Engineering Geology Homework
You can solve this problem in teams of two (2) students, or if you prefer you could do it alone.
Deliverables:
- Short report explaining your solution (2 pages max.)
- Interpreted seismic lines
Read all the attachments provided. If you need more information you should do some research.
Attachments:
- Deformation
- The Four Stages of Seismic Exploration
- Keywords
- Seismic line (Color, 1)
- Seismic line (B&W, 1)
- Stratigraphic Column
- Geological XSection
Case Study: Oil and Gas Exploration in the Weald
This case study is set in the southeast of England in a basin known as the Weald.
Find the oil - an interpretation exercise -
This is an exercise to locate any structural features on the seismic data that could act as trap for hydrocarbons. Working geophysicists called interpreters do this on seismic data all the time.
1) A seismic profile was shot from South to North, with the low CMP numbers in the South. A borehole was drilled on this seismic line at CMP 740 and from this we know the lithology and stratigraphic sequence at that location. Geophysical measurements taken down this borehole allow us to link the horizons on the seismic section to the real lithology. This is called the well tie.
2) Using the results of the well tie, we can identify the following horizons and rock units:
|
Horizon
|
Rock Type
|
|
Trough at 424ms
|
Purbeck Sandstone
|
|
Peak at 710ms
|
Kimmeridge Clay
|
|
Zero crossing positive to negative at
959ms
|
Corallian Limestone
|
Using this information we are now ready to interpret the seismic profile.
3) Locate the well tie position on the top of the seismic section, and directly under that point mark the time of the horizons specified in the well tie using a different coloured pencil for each one. The very black events are peaks, the greyer ones troughs and zero crossings are white.
4) Taking one horizon at a time, follow the peak or trough across the whole section (it may be easier to use a lead pencil to mark your progress). A zero crossing is the changeover point from either a peak to a trough (positive to negative), or a trough to a peak (negative to positive). The horizon may not be continuous all the way across the profile. Try to think about possible structures to explain any jumps or breaks in the horizon, (faults for example). Remember if you think you see a break that could be a fault, you should see a similar break in the horizons above and below. When you are confident you can see where the horizon goes, colour it with your chosen colour.
5) Mark any faults on the section with a lead pencil. Try to describe it, e.g. it is a normal/reverse fault, downthrow side to the north/south, throw approximately xxms.
6) Finally when you have traced all the horizons and marked any faults, look at the whole picture and answer the following questions:
Can you see any dipping horizons or structures?
Where might there be an accumulation of oil or gas?
How would it have got there?
Attachment:- Assignment Files.rar