OIL AND GAS – BLACK GOLD: PRESENTATION NOTES
INTRODUCTORY SLIDES
SLIDE 1. OIL AND GAS – BLACK GOLD
Presenter notes: Oil and Gas are natural resources of enormous economic importance. Together they provide about 60% of all the energy used by society today. They provide fuel for transport and are vital for heating, lighting and cooking. In addition they are used in the manufacture of synthetic fabrics, plastics, fertilizers, detergent as well as for many other purposes. In short, it is hard to imagine how our society could function without oil and gas.
Additional background notes for the presenter: It would be useful if the presenter brought along some rock samples as props. These could include an organic rich mudstone (black shale) to illustrate a source rock such as the Kimmeridge Clay (see slide 11), an impermeable rock to illustrate the cap such as halite (see slide 13) and a porous sandstone to illustrate a reservoir rock such as the Penrith Sandstone (see slide 13-14).
SLIDE 2. TALK OUTLINE
Presenter notes: In this talk we will examine oil and gas from three angles.
In the first part we will think about the biological and geological processes responsible for the formation of oil and gas. In Practical Exercise 1 we investigate the rate at which oil and gas deposits form and consider the meaning of non-renewable versus renewable energy.
In the second part, we will look at the way geologists explore for new oil and gas deposits and consider the how oil and gas get from the well to the marketplace. In Practical Exercise 2, we will have a chance to explore for oil and gas fields ourselves in the ‘Prospector Game’.
In the third part, we will examine the political importance of oil and gas. Specifically we will look at which countries control production, consider global supply and demand, and think about the likely future of oil and gas in our society.
PART 1: ORIGIN
SLIDE 3. CHEMISTRY
Questions for discussion: What is oil and gas? Where does it come from?
Presenter notes: As we begin to think about the origin of oil and gas, a basic question we need to answer is what exactly are oil and gas? Oil and gas are complicated mixtures of different hydrocarbons. A hydrocarbon is a large organic molecule. As the name suggests it is composed of hydrogen atoms attached to a backbone, or chain, of carbon atoms. Short chain hydrocarbons like methane are gases. Medium chain hydrocarbons like paraffin are liquids. Long chain hydrocarbons like bitumen are solids. When crude oil is extracted from the earth it may be a mixture of hydrocarbons in solid, liquid and gas states.
SLIDE 4. PLANKTON
Presenter notes: It may come as a surprise but most of the world’s oil and gas is made up of the fossil remains of microscopic marine plants and animals. That’s why oil and gas are often referred to as a fossil fuel. One of the most important groups of plankton involved in the formation of oil and gas are single-celled marine ‘plants’ called dinoflagellates, though many types of animal plankton are also important. Some oil and gas may have also originated from the remains of land plants, but we will not discuss these types of deposits in this talk.
SLIDE 5. BLOOMS
Presenter notes: In certain parts of the world’s oceans, plankton occurs in enormous quantities, or blooms. Exactly where those plankton blooms occur is controlled by ocean currents. The richest sites are where cold, nutrient rich waters rise to the surface from the deepest parts of the ocean. The nutrients found in these ‘upwelling zones’ feed plankton and allow them to reproduce quickly. A single litre of seawater may contain several million dinoflagellates. Where these plankton occurs in high numbers they may turn the water red. This phenomenon is known as red tide.
SLIDE 6. ON THE SEA BED
Presenter notes: When plankton dies it slowly settles to the sea bed where it forms an organic mush. Usually there are lots of animals living on the sea floor that feed on this material. One important group is the polychaete worms. These are detritivores, which means they eat the dead and decay remains of other organisms
SLIDE 7. BLACK SHALE
Presenter notes: However, under certain conditions there may be very little oxygen on the sea floor. This may be because the ocean is deep and stagnant and oxygen has not been mixed down from the surface waters. No animal life can survive where the sea bed is completely lacking oxygen. Without animals to eat the dead plankton, the organic mush builds up on the sea bed. Where ocean sediment contains more than 5% organic mush it eventually forms a rock known as a Black Shale. The black colour comes from the dark organic matter that it contains. As we will see, Black Shale is what makes oil and gas.
