Hexxon
Oil & Gas exploration corporation
Dr. Geo Physicist, PhD.
Hexxon Oil & Gas Exploration Corp.
561 Canal Street
Placerville, CA 95667
Jr. Geophysicists
Hexxon Oil & Gas Exploration Corp.
561 Canal Street, Room E151
Placerville, CA 95667
Re: Your Career as a Geophysicist
1/20/01
Dear Employee:
I am the corporate president in charge of Hexxon Oil & Gas Exploration
Corporation. We are currently interested in the prospect of major underground oil and gas reserves in an area located offshore in the Gulf of Mexico. We have just discovered that our competitor, Smell Oil & Gas has been gathering geophysical seismic data in that same area.
Background Information.
Geophysical seismic data is the information that scientists/geophysicists use to predict the geologic formations that exist underneath the
Earth’s surface. Seismic sound waves are generated on top of the Earth’s surface with dynamite, big “thumper” trucks, air guns, etc. The sound waves travel through the Earth, reflect off rock layers, and bounce back. Instruments, called geophones on the Earth’s surface, record the sound waves. Geophones are small amplifiers. They work just like your stereo’s amplifiers or a stethoscope that amplifies the sound of your heartbeat.
Scientists record and process the data. They take each recording and change that longitudinal wave into a wiggle trace that has peaks and troughs as if it were a transverse wave. Huge computers take all this information and make a picture of the rock layers underneath the Earth’s surface. The image is recorded as a two-dimensional crosssection, which is called a “Seismic Cross-Section.” Each seismic cross-section displays all the sound waves with the location of the signal source (on the ground) on the x- axis, and two-way time on the y-axis.
The Problem.
The Board of Directors is alarmed at the potential loss of their investment if Smell drills a well and discovers oil first. This could mean millions of
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dollars lost if they beat us to the oil reserves. Therefore, you and your team of geophysicists have been sequestered until a potential drilling site has been agreed upon.
We MUST drill a well before Smell Oil & Gas beats Hexxon to these potential reserves that are estimated at 50 million barrels of oil and 3 trillion cubic feet of gas.
The data that you are about to utilize is TOP SECRET! It MUST remain within this room. You have only two days to work together with your team to map these prospects. The third day will be spent presenting your findings to the entire group.
Procedure – Familiarize yourself. To get started, the first thing you should do is getting oriented with your map and seismic lines. Each seismic line has been designated with the letters D, H, Y, and Z. Compare the lines to where they are located on the map.
Highlight the location of each line on the map. It is very important that you learn to think in “3-D,” and comparing the map locations of lines D, H, Y, and Z to the map will help you do this. Fold each seismic line and tape them together in the same order: D, Z, H, Y.
Just put tape on the tops and bottoms of the pages.
The seismic information is easy to understand. Look at the numbers across the top of each seismic section. These numbers represent each location where the sound waves were generated. They are called shot points because they correspond to the locations of where the truck was vibrating the Earth, or where the dynamite was “shot” off. For example, see if you can find shot point #1468 on seismic line Y. Now see if you can find the same shot point on the map. If you cannot find these two points, NOW is the time to ask for help!!!!!!!
Incorporation of Well Information.
Now that you are familiar with the seismic data, the well information should be matched to the seismic line. Oil & gas wells that have been drilled in the past are great sources of information that scientists may use for
“interpreting” the seismic data and predicting where oil & gas might be found in other locations. The well control point that you have is named after the landowner, Joe Blow
#1. The #1 means that this is the first well drilled on property belonging to Mr. Joe
Blow. The well can be found on seismic line Y at the shot point #1468. Compare the well location on the seismic line to the same location on the map. Draw and label the name of the well on the map as well as on the seismic line.
Having this well gives us a great deal of information about the area that we hope to prospect for oil and gas. For example, we know the rock formation in the well has gas at a depth shown as 340 ms on the seismic cross-section. Mark this layer on seismic cross-section Y with an orange colored pencil. Also, mark the layer that is directly below it at 450 ms on the well. Color this layer blue. Now, try to connect these two horizons from seismic line Y to Z, H and D by coloring the trough all the way around the loop from line Y to Z, H, and D. If you can fold the entire “loop” and the rock formation connects between lines D and Z, then you be confident that you correlated the rock layers correctly. Congratulations! You are now a junior geophysicist!
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Rock correlation.
When evaluating the well-named Joe Blow #1, geologists discovered oil at a depth shown at 1600 ms (see overhead). This rock layer is known as the Dolly Madison formation and can hold millions of barrels of oil, if we can just find it!
The trough at 1600 ms marks the top of the gas zone. This will be the third formation you will try to “correlate” (connect around the loop), D, Z, H, Y. Color this horizon the color green.
There is also another oil producing zone at 1490 ms (see overhead projector).
You should mark this horizon on your seismic line to help you correlate around the loop.
This will be the fourth horizon that you want color a fourth color when trying to map it.
Feel free to use any other distinguishing layers that can help you connect the troughs.
Try to map the formation by following these two horizons around the loop.
Connect line Y to H, Z, and D. Don’t forget, if you lose your horizon, then maybe you should put in faults (breaks in the Earth’s crust that move a rock formation/layer up or down), so you can correlate the oil-bearing horizon from one line to the next. If you can get around the loop and back again, then you have earned the dubious distinction of
Junior Geophysicist. If you cannot get around the loop of seismic data comfortably, then maybe you should erase an area and start again. Hint: Don’t color too dark so you can erase! Remember, changing your mind is part of the job of “interpretation.”
Mapping the Dolly Madison.
Now try to make a map of the Dolly Madison formation. Mark any faults that cut only the green rock layer called the Dolly Madison.
See if you can connect these faults from one seismic line to the next. Hint: faults trend northeast to southwest.
Try to make a map of the two-way times for this layer. Mark depths at every shot point (places on map that have the loction numbered) all the way around your loop. You might want to pick extra points to document the times to the shallowest depths of the layer, deepest depths of the layer or any other points that show something changing in the rock layer – edges of the faults, etc. Remember, it’s called a seismic “interpretation,” for good reason!
Now, contour the map by connecting points of equal value. The contour interval is 10 milliseconds so you should have a contour for 1550, 1560, 1570, 1580, 1590, and
1600.
Thank you for your attention to this matter. I am looking forward to seeing your results when you present them at the next Board of Directors’ meeting in two days.
Should you have any questions or concerns, please contact me at (530) 622-3634 (ext
1151).
Sincerely,
Dr. Geo Physicist,
PhD
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