INVESTIGATING THE IMPACT OF EMULSION ON CRUDE OIL SEPARATION

INVESTIGATING THE IMPACT OF EMULSION ON CRUDE OIL SEPARATION

This study investigates the impact of emulsion on crude oil separation process. Emulsion Separation into oil and water requires the destabilization of emulsifying films around water drops. The effects of chemical demulsification operations on emulsion-break of water in crude oil emulsions were assessed using Amine group demulsifiers, acid demulsifier, and a polyhydric alcohol. For water in oil preparation, distilled was used as the water phase (dispersed phase) and crude oil as the oil phase (continuous phase). From the Analysis, Decylamine demulsifier is the best in terms of separation of both water and oil from Emulsion as it obtained 80% water and 87% oil, respectively.

The result shows that Amine group demulsifiers were more effective in emulsion breaking and should be used in Petroleum Industries.

CHAPTER ONE

 INTRODUCTION

An emulsion is a colloid of two or more immiscible liquids where one liquid contains a dispersion of the other liquids(Helmenstine 2018). It is a temporarily stable mixture of immiscible fluids, such as oil and water, achieved by finely dividing one phase into very small droplets. To form stable emulsions, there must be enough agitation or mixing energy to disperse one phase into the other and emulsifying agents (Surface active agents) such as asphaltic materials, resinous substances, oil-soluble Organic acids or finely dispersed solid materials must be present (Abdel-Aal et al., 2003).

Emulsions have important properties that may be desirable, for example, in a natural or formulated product, or undesirable, such as an unwanted emulsion in an industrial process.

Water is normally present in crude oil reservoirs or is injected as steam to stimulate oil production. Water and oil can mix while rising through the well and when passing through the valves and pumps to form in most cases relatively stable dispersions of water droplets in crude oil, which are usually referred to as oil field emulsions.

INVESTIGATING THE IMPACT OF EMULSION ON CRUDE OIL SEPARATION

1.1     Types of Oil Field Emulsion

1.1.1    Water-in-oil Emulsion (Normal Emulsion): This consists of water droplets in a continuous oil phase which can happen if water injection is used as the secondary drive.

Figure 1.1: Water in oil Emulsion

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1.1.2  Oil-in-water Emulsion (Reverse Emulsion): This consists of oil droplets in a water-continuous phase.

Figure 1.2: Oil in water Emulsion and crude oil separation

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Although water-in-oil emulsions are mostly encountered in the oil production industry, there are also cases of oil-in-water emulsions. This occurs due to the presence of a large amount of water as the continuous phase which can happen if water injection is used as the secondary drive. As the water amount continues to be increased, the water-in-oil emulsions will reach the phase inversion point. This is the point where a catastrophic inversion will occur, resulting in crude oil to become the dispersed phase, while water will become the continuous phase, i.e., oil-in-water emulsions (Alwadani, 2009).

In addition to the usual emulsion types, multiple emulsions, for instance, oil droplets dispersed in water droplets that are in turn dispersed in a continuous oil phase(Oil/water/oil) can occur. The type of emulsion that is formed depends upon a number of factors. If the ratio of the phase volumes is very large or very small, the phase having the smaller volume is frequently the dispersed phase. If the ratio is closer to 1, the other factors determine the type of emulsion formed.

1.2  Theory of Emulsion

An emulsion is a dispersion of droplets of one liquid (oil) in another liquid (water) with which it is incompletely immiscible. In an emulsion, the droplets often exceed the usual limits for colloids in sizes. Emulsion normally do not exist in the producing formation but are formed when oil and water are produced together with a great amount of agitation when water and oil in a reservoir enter the wellbore through the perforations in the casing, comparatively, large pressure differences are created which violently mix the produced oil and water together so that emulsion forms.

Three conditions must be satisfied for the formation of an emulsion

1. Two immiscible liquid must be mixed together.
2. These liquids must be thoroughly agitated to ensure the dispersion of one as droplet in the other (Fingas 2004).
3. An emulsifying agent which is a substance that helps an emulsion to become more stable and ensure that the oil phase is finely dispersed must be present.

1.1.1 Effects of Emulsions

In the oil production industry, emulsions can pose considerable flow assurance problems and greatly affect the capacity of separators, pumps, and pipelines.

A higher concentration of emulsions is also correlated to a larger value of pressure drop (Russell et al., 1959; Pal, 1993; Nadler and Mewes, 1997).  Water is normally presented in crude oil reservoirs or is injected as steam to simulate oil production (Hannisdal, 2005, Fingas et al., 2004).

