BP Educational Service. Science at Work Discovering oil and gas

Transcription

1 BP Educational Service Science at Work Discovering oil and gas

2 Oil and gas formation Without oil and gas our lives would be totally different. We depend upon them for energy, plastics and even clothing. But where do oil and gas come from? The story begins over 150 million years ago. Ancient oceans teemed with microscopic creatures. When they died, they sank to the bottom of the sea. A layer of dead matter formed on the seabed. Over millions of years, sand and mud buried the dead matter. Sediments built up, pushing down on the matter below them. The pressure and temperature increased. High pressures and temperatures transformed the sediments and dead matter. The sand and mud became sedimentary rocks, such as chalk, limestone, sandstone and shale. The oil and gas formed many kilometres underground. They were squeezed by the high pressures and pushed into tiny pores in neighbouring rocks. The dead matter became crude oil and natural gas. 1. Oil and gas took millions of years to form. Why do you think they are called finite and non-renewable energy sources? 2. Why do BP geologists look for oil and gas where they find sedimentary rocks? 1

3 Where are oil and gas found? BP geologists use their understanding of the rocks they see on the surface of the Earth to help them understand the rocks that are buried underground. They can spot areas where oil and gas might be trapped underground by looking at aerial photographs of the surface. Impermeable rock Even after oil has formed in the rock, the pressure continues to rise. This squeezes the oil through rocks that have pores, or spaces, within them. Oil is forced into pores in surrounding rocks. Permeable rock Some oil eventually seeps naturally to the surface. Most oil meets a layer of rock that it can t move through. This impermeable rock forms a seal or trap. Very slowly, the oil builds up to form a reservoir. Impermeable and permeable rocks (greatly magnified) Reservoirs are rock formations that hold oil, natural gas or both within their pores, like a fossilised sponge. The pores also contain salt water. Reservoirs can be massive. Some may be as large as London. 3. How are oil and gas trapped to form a reservoir? Oil, salt water and gas have different densities. These densities change with temperature and pressure. For example, the density of natural gas increases when it is put under more pressure. The density of crude oil can also differ depending on whether it is a thin or thick crude. In one BP oil well, the densities in the reservoir are: Oil: 910 kg/m 3 Salt water: 1,025 kg/m 3 Natural gas: 410 kg/m 3 4. The oil, water and gas form three layers in the reservoir. Use the densities above to explain why, and to put the three layers in order. 2

4 Using waves to find oil and gas Drilling a well is extremely expensive. It s vital that BP can locate exactly where to drill. BP geophysicists must find the right spots in each oil field. Geophysicists use acoustic surveys known as seismic surveys to locate oil and gas. They use air guns to fire acoustic pulses down through the rock. These sound waves bounce back like echoes, revealing different layers of material and their depths. A powerful computer converts the sound patterns into a view of what lies underground. The data gives scientists the information they need to map reservoirs. They can identify whether the reservoirs are likely to be filled with oil, gas or just water (but they don t know for sure until they drill a well). Different rocks have different densities. Porous sandstone is less dense than heavy shale. Geophysicists know the density of each type of rock, and how fast sound waves travel through each one. 5. Why do you think sandstone is less dense than shale? BP geophysicists can direct sound waves at a rock formation from several different points, and measure how the waves are reflected. They use the data to work out the size and shape of the formation. One such formation is a cap of heavy shale. 6. Oil is sometimes found trapped beneath a cap. Shale is good at reflecting sound waves underground. Why does this mean that geophysicists must scan the rocks with sound waves from different points? Survey ship source of shock waves (air gun) hydrophones (for recording sound) sea bed sedimentary rock layers path of reflected waves impermeable rock water porous reservoir rock oil gas A seismic survey Seismic operations in Algeria 3

