Exploring for Petroleum
To learn about petroleum exploration beneath Earth's surface.
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Geoscientists know that they are not likely to find petroleum just anywhere. Only certain kinds of places are likely to contain good petroleum reservoirs. An essential characteristic of oil-bearing regions is a thick sequence of sedimentary rocks. Geoscientists also know that only certain kinds of sedimentary rocks are likely to form petroleum source and reservoir rocks. In most cases, after studying maps and cross-sections, geoscientists searching for oil must drill test wells. The rock fragments from inside the borehole, as well the cores themselves reveal important information about the potential for oil and its extraction. However, the drilling process is both time consuming and expensive, especially if the well is dry because there is either no oil, or the well misses the oil.
To get the best picture of oil-bearing structures scientists use seismic studies or seismology. This involves generating seismic waves that pass into the Earth. These waves are partially reflected along bedding planes and other structures within the crust to the surface where they are recorded. Computer models are used to compile the data and produce two- or three-dimensional models similar to those used in medical imaging.
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Groups of students build a model of rock layers in a box or tray. Boxes are exchanged with other groups. Layers of sediment used in the models should be slightly dampened so that students can extract rock cores and determine the stratigraphy of the rock units. Following this, a balloon of oil is placed in a box and surrounded by rock chips. Students apply a seismic sounding technique to determine the location of the oil. Students are given a budget that constrains the number of boreholes they can drill to find the reservoir.
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Materials and Equipment
small deep clear box, three different colored sands, marker pens, clear plastic drinking straws, graph paper, ruler, small cardboard box with a lid, small rock samples, balloon filled with black colored water or oil, masking tape, bamboo skewer, or stud finder
Part A: Exploring Subsurface Rock Structures
- Ask students to place an uneven layer of sand about 2.5 cm thick in a tray. Have them make a sketch or take a photograph of the layer. This will be used later to test the models made by other groups.
- Have students repeat this process by adding a second and a third layer of different colored sand. The layers should be irregular. Make sure that the students record their shapes and dimensions.
- Ask students to mark the compass directions (north, east, south, and west) on each side of the box.
- Have students exchange their rock layer model with another group.
- Ask students to devise a method to map the region in their model. They may use: clear plastic drinking straws, marker pens, graph paper, and a ruler.
- After they have completed their models, ask students to compare them to the photographs and drawings of the group that originally made the model.
- As a class, have students compare their methods with those used by other groups.
Answers will vary depending on the methods selected. Groups may apply systematic or random approaches with varying degrees of success.
- Have students find out how exploration geologists examine subsurface rocks and structures. Ask them to find out:
- What techniques and tools do they use?
Geologists use a variety of methods including surface mapping of rock outcrops, sampling of subsurface rocks and layers using boreholes and logging techniques, seismic surveys, and digital modeling.
- What difficulties do they have to overcome in collecting data and producing models?
More often than not, geologists can only make limited observations from surface exposures. To overcome this they learn as much as they can from good exposures and apply knowledge to less well known sequences with similar characteristics. Sampling everywhere is impossible. Scientists must select their sample sites and methods very carefully to get the best data they can make models. They must also apply caution when extrapolating between data points during the modeling process.
Part B: Modeling an Oil Reserve
- Ask students to partially fill a shoe box with sand. Have them carefully select a location to place an oil balloon (oil reservoir) and surround it with smaller rocks. They should then fill the box to the top with sand. Instruct them to place a lid on the box and secure it with tape.
- Students will receive a box from another group. Ask them to attach a sheet of graph paper to the lid of the box.
- Have students place the box on the table and gently tap on the box lid to listen for different sounds.
- Ask students to record the areas which they think might be worth investigating.
Students should explore areas with interesting or different sounds.
- Ask them to mark off divisions of one centimeter on a bamboo skewer, starting at the bottom.
- Tell students to carefully probe for oil. Tell them that every centimeter they drill costs $200,000. Each time they start a new test site it costs an additional $100,000 dollars.
Ask students to:
- Record their drilling strategy and its costs.
Answers will vary between groups.
- Have students keep drilling until they find oil.
- Once all the groups have successfully located their reservoir, have the class discuss their different strategies.
- Ask students to answer the following:
- Which group had the most cost effective result, why?
Many factors are involved in making the models and devising sampling strategies. Answers will vary between groups.
- How might drilling beneath the oceans be especially difficult?
The distances involved are immense and the ocean surface is constantly moving. The structures beneath the ocean are covered by sediments and water and difficult to see. Because of the distances involved any error in drilling is often magnified.
- Do you think your method would be effective for discovering natural gas? Explain.
Natural gas has a lower density than both the surrounding rocks and neighboring petroleum deposits. Methods that test density or gravity would be effective.
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