Module Code: EAX_4_272 Title: Reservoir Fluid Properties

Modular weight: 10 Examination weighting: 70 %

Prerequisite modules: MENG01C02.

Reassessment: No restrictions.

Internal Examiner/Module Leader: Dr/ Ramadan Emara

Semester taught: Two

Key words: phase fluid behavior, reservoir fluid characteristics.

Date of latest revision:

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[PTRL04C02]

Reservoir Fluid Properties

AimsThe aim of this module is to introduce students to thevarious properties of petroleum reservoir fluids, wherecertain fundamental concepts form the foundation onwhich petroleum engineering is based. In this modulefluid phase behaviour in single and multi-componentsystems and reservoir fluid characteristics arepresented.

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Content

• behaviour of gases;

• phase behaviour of liquids;

• qualitative phase behaviour of hydrocarbon systems;

• quantitative phase behaviour;

• reservoir fluid characteristics;

• applications of reservoir fluid characteristics;

• PVT analysis.

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Reading List

• E.J. Burcik, "Properties of Petroleum Reservoir Fluids", IHRDC, ISBN: 0934634009 (1979)

• McCain Jr., William D., "The properties of Petroleum Fluids", Pennwell Publishing , ISBN: 0878143351 (1973)

• Abhijit T Dandekar, "Petroleum Reservoir Rock and Fluid Properties", Taylor and Francis, ISBN: 9780849330438 (2006)

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Chapter 1

Introduction To Petroleum Reservoir Fluids

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Reservoir is a subsurface, porous, permeable rockbody in which oil and/or gas has accumulated.

Most reservoir rocks are limestones, dolomites,sandstones, or a combination.

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Sandstone Limestone Dolomite

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In the typical oil reservoir, gas, oil, and water becomevertically segregated because of their differentdensities. Gas, the lightest, occupies the upper partof the reservoir rocks; water, the lower part; and oil,the intermediate section.

Petroleum is a substance occurring naturally in theearth in solid, liquid, or gaseous state and composedmainly of mixtures of chemical compounds of carbon andhydrogen, with or without other nonmetallic elementssuch as sulphur, oxygen, and nitrogen.

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Solid Liquid Gas

Sulphur Oxygen Nitrogen

Petroleum Chemistry

• The branch of chemistry that deals with petroleum iscalled organic chemistry because it involves thechemistry of compounds of carbon and is connected toliving organisms that make up the two major sources oforganic material, petroleum and coal, from whichorganic compounds are obtained.

• Both these compounds are products of decayed plantsand animals and are prominently considered in theorganic theory of the formation of petroleum.

• Organic chemicals is usually named on the basis of asystem developed by the International Union of Pureand Applied Chemistry (IUPAC).

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• According to IUPAC, hydrocarbons areclassified into the following categories asshown in the following slide, most of whichdescribe series (known as homologous series)of compounds having a common basiccharacteristic or structure, and differing onlyin the number of structural carbon atoms (andhence molecular weight).

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Aliphatics Aromatics(arenes)

Alkanes(Paraffins)CnH2n+2

AlkenesCnH2n

AlkynesCnH2n-2

Cycloaliphatics(Naphthenes)

CnH2n

Alkanes (paraffins)• This particular series of hydrocarbons has a general

formula, CnH2n+2, where n denotes the number ofcarbon atoms.

• The alkanes are named through the combination of aprefix (signifying the number of carbon atoms) and asuffix that ends with "-ane."

• Compounds belonging to this series are sometimescalled saturated hydrocarbons because the carbonatoms are attached to as many hydrogen atoms aspossible, that is, the carbon atoms are saturated withhydrogen. However, they are commonly known asparaffins in the petroleum industry.

• Examples of well-known alkanes or paraffins are given inthe following Table.

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The structural formulas for methane (smallesthydrocarbon found in reservoir fluids). ethane andpropane are shown in the following Figure.

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• However, as the carbon number increases, carbon atomsmay be connected in continuous chains or as brancheswith more than two carbon atoms linked together. thefollowing Figure in the next slide shows this connectionfor pentane having carbon number five.

• Continuous chain hydrocarbons are known as normalhydrocarbon and a prefix "normal" or simply "n" isattached to the name.

• The prefix "iso-" is used for substances with two methylgroups (CH3) attached to carbon atoms at the end of anotherwise straight chain.

• The prefix "neo-" denotes three methyl groups attachedto carbon atoms at the end of a chain.

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• The number of possible structures increases with thenumber of carbon atoms in the molecule. For example,decane (carbon number 10) has 75 such configurations.These configurations are called structural isomers or, simply,isomers, meaning they have the same molecular formula,C4H10 or C5H12, but different arrangements of atoms.

• In spite of the molecular weight remains the same, certainphysical properties are different. For example, n-butane hasa boiling point of 31.1F, but iso-butane boils at 10.9F.