Bancroft (1913) proposed that the stability of an emulsion is largely due to the nature of the interfacial film that is formed. The stability of this film is strongly dependent upon the surfactant adsorption-desorption Kinetics, solubility and interfacial tension gradient and interfacial viscosity.

A stable emulsion is composed of an aqueous phase, an oil phase, and an emulsifying agent. Particles and Surfactants found in crude oil can act as emulsifying agents and this can promote and stabilize water-in-oil emulsion (Bobra, 1990, 1991).

1.1.2    Factors that influence the stability of Emulsions

The adverse and beneficial effects of emulsions can be realized only if the emulsions are stable. If the emulsions are unstable, they will soon separate into two distinguished phases of water and oil and thus, the effects discussed earlier may no longer be applicable.

• Mixing Speed and Mixing duration: Generally, higher mixing speed and longer mixing duration would produce smaller sizes of emulsion droplets which have higher interfacial area and droplet-to-droplet interaction,       resulting in more stable emulsions (Ashrafizadeh and Kamran, 2010, Briceno et al, 1997, Pal et al, 1992).
• PH of Solution: Sakka (2003) and Yang et al. (2007) suggested that higher PH (Alkaline) would give more stability to the emulsions.

Tambe and Sharma (1993) maintained that in their studies, low PH values of 4-6 favoured oil in water emulsions, Sjoblom et al. (1990) put forward another point of view which generally believed that intermediate PH would cause instability, while either high or low PH values would help in stabilizing the emulsions.

• Temperature of Solution: Higher temperatures will first reduce the emulsions’ viscosity, eventually destabilizing and breaking the emulsions.
• Salt Concentration: The presence of salt in oilfield emulsion is real and should not be neglected; as the formation of water produced together with crude oil contains a certain amount of salt, known as oilfield brine.

In research conducted by Binks (1993), he claimed that higher salt concentration resulted in oil in water droplets to increase in size while water in oil droplets to decrease in size. Binks (1993) showed that higher salt concentration would destabilize oil in water emulsions but stabilize water in oil emulsions.

Ahmed et al. (1999) found out that higher salt concentration would result in lower interfacial tension of the oil droplets and the continuous water phase, facilitating the formation of smaller oil droplets which makes the oil in water emulsions to be more stable.

1.2 Statement of the Problem

Hydrocarbon resources are very important regarding the fact that they include about 65% of the world’s overall energy resources (Langevin et al, 2004 as cited in Ashrafizadeh and Kamran, 2010).

Emulsions may be encountered at all stages in the Petroleum recovery and processing industry (drilling fluid, Production, Process plant, and transportation emulsions). Pipeline emulsions flow is inevitable for upstream oil production system transporting mixtures of crude oil and water. The turbulence, mixing, as well as agitation through down hole wellbores, Surface chokes, valves, pumps and pipes will emulsify either the oil phase or water phase, depending on the volumetric amount of the phases (Fingas et al., 1993).

Oil will always be produced together with water from the reservoir and towards the end of the reservoir life.

It is interesting to note that while water-in-oil emulsions are undesirable, oil-in-water emulsions resolves the challenges of transporting highly viscous crude, as the emulsion system greatly reduces the effective viscosity (Lamb and Simpson, 1973., Ahmed et al, 1999).

The resolution of Crude oil Emulsion is vital to the Petroleum Industry because it helps to avoid the cost of transporting water, reduces the corrosion of pipelines, avoids the risk of poisoning catalysts and reduces oil-pumping costs. When oil contains water in form of an emulsion, the API gravity of the oil falls.

1.3 Aim and Objectives of the Study

The objective of this research is to study the effects of emulsions on crude oil separation and on the flow behaviours and flow properties as well as the influence of chemical demulsifiers on the destabilization of emulsions. Experimental results show a strong connection between good performance and the demulsifiers.

Crude oil separation emulsion must be separated almost completely before the oil can be transported and processed further. Emulsion separation into oil and water requires the destabilization of emulsifying films around water droplets.

1.4 Mode of Study

Chemical demulsification is the most widely applied method of treating water-in-crude oil emulsions and involves the use of chemical additives to accelerate the emulsion breaking process. The effect of chemical demulsification operations on the stability and properties of water-in-crude oil emulsions were assessed using Amine Demulsifier and Polyhydric Alcohol. Using samples of w/o, the data presented for several commercial-type demulsifiers show a strong connection (correlation) between good performance (fast coalescence) and the demulsifiers.

