Abstract
This report entails the study of the effect of the foaming agents in the physio-chemical properties of the oil system, this report investigate if the addition of such foaming agents can improve production and also determines the properties of the crude oil and the foaming agents used. The properties investigated are Density, Specific Gravity, API gravity, viscosity, Surface Tension and Pour point before and after the addition of the foaming agents. The effects of foaming agents in crude oil: it increases density, viscosity and specific gravity of crude oil and decreases API gravity, surface tension, pour and cloud point of crude oil.
Statistical and graphical analysis were used to interpret the results of the experiments carried out. The results show that foaming agents increases oil density, oil viscosity, oil specific gravity and decreases oil API gravity, oil surface tension, oil cloud point and pour point.
The study would help petroleum engineers to understand the positive impac
CHAPTER ONE
INTRODUCTION
1.1 Crude Oil System
Crude Oil or Petroleum refers to any naturally-occurring flammable hydrocarbon mixture found in geologic formations, such as rock strata, formed through the heating and compression of organic material such as dead zooplankton and algae over a long period of time. Technically, the term petroleum only refers to crude oil, but sometimes it is applied to describe any solid, liquid or gaseous hydrocarbons. It is a hydrocarbon mixture having simple to most complex structures such as resins, asphaltenes etc. Crude oil can be refined to produce usable products such as gasoline, diesel and various forms of petrochemicals.
Crude oil is also a naturally occurring mixture, consisting of hydrocarbon with other element such as sulphur, nitrogen, oxygen, etc. appearing in the form of organic compounds which in some cases form complexes with metals. Elemental analysis of crude oil shows that it contains mainly carbon and hydrogen in the appropriate ration of six to one by weight. The mixture of hydrocarbon is highly complex, and the complexity increases with boiling range.
Crude oil is formed by bacterial transformation of Organic matter (carbohydrates/proteins/ animal origin) by decay in presence and/or absence of air into HC rich sediments by undergoing biological/physical and chemical alterations In its strictest sense, crude oil, but in common usage it includes all liquid, gaseous, and solid hydrocarbons. Under surface pressure and temperature conditions, lighter hydrocarbons methane, ethane, propane and butane occur as gases, while pentane and heavier ones are in the form of liquids or solids. However, in an underground oil reservoir the proportions of gas, liquid, and solid depend on subsurface conditions and on the phase diagram of the crude mixture.
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1.2 Properties of crude oil system
Density
Density is defined as the mass per unit volume of a substance. It is most often reported for oils in units of g/mL or g/cm3, and less often in units of kg/m3. Density is temperature-dependent. Oil will float on water if the density of the oil is less than that of the water. This will be true of all fresh crude oils, and most fuel oils, for both salt and fresh water. Bitumen and certain residual fuel oils may have densities greater than 1.0 g/mL and their buoyancy behaviour will vary depending on the salinity and temperature of the water. The density of spilled oil will also increase with time, as the more volatile (and less dense) components are lost. After considerable evaporation, the density of some crude oils may increase enough for the oils to submerge below the water surface.
Two density-related properties of oils are often used: specific gravity and American Petroleum Institute (API) gravity. Specific gravity (or relative density) is the ratio, at a specified temperature, of the oil density to the density of pure water. The API gravity scale arbitrarily assigns an API gravity of 10° to pure water. API gravity is
Calculated as:
API gravity (o) = (141.5/ (specific gravity (60/60oF) – 131.5 ………………………………… (1)
Oils with low densities, and hence low specific gravities, have high API gravities. The price of a crude oil is usually based on its API gravity, with high gravity oils commanding higher prices.
Pour Point
The pour point of an oil is the lowest temperature at which the oil will just flow, under standard test conditions. The failure to flow at the pour point is usually attributed to the
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separation of waxes from the oil, but can also be due to the effect of viscosity in the case of very viscous oils. Also, particularly in the case of residual fuel oils, Pour points may be influenced by the thermal history of the sample, that is, the degree and duration of heating and cooling to which the sample has been exposed. From a spill response point of view, it must be emphasized that the tendency of the oil to flow will be influenced by the size and shape of the container, the head of the oil, and the physical structure of the solidified oil. The pour point of the oils is therefore an indication, and not an exact measure, of the temperature at which flow ceases.
Viscosity
Dynamic Viscosity: Viscosity is a measure of a fluid’s resistance to flow; the lower the viscosity of a fluid, the more easily it flows.
Like density, viscosity is affected by temperature. As temperature decreases, viscosity increases. The SI unit of dynamic viscosity is the millipascal-second (mPa∙s). This is equivalent to the former unit of centipoise (cp). Viscosity is a very important property of oils because it affects the rate at which crude oil will spread, the degree to which it will penetrate shoreline substrates, and the selection of mechanical spill countermeasures equipment.
Viscosity measurements may be absolute or relative (sometimes called ‘apparent’). Absolute viscosities are those measured by a standard method, with the results traceable to fundamental units. Absolute viscosities are distinguished from relative measurements made with instruments that measure viscous drag in a fluid, without known and/or uniform applied shear rates.
