Page 180 - Geochemical Remote Sensing of The Sub-Surface

Light hydrocarbons for petroleum and gas prospecting 15 7

4 -
!
0
= 3

< 2 - I I
7-
W
0 IOO0 20OO
Meters
Fig. 5-14. Variations in methane concentration in air above a petroleum reservoir (from Antropov,
1981).

CH4, x 10"4%
6-

4- O
O
~ .....j o to
I
I
~ 0 ~.~,,.~ I 0
_o/
2- I

0 i .... i..I...l ,1 I .1 . f ---
10 12 14 16 18 20 22
T~e, hr

Fig. 5-15. Variations in methane concentration in air as a result of seismic shock to the ground
(from Antropov, 198 ! ).

not exist that the gases being detected by the sensor are low molecular-weight
hydrocarbons and nothing else", he has published numerous positive case studies
relating the response of one of these instruments to soil gas probe anomalies (Burson and
Thompson, 1985). Additional technical difficulties result from the fact that microwave
adsorption energy levels represent rotational energy in the molecule. Deactivation of
rotational energy by collisions can occur rapidly at atmospheric pressure, causing the
molecule excited by the microwave energy to lose its adsorbed energy in a non-emission
mode, thus reducing the signal-to-noise ratio. This coupled with the low concentrations
of hydrocarbons in the atmosphere has meant that the technique has not been extensively
tested as an exploration tool.