THE PHYSICAL AND CHEMICAL PROPERTIES OF PETROLEUM

SHAN SHAHZAD – 41Contact Email:

ahmadraza2502@gmail.comUNIVERSITY OF THE PUNJAB

LAHORE

INTRODUCTION

• Oil and gas are two chemically and physically diverse groups of compounds termed as hydrocarbons.

• Physically, hydrocarbons grade from gases, via liquids and plastic substances to solids.

• The hydrocarbon gases include dry gas (methane) and the wet gases ( ethane, propane, butane etc.)

• Condensates: are H.C that are gaseous in the sub-surface, but condense to liquid when they are cooled at the surface.

• Liquid H.C are termed as oil, crude oil, or just crude.

• The plastic H.C include asphalt & related substances.

• Solid H.C include coal and Kerogen.

Basic Terms

• Natural Gas: “ H.C & non H.C (gas or in soln.) with crude oil in underground reservoirs”.

• It is divided into three types :• Dissolved Gas: is in soln. with crude oil in the

reservoir.• Associated Gas: commonly known as gas cap,

overlies & is in contact with crude oil in the reservoir.

• Non-Associated Gas: is in the reservoir that don’t contain significant quantities of crude oil.

• Gases are classified as dry or wet according to the amount of liquid vapor that they contain.

• Dry Gas: A dry gas is a gas with < 0.1 gal/ 1000ft3 of condensate. e.g! Methane.

• Wet Gas: A wet gas is a gas with >0.3 gal/1000ft3 of condensate. e.g! ethane, propane, butane.

• Refining: The process of separating the various constituents/ Fractions of petroleum is known as refining. It is carried out in a petroleum refinery.

• Porous Rock: Rock, which contains pores in it.• Permeable Rock: Rock, which contains interconnected

pores in it.• Source Rock: “ Porous Rock, which generate

hydrocarbons”.• Reservoir Rock: “Porous and permeable rock unit, which

holds hydrocarbons”.• Seal Rock: “Porous & impermeable Rock which seal or

stop the upward movement of oil.• Organic Matter can be usefully divided into two

components:• Bitumen: which is composed of compounds that are soluble

in organic solvents; and• kerogen: the insoluble components.

Natural Gases• There are 2 categories :• Hydrocarbon Gases: 1. Methane 2. Ethane 3. Propane etc. • Non Hydrocarbon Gases: 1. Inert Gases 2. Nitrogen 3.Hydrogen 4.CO2

5.H2S

Hydrocarbon Gases

• The major constituents of natural gas are the H.C of the Paraffin series.

• The heavier members of the series decline in abundance with increasing molecular weight.

Methane• Methane is also known as “Marsh Gas” if it is found at

the surface. • It is called “fire Damp” if it is present down a coal mine.• Occurrence: Traces of methane are commonly recoded

as shale gas or background gas during the drilling of all. It is produced by the destructive distillation of coal .

• Properties: Colorless, flammable gas, sparingly soluble in H2O and lighter than air.

• Use: Domestic purposes in Europe until replaced by Natural Gas, itself largely composed of methane

Sources of Methane:• Three Sources: 1. Mantle 2. Thermal Maturation of Buried O.M. 3. Bacterial degradation of O.M.Other H.C: • They don’t form biogenically.• They are only produced by the thermal

maturation of O.M• If they detected during drilling, indicates

proximity to a significant petroleum accumulation or source rock.

Non-Hydrocarbon Gases

• Inert Gases: He is minor accessory in many natural Gases & traces of Ar & Radon have also been found in the sub-surface.

• He occur in Atm. At 5ppm & also recorded in mines, hot springs & fumaroles.

• Sources: He is produced by the decay of various radioactive elements, principally U, Th, radium.

• Use: It can b used in dirigibles• Hazards: Radon may cause lung cancer.

Nitrogen

N2: Frequently occurs naturally & associated with both inert gases & H.C.Sources: • Volcanic eruption & I.R .• N2 also form organically as by the degradation

of nitrates via ammonia. But only in shallow conditions

• Some Atm. N2 may occur as a connate gas.

Hydrogen & CO2Hydrogen:• Free H2 gas rarely occurs in the sub-surface, partly

because of its reactivity & partly because of its mobility.

• H2 is commonly dissolved in sub-surface H2O & in petroleum as traces. • Subsurface H2 is probably produced by the thermal

maturation of O.M.CO2:• CO2 is found as a minor accessory in H.C natural gases.• It is also associated with N2 & He.

Sources: has both organic & inorganic sources.• It is a major constituent of volcanic activity and EQ.• Permeable L.st and Dolomite can also yield CO2 .

• Thermal maturation of kerogen.• CH4 in the presence of Oxygenated H2O may yield

CO & H2O.• Uses: Dry Ice and to enhance the oil recovery.

Hydrogen Sulfide• H2S occurs in sub-surface both as free gas and

in solution because of its high solubility with brine and oil.

Properties: Poisonous , evil-smelling gas, highly corrosive to steel & quickly attacking production pipes.On the basis of presence of SO2, gases may be Sour Gas: Gas or oil containing significant traces of SO2.

Sweet Gas: Oil or gas without H2S.

Sources: It is commonly expelled from volcanic eruption.• Euxinic environments, such as black sea.• Anhydrite in the presence of O.M converted

into calcite & giving off H2S.• It is also associated with evaporites &

carbonates.Hazards: Small traces of H2S may caused:• Corrosion • Washing plants.

Gas HydratesDefinition: Compounds of frozen water contain gas molecules are known as “hydrates”.Clathrates: The ice molecules themselves are referred to as “Clathrates”. Properties: Look similar to white, powdery snow.Structure: It has 2 types of unit structures:-Small Structures : Small structure with a lattice structure of 12A0 holds upto 8 CH4 within 46 H2O molecules.• This clathrates may contain not only methane but also

ethane, H2S,CO2.

• Larger Structure: with a lattice structure of 17.4 A0,

consists of 136 H2O molecules.• This clathrate can hold the larger H.C molecules of

the pentane & n-butanes.

Occurences and sources: They occur only in specific PT conditions.• They are stable at high P and low T.

• They also has shallow biogenic origin.• They also occur in deep ocean deposits.Economic Significance:• They are climate change indicator.• Due to low permeability, they form seal that

prevent upward movement of free gas.

Crude Oil

• A mixture of H.C that existed in the liquid phase at atm. pressure.

• Properties: It may be yellow, green, & brown to dark brown or black in color.

• Oil are naturally viscous & and oily.• Surface oil is more viscous than sub-surface

oil.

Chemistry• H. Series: The components of natural

hydrocarbons belong to 4 groups or series: Paraffins or n-alkanes : Are straight chain series, with the general formula CnH2n+2.• For n = 1 to 4, these are gases.• They are the most abundant H.C present in

both gaseous and liquid petroleum. E.g! Methane etc

Naphthenes: Also called Cycloparaffins or cylcloalkanes.• Are a closed ring series with the general formula CnH2n,

form saturated ring. • Unlike parafins, all napthenes are liquid at normal T.• They make up about 40% of both light & heavy crude oil. Aromatics: generally a minor group of hydrocarbons that contain at least• one benzene ring (C6H6) in which all carbons share the

fourth bond. • They are present in all petroleum except their %age are

small. E.g Benzene, Toluene etc.

Resins and Asphaltenes:• Are composed of fused benzene ring networks,

but they contain impurity atoms like N,S,O. • They are not true H.C. • These impurities are the high molecular weight.• They are the heaviest components of crude oil .

Crude oil Classification

THANK YOUBeware the man who has received charity from you