Sulphur
The sulphur content of a crude oil is important for a number of reasons. Downstream processes such as catalytic cracking and refining will be adversely affected by high sulphur
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contents. Crude oil containing a high amount of the impurity (sulfur) is referred to as sour crude oil, when the total sulfur level in the oil is more than 0.5% the oil is called “sourâ€Â. The impurity needs to be removed before this lower-quality crude can be refined into petrol, thereby increasing the cost of processing. The majority of the sulfur in crude oil occurs bonded to carbon atoms, with a small amount occurring as elemental sulfur in solution and as hydrogen sulfide gas. Sour oil can be toxic and corrosive, especially when the oil contains higher levels of hydrogen sulphide, which is a breathing hazard. At low concentrations the gas gives the oil the smell of rotting eggs. For safety reasons, sour crude oil needs to be stabilized by having hydrogen sulfide gas (H2S) removed from it before being transported by oil tankers. This results in a higher-priced gasoline than that made from sweet crude oil.
Basic Sediment and Water Content (BS&W) Basic sediment and water (BS&W) is a technical specification of certain impurities in crude oil. When extracted from an oil reservoir, the crude oil contains some amount of water and suspended solids from the reservoir. The particulate matter is known as sediment or mud. The water content can vary greatly from field to field, and may be present in large quantities for older fields, or if oil extraction is enhanced using water injection technology. The bulk of the water and sediment is usually separated at the field to minimize the quantity that needs to be transported further. The residual content of these unwanted impurities is measured as BS&W. Oil refineries may either buy crude to a certain BS&W specification or may alternatively have initial crude oil dehydration and desalting process units that reduce the BS&W to acceptable limits, or a combination thereof.
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Chemical Composition of Crude oil
Carbon – 83.0 to 87.0%
Hydrogen – 10.0 to 14.0 %
Sulphur – 0.05 to 6.0 %
Nitrogen – 0.1 to 2.0 %
Oxygen – 0.05 to 1.5 %
Metals – 0.00 to 0.14 %
1.3 Characterization of Crude Oil
Crude oil is a naturally occurring liquid, mineral oil consisting of a variety of organic compounds, mainly saturated and aromatic hydrocarbons, but also more complex compounds. The oil industry characterizes the quality of the oil using:
API Gravity
The American Petroleum Institute gravity, or API gravity, is a measure of how heavy or light a petroleum liquid is compared to water: if its API gravity is greater than 10, it is lighter and floats on water; if less than 10, it is heavier and sinks. The API degrees indicate whether a crude oil floats on water or sinks, Higher API gravity is preferred in the petroleum industry.(API gravity > 10)
API gravity (o) = (141.5/ (density at 60oF)) – 131.5 ………………………………………. (2)
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Viscosity
It is the resistance to flow, usually measured @ 100oF in centistokes (kinematic viscosity). Crude oil with low viscosity is preferred in the petroleum industry because it receives a higher price than heavy crude oil on commodity markets because it produces a higher percentage of gasoline and diesel fuel when converted into products by an oil refinery.
Surface Tension
Surface tension is the elastic tendency of liquids which makes them acquire the least surface area possible. Surface tension is an important property that markedly influences oil production. It is also referred to as the force that holds the surface of a particular phase together and is normally measured in dynes/cm.
Pour Point
The pour point of a liquid is the temperature at which it becomes semi solid and loses its flow characteristics. In crude oil a high pour point is generally associated with a high paraffin content, typically found in crude derived from a larger proportion of plant material.
Flash Point
The flash point of crude oil is the temperature above which the oil will spontaneously combust. The flash point of a volatile material is the lowest temperature at which it can vaporizes to form an ignitable mixture in air.
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1.4 Foaming Agents
A foaming agent is a material that facilitates formation of foam such as a surfactant or a blowing agent. A surfactant, when present in small amounts of crude oil, reduces surface tension of the oil (reduces the work needed to create the foam) or increases its colloidal stability by inhibiting coalescence of bubbles. A blowing agent is a gas that forms the gaseous part of the foam.
A foam on the other hand is a dispersion of gas in liquid, usually with a surface-active agent present. Foams are not thermo-dynamically stable and ultimately decay into their constituent phases, but can be mechanically stable. When a foam exists inside a confining medium, dimensions of this confining medium relative to the average bubble size determine the texture and properties of the foam. When the confining diameter is large relative to typical bubble size, such as in a pipe, the foam is similar to bulk foam. Its flow can then be treated as that of a non-Newtonian, compressible pseudo fluid.
The ability of foam to reduce gas mobility has led to its application in a number of processes, including gas flooding, steam flooding, and oil reservoir treatment techniques. It has been somewhat uncertain whether foam in these cases actually works by gas blockage and flow diversion, or whether it is better described as a “viscosifying agent†for the gas.