1.4.1 Chemical Method

The most common method of emulsion treatment is adding demulsifiers. These chemicals are designed to neutralize the stabilizing effect of emulsifying agents. Demulsifiers are surface-active compounds that, when added to the emulsion, migrate to the oil/water interface, rupture or weaken the rigid film, and enhance water droplet coalescence. Optimum emulsion breaking with a demulsifier requires a properly selected chemical for the given emulsion; adequate quantity of this chemical; adequate mixing of the chemical in the emulsion; and sufficient retention time in separators to settle water droplets. It may also require the addition of heat, electric grids, and coalescers to facilitate or completely resolve the emulsion.

1.4.2 Chemical Selection

The selection of the right demulsifier is crucial to emulsion breaking. The selection process for chemicals is still viewed as an art rather than a science. However, with the increasing understanding of emulsion mechanisms, the availability of new and improved chemicals, and new technology, research, and development efforts, the selection of the right chemical is becoming more scientific. Many of the failures of the past have been eliminated.

Demulsifier chemicals contain the following components:

1. Solvents
2. Surface-active ingredients
3. Flocculants

Solvents, such as benzene, toluene, xylene, short-chain alcohols, and heavy aromatic naptha, are generally carriers for the active ingredients of the demulsifier. Some solvents change the solubility conditions of the natural emulsifiers (e.g., asphaltenes) that are accumulated at the oil/brine interface. These solvents dissolve the indigenous surface-active agents back into the bulk phase, affecting the properties of the interfacial film that can facilitate coalescence and water separation.

Surface-active ingredients are chemicals that have surface-active properties characterized by hydrophilic-lipophilic balance (HLB) values. HLB(Hydrophile-Lipophile Balance) is an empirical expression for the relationship of the hydrophilic(“water-loving”)and hydrophobic (“water-hating”) groups of surfactant. The HLB scale varies from 0 to 20. A low HLB value refers to a hydrophilic or water-soluble surfactant. In general, natural emulsifiers that stabilize a water-in-oil emulsion exhibit an HLB value in the range of 3 to 8. Thus, demulsifiers with a high HLB value will destabilize these emulsions. The demulsifiers act by total or partial displacement of the indigenous stabilizing interfacial film components (polar materials) around the water droplets. This displacement also brings about a change in properties such as interfacial viscosity or elasticity of the protecting film, thus enhancing destabilization. In some cases, demulsifiers act as a wetting agent and change the wettability of the stabilizing particles, leading to a breakup of the emulsion film.

Flocculants are chemicals that flocculate the water droplets and facilitate coalescence. A detailed process for selecting the appropriate demulsifier chemicals includes the following steps:

1. Characterization of the crude oil and contaminants includes the API gravity of the crude oil, type and composition of oil and brine, inorganic solids, amount and type of salts, contaminant type and amounts.
2. Evaluation of operational data includes production rates, treating-vessel capabilities (residence time, electrostatic grids, temperature limitations, etc.), operating pressures and temperatures, chemical dosage equipment and injection points, sampling locations, maintenance frequency, and water rates.
3. Evaluation of emulsion-breaking performance: past experience and operating data including oil, water, and solids content during different tests; composition and quality of interface fluids; operating costs; and amounts of    water generated and its disposal.

Testing procedures are available to select appropriate chemicals. These tests include:

1. Bottle tests
2. Dynamic simulators
3. Actual plant tests

1.4.3 Chemical demulsifiers

Dehydration chemicals, or demulsifiers, are chemical compounds that are widely used to destabilize and assist in a coalescence of crude-oil emulsions. This treatment method is popular because the chemicals are easily applied, usually are reasonable in cost, and usually minimize the amount of heat and settling time required. The chemical counteracts the emulsifying agent, allowing the dispersed droplets of the emulsion to coalesce into larger drops and settle out of the matrix.

To work, demulsifiers:

1. Must be injected into the emulsion
2. Must mix intimately with the emulsion and migrate to all the protective films surrounding all the dispersed droplets
3. Must displace or nullify the effect of the emulsifying agent at the interface

For the oil and water to separate, there must also be a period of continual, moderate agitation of the treated emulsion to produce contact between and coalescence of the dispersed droplets, as well as a quiet settling period. Oil/water separation is usually based on a gravitational separation. Because water has a higher density than oil, water droplets have a tendency to settle down. Stokes’ Law approximates the settling rate of water droplets.

where:

v is the settling velocity of the water droplets

g is the acceleration caused by of gravity

r is the radius of the droplets

(ρ_w – ρ_o) is the density difference between the water and oil

μ is the oil viscosity

One way to help disperse the chemical throughout the emulsion is to mix a small volume of chemicals with a diluent and then to inject and mix the diluted chemical with the emulsion. The larger volume of the mixture can help to mix the chemical more uniformly and intimately with the emulsion. crude oil separation

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