SLIDE 8. COOKING
Presenter notes: As more sediment accumulates on top, layers of Black Shale become buried more and more deeply in the Earth’s crust. As they do so, they slowly heat up because of the geothermal gradient. With progressive heating the organic material in the plankton undergoes chemical and physical changes. It gradually breaks down into smaller and smaller hydrocarbons. At temperatures of around 30°C, a solid, sticky bitumen is produced. Around 90°C liquid oil is formed. As temperatures reach 150°C, natural gases like methane are given off. A Black Shale that is heated and gives off oil and gas is known in the oil industry as a Source Rock.
Background notes: This is natural chemical ‘cracking’ of the hydrocarbons – where the initially large molecules are broken into progressively smaller molecules by the increase in temperature – much the same as long chain hydrocarbons can be ‘cracked’ commercially.
SLIDE 9. MIGRATION
Presenter notes: The hot oil and gas does not stay in the Source Rock for long. As the hydrocarbons are less dense than the water in the source rocks that surround them, they gradually migrate upwards through the rock in much the same way that the less dense air bubbles of an underwater diver will rise through water. The migrating oil and gas may travel up through the spaces between the sand grains that make up the rock (called pores) or they may find their way up through cracks, fissures, and faults in the overlying rocks. As we will see when we look at oil exploration, eventually oil and gas get trapped in pockets of rock known as reservoirs.
SLIDE 10. ANCIENT EARTH
Presenter notes: Most of the Source Rocks that gave rise to our present day oilfields were formed in the middle of the Mesozoic Era about 150 million years ago. At that time conditions were just right to build up huge thicknesses of Black Shale. On the one hand, the oceans were unusually warm, promoting vast plankton blooms. On the other hand, oxygen was mostly absent on the ocean floors so most of the plankton that settled on the bottom accumulated. There were no animals around to eat it up. The map on the left hand side shows what the Earth looked like 150 million years ago. The red circles show where the world’s main oil deposits were formed in warm, shallow, deoxygenated seas.
SLIDE 11. SOURCE OF NORTH SEA OIL
Presenter notes: A real example of a Black Shale that has formed a major oil deposit is the Jurassic Kimmeridge Clay. This is a 150 million year old shale that contains up to 50% organic matter. It stretches from Dorset in southern England right across to Norway. It was this Black Shale which was the main Source Rock for the North Sea oilfield.
SLIDE 12. PRACTICAL EXERCISE 1
Presenter notes: The Kimmeridge Clay of Dorset took an enormous amount of geological time to form (perhaps as long as 5-10 million years). After that it took still many more million years before it was sufficiently cooked to start producing oil and gas. In the first Practical Exercise we will try and calculate exactly how much time it takes to form a watt of energy from oil and gas by biological and geological processes. We will compare our figures with other energy sources like solar power and think about the meaning of Non-renewable and Renewable Energy.
PART 2: EXPLORATION AND PRODUCTION
SLIDE 13. OIL TRAPS
Presenter notes: In the first practical we thought about the immense amount of time it takes to form oil and gas. Consequently, it is an extremely valuable resource and huge amounts of money are poured into trying to locate new oilfields. In this section, we will investigate how reservoirs of oil and gas are discovered and how it eventually reaches the marketplace.
As we have already seen, once produced, oil and gas migrates out of its Source Rock and accumulates in overlying rocks. Some rocks like sandstone or limestone are permeable to oil and gas, which means that they can pass freely through them. Other rocks like clay or salt are impermeable, which means they block the upward passage of hydrocarbons.
One of the most common ways that oil and gas becomes trapped in pockets in the rock is where it is rises into a structural dome capped by impermeable rocks. The cap rocks prevent the oil and gas escaping upwards. The buoyancy of the less dense hydrocarbons in the pore waters prevents them from sinking back down. This is an example of an Oil Trap.
