نطق چهارم

Lecture 4 - Petroleum

Listen to part of a lecture in a geology class.

Professor: Hi, class, let’s get started. Um, last time we finished up the section of coal, so we have just two fossil fuels left to talk about. Those are petroleum and natural gas. Today I will concentrate on petroleum and we will get into natural gas tomorrow. Like coal and natural gas, petroleum has been formed over millions of years, from the remains of prehistoric plants and animals.

And like coal and natural gas, it’s found in the rocks of Earth’s crusts. In fact, the word “petroleum” literally means “rock oil”. And in its’ original state, the way we find it in Earth’s crust, it is called crude oil, sometime people will short it up, and just refer to it as crude.

Um, petroleum also contains natural gas, so usually the petroleum industry is naturally searching for and utilizing deposits of both crude oil and natural gas at the same time. In other words, companies might as well gather, use and sell both the oil and the gas when they find it, since both are valuable. Ann?

Student: But what kind of organic materials, I mean, specifically what kind of dead plants and animals make up petroleum exactly? Do you mean like trees and dinosaurs?

Professor: Well, apparently petroleum is usually made from simple, one-celled marine animals and plants, algae, for example. Um, what happens is this accumulated plant and animal material that originally came from the ocean gets covered by sediment. And then is…um, eventually exposed to earth internal heat and pressure, for millions of years. And over those millions of years, the heat cooks and the pressure molds that material, turning it into a thick, sticky liquid.

And since petroleum is made from these ocean organisms, you can guess where it was found, makes sense that we usually find it under the ocean or near shore, right? Yes, Ann?

Ann: I’ve heard people talk of……ah……live and dead oils?

Professor: Well, um, when crude oil has a lot of natural gas mixed up with it, it’s called live oil. But if the gas escapes from the mixture, then the oil is said to be dead. And it’s heavy and more difficult to pump. Does anyone know how the gas separates from the oil? Sam, go ahead.

Sam: Doesn’t it happen when the oil shoots up to the surface?

Professor: Yes, that’s right. When oil reaches the surface of the Earth, there is less pressure on it. And with less pressure, the oil and gas were able to separate. The other way the crude oil was able to come up to the surface is by people pumping it up out of the ground. And, um, it’s the same thing that happens at the surface, there is less pressure, and, so the oil and gas separate. But when we talked about how it actually exists inside earth’s crust, most people think that there are huge, pools of oil sitting around in caverns somewhere under there. That’s really rare. The majority of petroleum is just filling in the tiny pores and cracks in rocks.

Now, um, a little more on the petroleum industry. As far as the extraction process the petroleum industry digs deep wells to reach underground oil fields where crude oil has accumulated over a large area and extract between layers of rocks. Then it pumps the crude oil out. Then its refineries have two main tasks, convert less valuable crude oil into a more valuable form and create usable products from refined oil. Basically, the refiner will do this by boiling the oil.

When the oil cools off, the stuff that is left is turned into a variety of products, like gasoline, diesel fuel for cars and trucks, asphalt for roads, um, paints, plastics, even soaps. And check what you’re wearing, if you are wearing something with synthetic fibers, what that really means is that it is made of the petroleum. So you can see petroleum is essential to today’s industrial society.

Now, next week we will be joining graduate students from the department of petroleum engineering to examine the comprehensive field study they’re working on in our local oil fields. And I’d like you to read over the pack of information I’m about to hand out to you before we go. It should familiarize you with the history of the oil field we will be touring as well as the details of their project.