Tom Wilson, Department of Geology and Geography Environmental and Exploration Geophysics II tom.h.wilson Department of Geology and Geography West Virginia University Morgantown, WV Moveout and Coincident Source-Receiver Concepts & 3D Seismic Interpretation

Tom Wilson, Department of Geology and Geography Here is some shot data collected in Marshall Co. WV We’d like to turn this into geology. Why do the amplitudes drop off below 200ms? Enhanced display How do we get here?

Tom Wilson, Department of Geology and Geography The effective source receiver geometry for the records shown at right across the east margin of the Rome Trough is corrected so that the source and receivers share the same surface location. But - this is not the way the data was collected. The short story

Tom Wilson, Department of Geology and Geography Note that the reflection point coverage spans half the distance between the source and receiver

Tom Wilson, Department of Geology and Geography The split spread provides symmetrical coverage about the source

Tom Wilson, Department of Geology and Geography Moveout and the moveout correction

Tom Wilson, Department of Geology and Geography Redefine the reflection time equal to the 0-offset arrival time (t 0 ) plus the  t (drop from t 0 or “moveout”).

Tom Wilson, Department of Geology and Geography  t is the normal moveout correction Assume  t 2 is small relative to other terms and can be ignored to approximate the moveout

Tom Wilson, Department of Geology and Geography Look at the reflection time distance relationship in terms of t 2 versus x 2 Square both sides of this equation

Tom Wilson, Department of Geology and Geography The hyperbola becomes a straight line

Tom Wilson, Department of Geology and Geography In the t 2 -x 2 form, the slope is 1/V 2

Tom Wilson, Department of Geology and Geography V is derived from the slope of the reflection event as portrayed in the t 2 -x 2 plot. The derived velocity is referred to as the Normal Moveout Velocity, NMO velocity, or, just V NMO. The moveout velocity

Tom Wilson, Department of Geology and Geography The V NMO is used as a correction velocity If the velocity is accurately determined the corrected time  equals t 0

Tom Wilson, Department of Geology and Geography Fun with hyperbolas and ellipses

Tom Wilson, Department of Geology and Geography If the correction velocity (V NMO ) is too high then the correction is too small and we still have a hyperbola

Tom Wilson, Department of Geology and Geography And we have

Tom Wilson, Department of Geology and Geography

NMO correction of the reflection events appearing in the shot records across relatively horizontal strata yields a more accurate image of subsurface geology.

Tom Wilson, Department of Geology and Geography

These data sets are referred to as being single fold data. Single fold implies only one trace per mid-point. Single fold data are also sometimes referred to as 100% data

Tom Wilson, Department of Geology and Geography Sediments shed from the uplifted Sierra Madre Mountains pile up in coastal areas of the Rio Grande Embayment. The pull of gravity on this large mass of sediments caused faults to develop that accommodated gradual sliding or creep of large sediment laden blocks out into the Gulf of Mexico. Gulf Coast Play

Tom Wilson, Department of Geology and Geography Deltas load the shelf with sediments and gravity takes over

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 We don’t have an exact duplicate of the style of deformation we see in the 3D seismic for your exploration project, but you can see some of the elements in the seismic shown here.

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 The Barrel Data

Tom Wilson, Department of Geology and Geography CRETACEOUS Sotbakken Gp Torsk Fm Nygrunnen Gp KVITING FM Adventdalen Gp KOLMULE FM Kolje Fm Knurr Fm Hekkingen Fm FUGLEN FM Kapp Toscana Gp ST FM 7122 well to the southwest

Tom Wilson, Department of Geology and Geography 7224 well to the northeast

Tom Wilson, Department of Geology and Geography Suggested interpretation is Triassic

Tom Wilson, Department of Geology and Geography Triassic? Cretaceous? Do they tie?

Tom Wilson, Department of Geology and Geography Triassic? Cretaceous?

Tom Wilson, Department of Geology and Geography

 Continue your reading > Chapter 4, pages 165 to 199 and 206 to 229. Problem sets 3 and 4 are due next Monday

Tom Wilson, Department of Geology and Geography Time to do some 3D seismic Interpretation Bring up Kingdom Suite