosity, arrangement of soil particles, compaction process, and other physical properties. Liquids’ viscosity, density, and chemical composition clearly and significantly affect the results. The time for the oil to reach the last point in the pipe differed for both soils. If the time period in the experiment of pumping oil only in sandy soil took 6 hours and the washing process took 3 hours. In organic soil, the time period for the pollutant pumping stage took about 7 hours and the washing stage about 4 hours because the oil is transmitted in sandy soil is faster, but in the experiment of pumping oil and water together, the time period in the process of pumping oil and water together in sandy soil took 4 hours and the washing process 3 hours In organic soil, the period of pumping oil and water together took 5 hours, and the washing period 3 hours, because the percentage of oil was less than in the experiment of pumping oil only. In the soil, that is, if the period of pumping the pollutant increased for more than 15 hours, the oil may reach a distance of more than 4 meters in the soil. As for the washing process, when the oil is mixed with water, it gives better results when washing it than if the oil enters alone into the soil because the proportions of oil when it enters the soil together with the water, it is little and does not rise much, so it is easy to wash.


Introduction
Today, hydrocarbons are the most common kind of energy production.In 2020, annual oil output was expected to exceed 4 billion tons, with an additional 8 million tons of crude oil penetrating the soil and water environment as pollutants.Soil and water contamination is mostly caused by oil.Plants and animals, particularly those that live in coastal areas, suffer from oil pollution.In coastal places, it causes an increase in erosion of the fringe habitats of swamps, which in turn disrupts the cycle of nutrients and water filtration and other regulatory activities of swamps, wreaking havoc on ecosystems [1].As a nonaqueous liquid (NAPL), seeping oil has a complex composition, poor solubility in water, strong binding properties to soil organic matter, and effective anti-sorption properties [2].Heavy metals have a negative impact on the soil's ecological environment because they obstruct the soil's porous structure and change its mechanical composition, compaction degree, structural state, concentration, and content of soil minerals.The chemical constitution of the pollutant and the nature of the soil play significant roles in determining the level of oil contamination in the soil.The vertical sinking of oil tanks or breaks in existing pipes on the oily ground can result from excessive oil contamination.[3] Accidental spillage of oil products on the ground seeps through pores in the soil and groundwater table.Sand and soil contaminated with oil leak out, and oil is in the pores.This decreases the angle of internal friction and weakens the shear force.The initial viscosity of the oil and its saturation level determine hydraulic conductivity.With increased oil content and decreasing pore size, the permeability of oilcontaminated soils declines [4].In loose sand, as opposed to packed sand, the consequences of oil contamination are more pronounced [5].Oil-contaminated soils' limiting dry density, frictional resistance, and compressive strength all decrease as the oil content rises [6].There is strong evidence that oil in the pore fluid significantly impacts the behavior of clay-reactive soil particles [7].According to the literature, oil deposited on clay particles reduces soil shear strength and dry density [8].The subterranean layer of soil is usually divided into two separate zones: an unsaturated zone (aeration zone) and a saturated area.Two forces, gravity, and capillary pressure work on oil as it percolates through unsaturated soil.The free-phase oil would fall to the water table under gravity.The permeability of oil is poor in the saturated zone.Complex lateral diffusion occurs when oil enters this zone and spreads outward from the water table.The water table's gradient parallels the direction of flow.The nature of oil flow is influenced by how oil penetrates the soil, how much of it drains out, how steep the gradient is, how porous the medium is, and how high or low the water table is.When the oil flow in the free discharge area is depleted, the oil in the unsaturated zone is drained until, for all practical reasons, a minimal quantity of oil remains in the unsaturated soil.Variables like soil type and variability in the porous medium determine this minimal volume, also known as residual saturation.During residual saturation, the oil in the core pores exists as a separate volume from the oil in the surrounding pores.The oil is in an inefficient, intermittent phase here.In porous, unsaturated media, certain oils deteriorate.Existing water in the soil is absorbed on the particles' surfaces and evaporates into the pore space [9].An essential feature in oil recovery processes is the movement of emulsions via porous media.In particular, the oil sector relies on it for a variety of industrial and scientific purposes [10][11][12][13][14].Some researchers have hypothesized that oil migrates through reservoir sands as thin oil-in-water emulsions and that oil puddles form when oil reaches fine-grained rocks like silt or shale [15][16][17].The mechanisms by which emulsions migrate over porous media have been the subject of numerous models described in the literature.One of these models [18] looked at how oil droplets move as they travel through porous media, and the results provided insight into how oil droplets flow when they settle into pores smaller than the droplets themselves [19].Different wettability conditions lead to different fluid compositions within the pore space under equilibrium.For example, under wet conditions, water is present around the grains, oil is present in the middle of the pores, and the opposite occurs in the case of wet oil [19].During the flow of O/W emulsions, it is claimed that the permeability of the porous media monotonically decreases with time.It has been found that with increasing water saturation, the relative permeability of the oily phase decreases and the relative permeability of the water phase increases until it reaches residual saturation with oil when the oily phase is immobile.At that point, the oil's permeability varies [20].Experiments have also shown a relationship between temperature and the relative permeability of oil and water in the soil layers.Data were collected at temperatures ranging from 10 °C to 275 °C to show correlations to predict the relative properties of an oil, water permeability, and oil saturation.It was observed that when the temperature increased, the oil saturation decreased while the water saturation increased.At temperatures below 100°C, it has been shown that the permeability becomes more sensitive [21].It represented a model that considers the transfer of the oil phase from formation waters to rocks due to trapping effects.It dispersal, advection, and adsorption within the rock [22].The physical mechanisms of stable emulsion flow have been studied in sandstone systems with similar pore diameters.They have shown that the rheological change of emulsions in porous media is similar to that observed in viscometers of shear rates.A better understanding of the mechanisms by which oil/water emulsions flow through porous rocks is of paramount importance during re-drilling and improved oil recovery.Although a lot of research has been published on the process of O/W emulsion flow in porous media, the details of the mechanisms are still poorly understood.The main objective of the current study is to know the behavior of oil within the different porous media and its transmission method.In addition, the research looks at the extent of the various physical properties of the porous media on the oil.It controls its transmission speed through the medium and the extent of the effect of the mixing and heterogeneity between the two liquids on the method, transmission speed, and measured results.This study was limited to the horizontal runoff in the soil resulting from water-insoluble pollutants such as oil, and it can be developed in the future from By repeating the experiments vertically to study the vertical flow and the effect of gravity on it, as well as studying other types of two-phase flow contaminants and different soils .

