Environmental and Exploration Geophysics II

Tom Wilson, Department of Geology and Geography

Environmental and Exploration Geophysics II

[email protected]

Department of Geology and GeographyWest Virginia University

Morgantown, WV

Dipping layer reflection events Dipping layer reflection events and the common midpoint and the common midpoint

gathergather


Dipping Layer Reflection Event with Offset Apex


Vh

Vh

t

tapex2

cos2

0

How do you find depth h, velocity V and dip ?

cos0

t

tapex

0

1cost

tapex


sin2hxapex

sin2apexx

h

If you could not see the direct arrival then you could solve for V using either expressions for t0 or tapex.


This is referred to as a stacking chart. The significance of the name will become apparent later on.


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


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.


Stages of development: Sediments pile up and dip into the Gulf. Mass wasting of the shelf proceeded under the pull of

gravity


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.


http://www.gcmwenergy.com/seismic_line.htm

From Seismic to reservoir image


Seismic acquistion to subsurface imaging

http://www.gcmwenergy.com/seismic_survey.htm


Note the roll-over into the glide zone, synthetic and antithetic faults


http://www.osradp.lsu.edu/downloads/BGBB/4/dome.gif


Complex traps and cap rock


Questions about the Exploration Project

The Main Fault


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)


On Monday we went through the horizon digitization procedures


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


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


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


• 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.

Environmental and Exploration Geophysics II

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Transcript of Environmental and Exploration Geophysics II