Foams often forms in crude oil by adding foaming agents, it also formed as the crude oil pressure is reduced in the reservoir, well bore, tubing string or flow line. In short, foam forms essentially instantaneously after a pressure drop. Many crude oils have the potential of creating foam carry-over, even though it is popular to blame a factor such as asphaltenes, paraffin, emulsions, high crude viscosities, or poorly designed internals around the crude oil,
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Surfactants
Surfactants are compounds that lower the surface tension (or interfacial tension) between two liquids or between a liquid and a solid. Surfactants may act as detergents, wetting agents, emulsifiers, foaming agents, and dispersants. Surfactants are usually organic compounds that are amphiphilic, meaning they contain both hydrophobic groups (their tails) and hydrophilicgroups (their heads). Therefore, a surfactant contains both a water insoluble (and oil soluble) component and a water soluble component. Surfactants will diffuse in water and adsorb at interfaces between air and water or at the interface between oil and water, in the case where water is mixed with oil. Sodium laureth sulphate, or sodium lauryl ether sulphate (SLES) for example , is a detergent and surfactant found in many personal care products (soaps, shampoos, toothpastes, etc.). It is an inexpensive and effective foamer. Sodium lauryl sulfate (also known as sodium dodecyl sulfate or SDS) and ammonium lauryl sulfate (ALS) are commonly used alternatives to SLES in consumer products.
1.5 Factors Contributing to Crude Oil Foam Formation
The amount of foam that a crude oil system can create, the stability of the foaming agent or the foam and even, the capacity to create gas/ liquid films depend on the characteristics of the gas dissolved. Gases that do not have an affinity for the crude oil tend to form unstable foams. However, if the gas is soluble in the oil, foams can be formed and the extent will depend on the pressure and temperature of the system.
The initial Gas to Oil Ratio (GOR) in the crude oil determines the quantity of gas that can be released, which is related to the foam formation. It also bears on foam stability by the number of bubbles and their size distribution. Sheng J.J.et al (1997), the composition of the crude oil is equally important to the eventual foaming properties. There are several
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constituents that can promote the formation of foam and/or stabilize it once it is generated. For example, Callaghan I.C.et al (1985), have found that short-chain carboxylic acids and phenols with a molecular mass lower than 400 are responsible for foam production. Other authors evoke asphaltenes and resins as the primary cause of foam. Poindexter M.K., et al (2002), identified several parameters that are important for controlling the foaming behaviour of crude-oils, which include bulk viscosity and density, oil-gas surface tension, asphaltenes and resins content and their molecular weight.
Viscosity plays an important role in any foam (aqueous or non-aqueous) because it is directly related to the drainage of interstitial fluid in the foam. In addition to lowering the drainage rate, high viscosity systems can also lower the rate of gas diffusion between bubbles (Ostwald ripening) and both effects tend to promote foam stability. In fact, Poindexter et al. (2002), indicate that crude oils with bulk viscosities lower than 150cp at 37.8 o C produce little or no foam. On the other hand, Fraga A.K.et al (2011), have evaluated high viscosity oils and find that these oils did not generate foams even when they contain high levels of stabilizing species. As with aqueous foam, the surface properties of liquid-gas interface in crude-oil foam are also important. In particular it has been found that the surface rheological Behaviour plays an important role in stabilizing the Thin-liquid films in the foam.
The presence of other phases apart from oil and gas, such as water or solids, can also influence the foam behaviour and stability. Along these lines Marcano L., et al (2009), have studied the stability of foams formed from Diesel oil and fatty acids surfactants (to simulate Venezuelan crude oils) with dispersed water. They found that it is possible to create stable foam by adding water at concentrations higher than 2%. They suggest that when water is present in the system, the bubbles formed will be surrounded by water and dispersed in the oil, originating an air/water/oil dispersed system stabilized by the mixture of surfactants, the low molecular weight surfactants being adsorbed at the air/water interface, and the high
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molecular weight surfactants being adsorbed at the water/oil interface. In their review on foamy oil flow, Sheng J.J., et al (1999), indicate that the presence of water has no measurable effect on the nucleation of bubbles, hence on bubble frequency but it has an influence on the rheological behaviour of the mixtures.
Viscosity of the water-in-oil emulsion. As already mentioned, the presence of solid particles at the interface (sand, aggregates, salts, etc.) can stabilize foam. Furthermore, foam creation and stability can also be enhanced in solid porous media. Sheng et al. (1997) indicate higher stability foam can be achieved in a porous media than that in a bulk vessel. This effect is a consequence of the wetting behaviour of the media and its subsequent influence on the capillary pressure imposed on the thin foam films.
1.6 Properties of foam
When foaming agents are added to crude oil it forms foams. Foams are a structured two phase in liquid dispersions, whose rheological properties are difficult and on the other hand, the physical properties are easy to determine
Rheological properties : The two phase nature of foams suggest its non-Newtonian behaviour, all fluids which do not exhibit direct proportionality between shear stress and shear rate at a constant temperature and pressure, are generally classified as non-Newtonian while all fluids or substances that direct proportionality between shear stress and shear rate follows the viscous law’s.
For Newtonians fluid, the stress acting on an elements of material is proportional to the corresponding time derivative of strain (the constant of proportionality is called the viscosity) and the viscosity is independent of time and strain measured from any reference state.