Porous media
The oil transfer mechanism in a multi-porous medium was sieved using two distinct soil types, as seen in Figure 1.The first medium was sandy soil, sieves to eliminate impurities and large pebbles to obtain sandy soil with a suitable granular gradation.The second medium (organic matter) was composed of almost equal parts of sand, clay, silt, and algae soil.The soil of every kind was cleansed and dried.The fundamental physical characteristics of the media, including bulk density, sieve density, porosity, and permeability, were then estimated using the experiments listed in Table (1).

Pollutants
About 400 liters of white oil (kerosene) were utilized in this study.Kerosene is an oil distillate often used as a fuel or solvent.Kerosene is a transparent, odourless liquid made up of various hydrocarbons and may reach temperatures of up to 275 degrees Celsius.Coal, shale oil, and wood are among the potential kerosene sources, although refined petroleum is by far the most common.Kerosene was used for transmission through the soil and did not cause blockage of its pores or problems in the laboratory system because it is light oils.This is due to its low density, as the oils were classified into light and heavy according to their density measurement.Density is measured according to the specific density scale according to the American Petroleum Institute, and it has a mathematical formula for calculating the specific density.Accordingly, the oil is classified as "light" if its value is greater than 31.10,"medium" when values are between 22.30 and 31.10, and "heavy" when the API density is less than 22.30 [23].Kerosene, also known as paraffin, is a flammable hydrocarbon liquid derived from petroleum.It is widely used not only as aviation fuel but also in everyday life.Jet fuel is a complex mixture of aliphatic and aromatic hydrocarbons obtained by fractional distillation from crude oil.Its properties, combustion characteristics, and emissions result from a complex reaction of hundreds or thousands of different compounds, and crude kerosene makes it suitable for blending with performance additives in various commercial applications, including transportation fuel [24,25].Two different porous media were employed to fill the pipes, as indicated earlier.One tube was designated for sandy soil, while the other was for organic soil.To minimize voids, soil compaction was performed during routing.After that, two separate pollutant pumping tests were performed.
In the first experiment, water was pumped into both tubes, which lasted about two hours, after which the process of closing the water tank and opening the pollutant tank took place as the pumping of oil had been completed to 100%.The pumping continued until it was confirmed that the pollutant had reached the last point of withdrawal from each tube.Oil samples were drawn from both models along the pipeline at different times during the pumping process.The rise in pollutant percentage was calculated at each point over time.After ensuring that the oil reached the last point, the oil tank was closed, and the water began to be pumped again to obtain a washing process for the soil.During the washing process, samples were drawn for both models along the soil.The oil drop percentage was measured at each point.
All the steps taken in the first experiment were included in the second experiment.Still, the difference is that the oil and the water tanks were opened at the same time.The oil and water were mixed in the pipe's first section, which was empty, before entering the section with the remaining soil.The percentage of oil and water mixed in the discharge area was measured at about 20% oil to 80% water.During the pumping process, samples were taken to measure the percentage of water and oil at each point.After that, the washing process was carried out, and samples were taken.

