Environmental and Exploration Geophysics II

Environmental and Exploration Geophysics II Dipping layer reflection events and the common midpoint gather tom.h.wilson tom.wilson@mail.wvu.edu 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 ? Tom Wilson, Department of Geology and Geography

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

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

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

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

Homework • 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

Environmental and Exploration Geophysics II