Transcript No Slide Title

Environmental and Exploration Geophysics II
Dipping layer reflection events and the
common midpoint gather
tom.h.wilson
[email protected]
Department of Geology and Geography
West Virginia University
Morgantown, WV
Tom Wilson, Department of Geology and Geography
Dipping Layer Reflection Event
with Offset Apex
Tom Wilson, Department of Geology and Geography
How do you find depth h, velocity V and dip ?
tapex
t0

tapex
t0
2h cos 
2h
V
V
 cos 
1 tapex 
  
cos 
 t0 
Tom Wilson, Department of Geology and Geography
xapex  2h sin
h
xapex
2 sin 
If you could not see the direct arrival
then you could solve for V using either
expressions for t0 or tapex.
Tom Wilson, Department of Geology and Geography
Tom Wilson, Department of Geology and Geography
Tom Wilson, Department of Geology and Geography
Tom Wilson, Department of Geology and Geography
Tom Wilson, Department of Geology and Geography
This is referred to as a stacking chart. The significance
of the name will become apparent later on.
Tom Wilson, Department of Geology and Geography
For next week at this time construct a
stacking chart for a symmetrical split spread
consisting of 12 geophones arranged 6 on
each side of the source.
Bring questions to class on Tuesday
Tom Wilson, Department of Geology and Geography
Tom Wilson, Department of Geology and Geography
Tom Wilson, Department of Geology and Geography
Tom Wilson, Department of Geology and Geography
Tom Wilson, Department of Geology and Geography
Tom Wilson, Department of Geology and Geography
Tom Wilson, Department of Geology and Geography
Tom Wilson, Department of Geology and Geography
Tom Wilson, Department of Geology and Geography
The effect of the moveout correction on the traces in the common midpoint
(CMP) gather is to create a composite normal incidence trace that effectively
shares a coincident source and receiver at the midpoint shared by all the traces
in the gather. We’ll discuss CMP data in more detail in a couple lectures.
Tom Wilson, Department of Geology and Geography
Stages of development: Sediments pile up and dip into the Gulf.
Mass wasting of the shelf proceeded under the pull of gravity
Tom Wilson, Department of Geology and Geography
Faults rise to the surface in the landward direction as the
sediments take a sled ride into the Gulf. These faults
accommodate extension at a slow (creeping) but steady
pace. Time is always available in excess for the geologist.
Tom Wilson, Department of Geology and Geography
From Seismic to reservoir image
http://www.gcmwenergy.com/seismic_line.htm
Tom Wilson, Department of Geology and Geography
Seismic acquistion to subsurface imaging
http://www.gcmwenergy.com/seismic_survey.htm
Tom Wilson, Department of Geology and Geography
Note the roll-over into the glide zone,
synthetic and antithetic faults
Tom Wilson, Department of Geology and Geography
Tom Wilson, Department of Geology and Geography
http://www.osradp.lsu.edu/downloads/BGBB/4/dome.gif
Tom Wilson, Department of Geology and Geography
Complex traps and cap rock
Tom Wilson, Department of Geology and Geography
Questions about the Exploration Project
The Main Fault
Tom Wilson, Department of Geology and Geography
At a minimum you should have digitized the main
(synthetic fault – light blue) and the antithetic fault that
cuts back into the main fault (antithetic fault- light green)
Tom Wilson, Department of Geology and Geography
On Monday we went through the horizon
digitization procedures
Tom Wilson, Department of Geology and Geography
Just as with the fault your picks can be displayed in map view
by double clicking the horizon or by dragging over the
Amplitudes or Times from the horizon list in the project tree
Project tree
Tom Wilson, Department of Geology and Geography
For the remainder of the class work in pairs as
you complete your horizon interpretation
Note the presence of fault
gaps in your horizon picks.
This is where you will draw
in a fault polygon.
The gap at left is produced
by the intersection of the
main synthetic fault with the
interpreted horizon
Tom Wilson, Department of Geology and Geography
Fault Gap
We’re running a little bit behind but I think we need to take the time
to be sure you have the basics down. So we will conclude this
exercise next Monday
Tom Wilson, Department of Geology and Geography
• Construct a stacking chart for a symmetrical split spread consisting of 12
geophones arranged 6 on each side of the source (see handout).
Bring questions to class next Monday. Chart is due next Wednesday.
•Complete your reading of Chapter 4. Dipping layer reflection events are
covered on pages 183-186, with additional discussion on pages 186-196.
The idea of common depth point sorting is discussed on pages 225 -229.
We’ve talked tangentially about resolution (217-219) and velocity analysis
(233-238). We will be talking about stacking of CDP gathers (238- 241)
and migration (241-244). Discussions of migration will come later but it is
helpful to be aware of the issues early on.
• Look over problems 4.1, 4.4 and 4.8.
Tom Wilson, Department of Geology and Geography