First experiment (100% oil pumping)
The results of the 100% oil pumping process and then the washing process are shown in Figures 4-7.The figures indicate the results of calculating the percentage of oil in both phases of contamination and washing for both porous media.The contamination stage is when the oil is pumped only into the soil.Depending on the porous medium type, it lasts for different periods.The organic soil takes a longer pumping time for the pollutant to reach the pipe's last point and ensure its exit to the final drainage basin.The washing stage is the stage that follows the pollution stage, in which the oil pumping is stopped, and the water tank is opened to wash the soil of the pollutants.The time for washing also varies according to the porous medium, as the washing process in sandy soil is faster than in organic soil.
The results showed that on sandy soil, the pollutants run off faster, and the time taken is shorter for the pollution process as well as washing.The further it penetrates the soil, the farther it moves away from the pollution source, and the sooner the soil is washed.It takes a long time, which is also due to its physical properties, but it was found that the organic soil washes better than the sandy soil.

Second experiment (20% oil & 80% water mixing pumping).
The process here shows pumping oil and water simultaneously in the contamination stage with a mixing ratio of 20% oil to 80% water.Then the washing process is carried out, as illustrated in Figures 8-11.
Calculating the oil percentage in the pollution stage for both media shows a clear fluctuation in the sample reading.This is because the two liquids' viscosity, density, and flow speed differ.In small proportions to the soil, water enters faster and in larger quantities.After the oil particles entered the soil, it was noticed that after a short run-off distance, they would gather at a certain point inside the soil until they became a large amount.Then they would move again to the next points, but they would return to aggregation at another point until they reached a sufficient quantity that would allow them to flow again.Inside the pipeline, all this was happening because water affected oil flow into the soil.
This process was repeated throughout the contamination stage.In the washing stage for both mediums, the fluctuation was less, and the washing process was good and did not take long because the percentage of oil was not large inside the porous medium.

Conclusions
The results above show that when oil enters a porous medium, it is affected by the characteristics of the medium itself, the distance from the pollution area, and the mixing ratio.Similarly, it takes more time to wash the soil and remove the oil if it penetrates deeper into the soil.The results also show a difference in the behaviour of the pollutants in sandy soil compared with organic soil.The behavior of the pollutant when it enters the soil with the water at the same time (mixing ratio) caused a great fluctuation in the results compared with the case of no mixing ratio.This is due to the difference in viscosity, density, and other properties of both liquids.Also, the results showed that the time taken for the washing process in the mixing case is always less than the required time when the pollutant (oil) enters the soil alone.
The same system can be used by adding a mixer within the system's initial design inside the tube that helps mix the two-phase pollutants through multiple porous media, which can be different types of soil

Figure 1 .
Figure 1.Types of soil used in a laboratory model a) sandy soil b) organic soil

Figure 2 .
Figure 2. Sieving analysis results of the two mediums.

Figure 3 Figure 3 .
Figure3depicts the model designed and constructed in the lab to estimate the soil pollutant transport process.The model comprises a polyethylene pipe with a diameter of 0.08 meters and a length of 4 meters.There is a designated soil type for each tube.A 1.5-meter-high iron support held the tube in place.Small tubes with a diameter of 1 cm and a length of 3 cm are attached to each meter.They are used to remove samples of pollutants at predetermined intervals during the continuous operation.The pipe connected to a water tank with a capacity of 250 liters and an oil tank with a capacity of roughly 90 liters.The contaminated water discharged from the pipe's end is collected in a 250-liter tank.The volumetric approach was used to compute the system discharges from the volume of wastewater leaving this end pipe.

Figure 4 .
Figure 4. Percentage oil ratio in organic soil after pumping oil in 100% (contamination stage) , all time in minute.

Figure 5 .
Figure 5. Percentage oil ratio in sandy soil after pumping oil in 100% (contamination stage) , all time in minute.

Figure 6 .
Figure 6.Percentage oil ratio in organic soil after pumping water (washing stage) , all time in minute.

Figure 7 .
Figure 7. Percentage oil ratio in sandy soil after pumping water (washing stage) , all time in minute.

Figure 10 .
Figure 10.Percentage oil ratio in organic soil after pumping water only (washing stage) , all time in minute.

Figure 11 .
Figure 11.Percentage oil ratio in sandy soil after pumping water only (washing stage) , all time in minute.

Table . 1
. Properties of the two porous media.
SoilPermeability (m/s) Porosity Bulk density (g/cm 3 ) 1232 (2023) 012008 IOP Publishing doi:10.1088/1755-1315/1232/1/01200811 than those used in this research.The CFD simulation model is essential in simulating pollutant transport across porous media and comparing the findings to those of the physical model.