1. Environmental and Exploration Geophysics II tom.h.wilson wilson@geo.wvu.edu Department of Geology and Geography West Virginia University Morgantown, WV Introduction to the Seismic Exploration Project

2. Exam will cover elementary reflection and refraction seismology including 1) 2-layer reflection and refraction analysis, 2) 3 layer refraction analysis 3) forward and reverse refraction profiling (single layer) 4) energy loss mechanisms and energy partitioning

3. Normal Incidence Seismic Profile Shot point locations TwowaytraveltimeTwowaytraveltime

4. The exploration project area is located in the foreland of the Appalachian Mountains

5. Faults in the basement play an important role in controlling the location of hydrocarbon reservoirs.

6. Distribution of sediments in the basement cover with interval velocities and traveltimes.

7. Reversal of fault motion can be observed throughout the regions. The example below comes from one of the lines to the north.

8. These synthetics indicate that reflections from the top and base of the reservoir interval are mixed in with reflections from surrounding intervals, but coincide with the negative cycle observed at about 0.31 seconds.

9. The synthetic seismogram mentioned earlier can be used to provide a detailed view of individual reflection events and their relationship to the detailed stratigraphic features in the reservoir and surrounding intervals.

10. Prominent reflection events have been identified in this slice of seismic traces.

11. This line courses through the field from its southeastern to northeastern extents. Line 6 from your handout

12. This seismic profile crosses the Rome trough and reveals several basement faults

13. The correlation of reflections to subsurface stratigraphic intervals is made using synthetic seismograms compiled from well data obtained near a seismic profile. We’ll talk more about synthetics in the weeks to come.

15. Interpretation of major reflection events observed in the foregoing seismic section

19. This seismic profile crosses the Rome trough and reveals several basement faults

20. Note that layer 1 thickens over the trough indicating that the trough was subsiding during the deposition of those sediments. Layer 4 however, thins out across the trough indicating that the floor of the trough must have been uplifted during the deposition of that layer of sediment

21. When we examine various regions within this area we see that that faulting of the basement surface was not confined to a single episode of deformation but continued through time.

22. Note the subtle thickening and thinning of the section across the line.

23. We can plot the reflection events in a relative rather than absolute depth scale to enhance some of these subtle structures.

25. This map of the basement faults beneath the area was compiled from seismic data. The fault to the east or left in this map marks the east margin of the Rome trough. The fault to the west drops down into the trough interior.

26. In this seismic section you can see that to the left in the deeper part of the section reflectors drop down to the left, but rise to the left in the shallower part of the section. Downward movement along the fault evident in this section reversed later in time. Later in the history of the area basement block on the left moved upwards.

27. Again note the east margin of the trough and the second step out.

28. In this display, line 6 has been reversed, so that the northwest end is off to the right. Note the general structural style and the reversal of movement that occurred later in the history of the area elevating the shallower strata to the northwest.

29. This map shows the variation of travel time from a shallower reflector to the Big Injun. Note that during that through the more productive northern part of the field, travel times are less, implying in this case that the interval has thinned.

30. In this map the subsidence trends at various times in the past are plotted relative to areas of high cumulative production.

32. In this area we see that a series of basement faults formed early in the history of the basin.

33. As time passed (Ordovician to Pennsylvanian) we see that minor movements along these deeper structures created subtle patterns of thickening and thinning in deposited strata.

34. We also infer the presence of late stage detachment resulting from compression forces associated with plate collision during the formation of the Appalachian Mountains. In addition, it appears that movement along the deeper basement faults may have continued after the episode of folding.

35. 4.1 is due today Read pages 144-170 and 191-197 Prepare paragraph outlines of your term report and hand in on Tuesday (October 15th). Prepare 3 paper summaries - no due date; papers are out in the mail room Each exploration group should get together and pick a Big Injun well. Each individual in the group should write up a paragraph discussion explaining the rationale behind their choice.

36. There will be a test next Thursday. Bring questions about the test to class next Tuesday - in Lab.