• At normal pressure and temperature conditions, whencarbon numbers range from 1 to 4, the resultingcompounds are gases; while carbon numbers that rangefrom 5 to 17 are mainly liquids. Carbon numbers higherthan 17 have a solid appearance.2/10/2015 Dr.Ramadan Emara 17

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Standard Condition

Physical Properties of Alkanes

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Alkenes (olefins)• This family of hydrocarbons is also called olefins and is

commonly known by that name in the petroleum andpetrochemical industries.

• The general formula for olefins is CnH2n,. Commonexamples of alkenes or olefins include ethylene andpropylene.

• The presence of olefins in naturally occurringhydrocarbons is usually a rare occurrence. On the otherhand", olefins are actually produced in petrochemicalcomplexes based on the feedstock, usually composedof light alkanes.

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Alkynes

• The general formula for alkynes is CnH2n-2. Commonexamples of alkynes include substances such asacetylene.

• Similar to alkenes, alkynes are also rarely found innaturally occurring hydrocarbons and are usuallyproduced in petrochemical plants that use lighterhydrocarbons as feedstock.

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Cycloaliphatics (naphthenes)• In many hydrocarbon compounds, carbon atoms are

arranged in rings instead of chains, as seen in the caseof normal alkanes. These types of compounds arecalled cyclic compounds and include cycloalkanes andcycloalkenes.

• Cycloalkanes or cycloparaffins are commonly known inthe petroleum industry as naphthenes.

• The general formula is given by CnH2n. Commonexamples of naphthenes include cyclopentane andcyclohexane and have structures as shown in thefollowing Figure.

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Aromatics• This class of hydrocarbons is also called arenes. the

name aromatics comes from the fact that manycompounds belonging to this class have very pleasantodors. However, these compounds are generally verytoxic and some are carcinogenic.

• Benzene, having the chemical formula C6H6, is one ofthe most commonly known aromatic compounds,characterized by the six carbon atoms arranged in ahexagonal ring structure, known as the benzene ring.The six hydrogen atoms are associated with eachcarbon, as shown in the benzene ring structure in thefollowing Figure.

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Nonhydrocarbon in Reservoir Fluids

• Reservoir gases and oils also contain certainnonhydrocarbon components. Commonly foundnonhydrocarbon components include nitrogen (N2),carbon dioxide (CO2), and hydrogen sulfide (H2S).

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Nitrogenhydrogen sulfideCarbon dioxide

The Solid Components Of Petroleum

• All activities in the oil and gas industry, upstream(production), midstream (transportation), anddownstream (refining), are frequently affected by thesolid components of petroleum.

• The solid components of petroleum are sometimesreferred to as unique phases and include gas hydrates,waxes and asphaltenes.

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Gas Hydrates• These are defined as solid, semistable compounds that

are basically light hydrocarbon molecules (e.g.,methane or ethane) occupying the geometric latticesof water molecules and having snow-like appearances.For example, natural gas hydrates are usually formedwhenever natural gas, water, and appropriatetemperature and pressure conditions exist.

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Waxes• Waxes can be defined as solids deposited from crude

oils when cooled below a certain temperature. Thedeposited solids are called waxes and are generallycomposed of heavy paraffins (e.g. n-hexadecane andhigher).

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Asphaltenes

• Asphaltenes is characterized as organic materialsconsisting of aromatic and naphthenic ringcompounds containing nitrogen, sulfur, andoxygen molecules.

• The asphaltene fraction of a crude oil is definedas the organic part of the oil that is not soluble innormal alkane solvents such as pentane orheptane.

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Classification Of Reservoir Gases And Oils

• Compositional analysis of reservoir gases is readilyobtained by techniques such as gas chromatographyand low-temperature distillation.

• For physical classification of reservoir gases, gasgravity is frequently used as a characterizationparameter.

• Gas gravity is defined as the ratio of gas density andair density at the same pressure and temperatureconditions.

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Chemical Classification of Reservoir Oils• The chemical classification of reservoir oils is not as simple

as gases because the size range of molecules can be huge.For instance, the smallest molecule is methane, CH4, with amolecular weight of 16 (12 carbon atoms and 4 hydrogenatoms), while the largest molecules can have molecularweights as high as 10,000.

• Therefore, instead of identifying each and every componentin reservoir oils, which is practically impossible anyway, theaverage chemical analysis of oils includes paraffins-isoparaffins-aromatics-naphthenes-olefins (PIANO) or PONAanalysis, and in the latter case all paraffins are combinedwhile other groups remain as they are. However, consideringthe rarity of olefins in reservoir oils and the lumping of allthe paraffins, chemical analysis is simplified or reduced toonly the determination of paraffins, naphthenes, andaromatics, known as PNA analysis.

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Physical Classification of Crude Oils

• reservoir oils are classified according to variousphysical properties that include specific gravity, color,sulfur content, odor, and viscosity. Among thesevarious physical properties, the most important isspecific gravity.

• The specific gravity of a crude oil (or any liquid) isdefined as the ratio of the density of the oil and thedensity of water at specified pressure andtemperature conditions.

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• The petroleum industry also uses another gravityscale known as API (American Petroleum Institute)gravity, defined as

where API is the API gravity and ϒo the specific gravity

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