used to demonstrate the close relationship between seismic reflections and de- 

 flections of the interval velocity curve on the CVL log. Figure 21-15 shows an 

 interesting comparison of reflection response to velocity contrasts. The illustra- 

 tion reveals that good seismic reflections are obtained from a given horizon in 

 certain instances but are not obtained in other instances in the same local area. 

 The velocity log of Well No. 2 (right) shows a sharp velocity contrast at the 

 top of the "Mississippi lime." The corresponding position on the seismic record 

 obtained at the well reveals the presence of a good quality reflection. The 

 velocity log of Well No. 1 (left) shows only a gradational velocity contrast at 

 the "Mississippi lime." The corresponding position on the seismic record fails 

 to reveal the presence of a recognizable reflection. Therefore, the conclusion 

 is warranted that changes in quality and character of a particular reflection may 

 be correlative with changes in stratigraphic conditions. Increased shale content 

 of sands or limestones, or the local appearance of increased porosity, should 

 affect reflection response. 



The close relationship between seismic reflections and abrupt deflections of 

 the velocity curve is shown in Figure 21-16 and 21-17. It is observed in Figure 

 21-16 that reflections are associated with both increase in velocity, as at the 

 Navarro and Austin, and decrease in velocity, as at "C" horizon and at the Cow 

 Creek. The section between the Georgetown and Cow Creek shows high interval 

 velocities, and the corresponding shortening of time interval on the seismic 

 record is well illustrated by the convergence of the correlations below the Austin. 



A seismic reflection record synthesized in the laboratory from the velocity 

 log, along with the actual field seismic record obtained at the well, is shown in 

 Figure 21-17. The reflection character correlation between the two seismic 

 records is good. A synthetic reflection record can be prepared from any velocity 

 log. Its application to seismic exploration work can be invaluable since it can 

 solve many difficult reflection identification problems. In addition, the synthetic 

 record may furnish the yardstick by which the reflection record quality of a 

 contemplated seismic exploration program can be measured. The velocity log 

 then may be used as a partial substitute for an experimental program from 

 which the standards of reflection response in an area are obtained and by which 

 instrumental techniques or adjustments effected to insure reflection records of 

 optimum quality. 



Velocity Logs Faithfully Reproduce Formation Characteristics 



The features shown in Figures 21-9 through 21-15 demonstrate that the 

 velocity response affords reliable correlative character at different wells separat- 

 ed both by long and by short distances. Figures 21-18 and 21-19 furnish added 

 proof that the CVL log portrays detailed formation characteristics accurately. 

 Logs run at different times in the same well are shown in Figure 21-18. The 



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