5 Visualising the world under your feet BP uses cutting-edge seismic technology to picture underground reservoirs. In a special room called a Highly Immersive Visual Environment (HIVE), geologists, geophysicists, computer scientists, drilling engineers and others come together to view the seismic data. Special glasses allow them to explore the reservoir in 3D. Seismic engineers create a series of images in vertical slices. HIVE puts these images together, like slices of bread in a loaf. Geologists can view the rocks from any angle by using HIVE to rotate the image. These images help BP to plan the next step: drilling into soil and rock to find out for certain whether oil or gas are present. Inside the HIVE 7. Why might a detailed, 3D image help BP to make the most of each oil field? Scientists and engineers can now take seismic surveys into the fourth dimension time. They scan the oil field every few months or years to build up a '4D' picture of how the oil and gas have changed position over time. These are important tools. In most oil fields, engineers have to inject water to help push the oil to the surface. They inject water down wells in the oil field, and this pushes the oil out through wells at other locations. Detailed 3D and 4D surveillance allows the engineers to inject the water in the most effective places, and to monitor how the water injection is working. 8. Remember that substances with different densities reflect sound waves in different ways. How might the densities of oil and water allow BP engineers to see how an oil field has changed over time? What s really exciting is that seismic surveillance has a direct impact on our day-to-day business. Seismic advisor, BP 4

6 The products of oil and gas 9. In a small group, list all the products you can see around you that are made from oil. How many did you spot? What other products that come from oil might you have used since you got up this morning? Nearly every molecule in oil or gas is made up of just two elements: hydrogen and carbon. These elements combine in chains to create molecules called hydrocarbons. Chemists can alter hydrocarbon molecules to change their properties. They can: join small molecules together to form longer chains or break long-chain molecules into smaller ones Hydrocarbon molecules Noticeboard pins one use for plastics made from oil 10.Some crude oils are more valuable than others. Refineries pay more for thin, pale oils than for thick, heavy oils. Why do you think this might be? Chemists can overcome differences in crude oil. They help BP refineries to modify the hydrocarbons each crude contains. This helps each refinery to meet its customers needs. These processes allow many different products to be made from crude oil. Oil and gas from different reservoirs formed under different conditions. They were created from different marine creatures, and experienced different temperatures, pressures and cooking times. This makes the oil and gas in each reservoir unique. For example, some oils from South America are thick and tarry, while many from North Africa are thinner and lighter. 5

7 Hydrocarbons and the future Oil and gas are essential. They power transport and homes, and they provide thousands of products from bottles to medicines. Scientists carefully distinguish among proven fact, informed speculation and blind faith. Scientists are certain that oil and gas are finite resources. Almost since the beginning of the oil industry over 150 years ago, people have warned that supplies will run out. No-one knows how long supplies will last. Chief scientist, BP The amount of oil and gas that we know exists has changed over time, and so has the amount that can be extracted. 11. Why might these amounts of oil and gas change? BP needs to understand how much oil and gas might be available in the future. It needs to predict where new technologies could help to locate and recover more reserves. For example, many new oil fields are located under seawater up to 3,000m deep. BP is investing in new technologies that allow it to work in these conditions. Scientists are also developing other technologies: Different sources of energy, for example wind power, or technologies that use natural gas or hydrogen New ways to recycle more waste plastic 12. Why might recycling become more important as oil reserves get smaller? Biofuel 6

8 Glossary Acoustic to do with sound; an acoustic wave is a sound wave. Density the mass per unit of volume; shows how tightly packed together the substance is. Impermeable does not allow liquids or gases to pass through. Porous full of tiny holes or passages. Pressure the amount of force acting on a surface or volume. Reservoir a place where a volume of oil or gas is trapped. Seismic technology using acoustic waves to explore rock formations deep underground. Shale soft, finely layered sedimentary rock formed from mud or clay. BP Educational Service PO Box 105, Rochester, Kent, ME2 4BE Tel: +44 (0) Fax: +44 (0) bpes@bp.com Website: BP International Ltd 2008