PETROLEUM CHEMISTRY CHAPTER-1 INTRODUCTION By Dr. Ghulam Abbas Department of Chemical and Biological Sciences, University of Nizwa.

Introduction What is petroleum/crude oil? How does it formed __ the basic origin?? What are fossil fuels?? Oil and gas formation Petroleum reservoirs inside earth Geological distribution of reservoirs Composition of crude oil? Classification of crude oil Oil as a source of energy

Introduction Fossil fuels are the world’s most commonly used energy source. Fossils are stores of energy formed from the remains of plants and animals that lived millions of years ago – hence the name fossil fuels. Coal, oil and natural gas are examples of fossil fuels.

How crude oil and gas (fossil fuel) is formed?? It was formed from the remains of dead animals and plants that lived in a marine (water) environment millions of years ago. When organisms died and sank to the bottom, they were covered in mud, sand and other mineral deposits. This organic matter, mixed with sediments (layers) of sand and mud, is slowly buried beneath even more sediments deposited by the rivers and seas.

As these sediments (organic matter, mixed with sand and mud) become more deeply buried, the pressures and temperatures within them increase. The increasing temperature and pressure slowly change the sediments into what we call sedimentary rocks, such as chalk, limestone, sandstone and shale. The lack of oxygen in the sedimentary layers caused organisms to slowly convert into carbon-rich compounds called kerogen. The rocks that contain the kerogen and from which the oil and gas are generated are called source rocks.

As more layers deposited on top of one another, pressure and heat acting on the source rock chemically converted the kerogen into crude oil and natural gas. As a general rule, whether the conditions lead to the formation of oil or natural gas depends upon temperature; the hotter the conditions, the more likely it would lead to the formation of natural gas. This process is called generation.

How crude oil and gas (fossil fuel) is formed??

Fossil fuels have taken millions of years to form Crude oil is made from dead plants, trees and water animals that died millions of years ago ➔ (moving to the sea-bed) These animals were buried under layers of sand and sink on the bottom of the sea (Slow decaying) Due to this compact layering, this material did not decay as normal because of no oxygen (source Rock Formation) These sediments became more deeply buried and the increasing temperature and pressure slowly changed the sediment into rock (Kerogen Formation) The dead organic matter transformed into kerogen (carbon-rich compound) (Crude oil and natural gas Formation) More heat & pressure converts kerogen into Crude oil and natural gas

Petroleum Reservoirs Because petroleum is a fluid, it is able to migrate through the earth as it forms. To form large, economically recoverable amounts of oil underground, two things are needed: an oil pool (reservoir) and an oil trap. Crude oil produced by source rocks will migrate into a "reservoir" rock, known as an oil pool. A reservoir rock, like sandstone, has “pores (spaces) " of the rock for oil to reside.

Reservoir rocks must need a non-porous covering known as oil trap above and below so the oil is "trapped“ in the ground, so that they cannot flow to the surface of the earth. This oil trap is impermeable rock, a non-porous rock (for example shale) that holds the oil pool in place. Non-porous rock has no holes, and acts as a barrier to prevent the oil and natural gas rising.

Petroleum Reservoirs Gas, oil, and water in a reservoir rock

Geological distribution of petroleum reserves A hot, wet climate fosters the growth of large amounts of organisms. If this growth takes place in a shallow sea, the eventual drying out of the environment and evaporation of the sea water leaves behind large deposits of salt. Salt makes an excellent cap rock for a reservoir. These are precisely the conditions that prevailed in the Middle East, giving rise to the enormous deposits of oil found in that region of the world.

Geological distribution of petroleum reserves

Composition of crude oil Mostly of hydrocarbons with small amounts of nitrogen, oxygen or sulfur. It may also contain trace amounts of metals such as Iron (Fe) Nickel (Ni), copper (Cu)and Vanadium (V) Elemental composition by weight

Hydrocarbons in Crude oil Most of the compounds contain from five to about twenty carbon atoms. Among these some are: Straight chain/Branched (paraffins) Ring structure or cyclic compounds (Naphthanes) Aromatic compounds Hydrocarbon name Common name General Formula By weight composition Paraffins Alkanes (Saturated) CnH2n+2 30 Naphthanes Cycloalkane (Saturated) CnH2n 49 Aromatics Aromatic (unsaturated) CnHn 15

Classification of crude oils Crude oil varies in appearance depending upon its composition as black, dark brown or greenish Depending upon the physical state these are classified as: Young shallow crudes Young deep crudes Old shallow crudes Old deep crudes

1. Young shallow crudes Young because: they have not had long time to be broken down by high temperature inside the earth Shallow because: they have not been burried so deeply (not deep) In Young shallow crudes, the long-chain compounds in the kerogen will not have broken apart to a great extent, because the oil or kerogen has not yet been buried very deeply (so it has not been exposed to high temperatures in the earth), nor has it been buried for a very long time. The carbon atom chains in this oil are likely to be very long. These long chains give the crude oil two properties:

They make it dense because long, straight chains of molecules can be packed tightly, resulting in a large mass per unit volume. They also make it difficult for the molecules to flow past one another, making the crude oil more viscous (slower to flow and harder to pump). In addition, many sulfur compounds might be present in these oils. Typically, young-shallow crudes are highly viscous, high-density materials high sulfur content

2. Young Deep crudes Young : they have not had long time to be buried Deep because: they have been burried so deeply (so deep) As the oil is buried more deeply inside the earth's crust, it is exposed to higher temperatures. As a result, the molecules can break apart to a greater extent, and some of the molecules containing sulfur will be destroyed. These ‘young-deep’ crudes will have: moderate viscosities, densities and sulfur contents.

3. Old-Shallow crudes Old because : they have had long time to be buried ‘old-shallow’ oil have the same properties as a young-deep one. If the oil has not been buried very deeply, it will not experience the same temperatures as a young-deep crude. However, over very long time periods, the same chemical transformations that occur in a short time at high temperatures can also occur at relatively low temperatures. Thus an ‘old-shallow’ oil might have the same properties as a young-deep one.

4. Old-Deep crudes If a crude oil is buried deeply and for a long time, extensive breaking apart of the carbon chains can occur. At the same time, most of the sulfur compounds in the oil are broken down. Therefore an ‘old-deep’ crude oil has low viscosity, low density, and Very low sulfur content. This combination of properties makes the old-deep crudes the most desirable: they require little refining to remove sulfur and they can be converted to large quantities of high-quality products. Unfortunately, less than 5% of the world's remaining petroleum reserves are of this quality.

Classification of crude oils