Coring Is Not Boring!
2A: Building a Model Core Drill
How Does the JOIDES Resolution Obtain Sediment Cores?
The JOIDES Resolution is one of the premier science research vessels in the world. Unlike other ocean-going ships, it is outfitted with a huge 62 meter tall derrick to support its core drilling function. When the JOIDES Resolution reaches the drilling site, the crew keeps the vessel over the precise location of the site using 12 computer-controlled thrusters as well as a main propulsion system. When assembled, the rig can suspend up to 9,150 m (over 5.5 miles!) of drill pipe in ocean depths as great as 8,235 m (about 5 miles).
Near the center of the research vessel is the "moon pool," a 7m (23 ft.) wide hole through which the assembled string of drilling pipe is lowered into the ocean. Each piece of pipe is about 28 m (93 ft.) and weighs about 874 kg (1925 lb.). A massive drill bit is affixed to the end of the first piece of pipe.
The drill crew uses the draw works to thread each piece of pipe together to form the drill string. After they have assembled the string, which can be up to six miles in length, it is lowered through to depths ranging from a 100 to thousands of meters of ocean water over a period of twelve hours. To core through the seafloor, the crew uses a motorized system to rotate the entire drill string. The thrusters keep the massive vessel itself from rotating along with the drill pipe. This ship moves to several sites during each expedition and drills operate continuously once in place.
The drill crew can use two different types of drills to bring up cores. If the sediment layers are fine grained (mud) or sand, a piston corer is used. It uses a piston-like action to shoot the hollow drill pipe through the layers of sediment in a matter of seconds. The pipe, now filled with sediment is then slowly brought up to the surface. On the other hand, if the crew has to drill through denser sediments or layers of rock, a rotary core barrel is used. The drill string has a bit and outer core barrel attached to it. The bit rotates with the drill string while the inner core barrel stays remains stationary. The bit trims a 2.3 meter core. When the inner barrel holds about 10 m of core, it is brought to the surface.
Lab Procedure
Part A - Build a Model Drill
In this part of the activity, you will build a simple model of the JOIDES Resolution coring apparatus. Your goal is to recover a core sample from a model of the ocean floor composed of different layers of clay. The following are the materials you will use to build your model:
- Popsicle sticks
- Small binder clamps
- Spool of thread
- Clear straws
- Transparent tape
- Rubber bands
- PlayDoh
- A model of sediments on the ocean floor (see your teacher)
1. Read about and look at more images of How we drill and core in hard sediments and rocks. It illustrates how cores are gathered by the JOIDES Resolution.
2. Your model will also use a hollow pipe or tube (clear straw) to sample the sedimentary layers at the test site. Instead of using the force of pressurized water to force your coring device through the sediment, you will use extra weight(s) on your coring drill to sample at least two layers. You are not allowed to lower or push your coring apparatus down into the sediment layers by hand. In this model, your device represents the coring drill on the JOIDES Resolution, the foot of air it passes through represents the ocean, and the PlayDoh layers at the test site represents the sediment layers the expedition will explore at each of the sites it visits.
3. Brainstorm and Design - Look at the materials you were given to build the drill.
4. Build - Use the materials provided to build a device that can lower a drill string and take a core sample of at least two layers below. If you have difficulty in the design process, see your teacher for a picture of a sample model.
Part B - Test, Evaluate, and Redesign
Now that you have built an initial model drill, you will need to test your drill's effectiveness in drilling though several layers of sediment (PlayDoh).
4. Obtain a small amount of two different colors of PlayDoh. Knead the clay into two flat disks about 10 cm across. Place the two layers on top of each other.
5. Test and Evaluate - Position your drill about 1 foot above the two layers. Release the drill. Watch how it interacts with the PlayDoh layers.
· Did your drill penetrate to the bottom of all the layers?
· Did your drill capture a core sample?
6. Make several other trials and think of changes that you can make to make your drill more efficient at taking cores samples.
7. You may have found that your prototype needs a redesign. Remember that the design process is all about "If at first you don't succeed, then try, try again." Study any problems and then redesign.
8. Final Test – Your teacher will show you the testing area and instruct your group where your core should be taken. You will add your core to the rest of those gathered from other groups to determine what lies under the surface of this model seabed.
9. Analyze Results – Your teacher will assemble the class results. As a class, answer the following questions.
Stop and Think
1. How many sedimentary layers (called strata distinct horizontal layers in geological deposits. Each layer may differ from adjacent layers in terms of texture, grain size, chemical composition, or other geological criteria. ) are present in the test area?
2. Trace out the approximate outline of the second layer (called a lens of sedimentary material) with a dotted line on a separate piece of paper. Use the coordinates of the test area to sketch the layer in as close to true scale as you can.
3. Assuming that the test area sediment layers were laid down by a river emptying into a bay or ocean, what kind of event in the Earth system might be responsible for depositing the lens of material?
4. If the PlayDoh layers were replaced by a stack of graham crackers, how would have to modify the design of your drill?
Going Further
Draw a Cross Section of Sediment BedsProcedure
1. Geologists usually construct a cross-section of rock strata to help them understand the rock record, the geologic history of a region.
2. You can draw a cross section of the layers in your PlayDoh model by making a set of measurements, and then drawing a graph.
Note: Your core sections must be taken along a straight line across the PlayDoh.
3. Measure the distance (in mm) of the core sample positions, starting with zero on the right hand. Record in a table.
4. For each core site/position, measure the thickness of each colored clay layer. Record these numbers. Also note the total thickness of layers at each site. Note: You may want to multiply these numbers by 10 to make them easier to plot.
4. Since you are drawing a picture of what lies below the surface, draw a horizontal line on a set of axes near the top of the graph.
5. Label the x-axis "Distance (mm)" and number it (using equal increments) from 0 to your the value of the location of your last drilling site.
6. Label the y-axis "Depth (mm)" and number it from 0 (the surface) to the maximum thickness of sediment at your coring sites.
7. At site 1 on your graph, mark the thickness of layers beginning at the top (surface) toward the x-axis. Remember to measure the second layer thickness from the bottom of the first layer and so on. Repeat for each site.
8. Draw a line that connects each point at the bottom of layer 1, layer 2, and so on.
9. Color in each of the layers to produce a finished diagram. Compare your results with others from your class.