DISCOVERY BY REFLECTION SEISMOGRAPH 53 
sand, was located in the NW. SW. SW. of Sec. 27. This location was 
chosen because the structure was symmetrical about the road as 
an axis and it was thought wise to locate on the far side of the axis 
from the dry hole in Sec. 28. The Lease Investment Co. well found 
the Taneha sand considerably elevated and with commercial amounts 
of gas and oil, and was completed in this sand. The structural attitude 
of the Pennsylvanian beds and their commercial oil and gas content 
seemed to verify the seismic work, though no reflections as shallow as 
the Taneha were worked, and a south offset location was made in the 
SW. SW. SW. of Sec. 27. This well found the Pennsylvanian beds 10 
feet lower than in the first well, and with some oil, but not enough 
for a commercial well. It was continued on to the Wilcox and was 
completed in this sand for a 4o barrel pumping well. Unfortunately, 
however, the Viola datum on this well was — 2137, which was con- 
siderably lower than had been anticipated. The seismograph data 
were rechecked and found to be entirely satisfactory and convincing, 
as may be seen from the records: shown in Fig. 6. 
Since an oil well in the Wilcox in this area is usually indicative of a 
suitable structure with closure, there was good evidence that the 
geological assumptions from seismic work were in error. In order to 
determine the position of the structure and the reason for the apparent 
inaccuracy of the first map, it was decided to carry out a detailed 
seismic survey of this limited area, employing every means for in- 
creasing our accuracy of depth determination. 
METHOD ADOPTED FOR DETAILED SEISM¥FC SURVEY 
In the second approach to the problem, two factors to increase 
accuracy were stressed. First, it was necessary to eliminate all possible 
small errors in determination of time, such as time break, cap lag or 
surface correction zone determination; and second to survey con- 
tinuously so that small faults or areas of sharp dip were not missed. 
The disadvantage of the former method in determining a depth point 
lay in the necessity of determining such a depth point with only one 
set of conditions in the surface correction zone. To increase the ac- 
curacy of each depth point, it was deemed advisable to secure several 
measurements at or near one point, each determined with different 
surface correction zone conditions. The method adopted was a re- 
finement of a continuous profile scheme used in other detailed field 
problems. Shot points were located 800 feet apart. These holes were 
drilled into the Pennsylvanian shale to a depth of about 50 feet. In 
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