Optional exercise: An excellent additional exercise to get students thinking further about how Oil Traps form go to http://earthlearningidea.com, click on Earth-related Activities, and look under the Resource and Environment section.
SLIDE 14. RESERVOIR ROCK
Presenter notes: The permeable rocks than contain oil and gas within the oil trap are known as the Reservoir Rock. Reservoir rocks have lots of interconnected holes called pores. These allow them to absorb the oil and gas like a sponge. The picture on the left shows a good reservoir rock with lots of pore spaces filled with water shown in blue. As we advance the slide, we see the pores gradually fill with oil. This rock can soak up a large amount of oil.
SLIDE 15. SEISMIC SURVEY
Presenter notes: We’ve just established what kind of structures tend to trap oil and gas in the Earth’s crust, but how do we locate potential traps underground? One technique is to use seismic surveys. In this technique, a Vibrator Truck fires shock waves into the ground. The shock waves pass through some rock layers and bounce off others. By recording how long it takes for the shock waves to arrive back at the surface allows geologist to build a picture of the internal structure of the rocks beneath their feet. An example of a seismic survey is shown in the diagram on the right. It reveals a large underground dome in the rocks. As we have seen domes often trap oil and gas so this may be a potential site to drill.
SLIDE 16. DRILLING THE WELL
Presenter notes: A potential oil trap is called a Prospect. Once a prospect has been identified, the next stage is to drill a hole into the top of the trap to see if it contains oil and gas. It is incredibly expensive to a drill hole. On an offshore rig is may cost $10,000 million for every metre drilled. So if you are going to drill a hole 5000 metres underground it’s going to cost you 20 million pounds/ 25 million dollars! Consequently geologists have to be pretty confident that they going to hit oil. If they drill too many ‘dry holes’ they will soon lose their jobs!
SLIDE 17. ENHANCED RECOVERY
Presenter: If the geologist is lucky, he or she will strike oil and gas. A hole which contains oil and gas is called a well. The oil and gas is under considerable pressure in the Earth’s crust so once a well is drilled into the reservoir rock, the oil and gas rapidly rises to the surface. However, as more and more oil and gas comes out of the well, eventually the pressure drops and flow slows down.
To get the remainder of the oil and gas out of the reservoir rock, a second hole is drilled adjacent to the first. Hot water or steam is pumped down the hole and this forces the oil and gas still trapped in the rock up the original well. This technique is known as enhanced recovery.
SLIDE 18. TRANSPORT
Presenter notes: Once the oil and gas has been extracted from the ground, it must be safely transported from the well to the refinery where it will be processed. Oil is usually transported from the well to the refinery using pipelines. These may stretch over land or be laid over the sea bed. A spectacular example of an oil pipeline is the Trans-Alaskan pipeline which carries oil and gas for 1300 kilometres across Arctic permafrost. Another way that oil and gas are transported is by means of massive oil tankers. These gigantic vessels can carry up to half a million tonnes of oil.
SLIDE 19. AT THE REFINERY
Presenter notes: At the refinery, the crude oil, which also contains a lot of gas, is processed. This involves separating out all the different hydrocarbons in the crude oil. To do this, the crude oil is heated in a furnace and then passed through a cooling tower. The method relies on the fact that different hydrocarbons have different boiling points. Consequently the heavy hydrocarbons like bitumen with high boiling points accumulate at the bottom of the cooling tower. Light hydrocarbons like paraffin with low boiling points accumulate near the top of the top. This process is known as fractional distillation. The different hydrocarbons have different uses. For example, bitumen is used to surface roads while paraffin is mostly used as aviation fuel.
SLIDE 20. EARLY HISTORY
Presenter notes: People have been using oil and gas for four thousand years. However, the modern era of oil and gas exploration and production didn’t begin until 1846. That year, Abraham Gesner, a geologist based in New Brunswick, Canada figured out how to distill paraffin from crude oil. This made crude oil far more useful and triggered a global boom is exploration and production. California became an early centre of oil prospecting and was famous for its gushers. These were pressurized oil reservoirs, which when drilled, spurted massive fountains of oil into the air!