Page 165 - Geochemical Remote Sensing of The Sub-Surface

142 V.T. Jones, M.D. Matthews and D.M. Richers

,,,,,
Geochemical Methods of
Prospecting and Exploration
I
I I
[ Direct t ! I Indi,ootl
I ! I
i
:i_1
,
H;drochemical I Soil-Salt J Microbiological !
--~Free soil 'gases .] ~ Fluorescence ]
~ Marine survey] method
Surface core [
-~ Gas logging ] Deep cores I U w to, wo. -q.o no I
I seismic shot holes __~ Chloride ]
oroox --. I woH,og g 1 Formation brines [ [-Gypsum I

....
-~ Water classification i

Fig. 5-6. Geochemical methods of prospecting for petroleum and natural gas (reproduced with
permission from Kartsev et ai., 1959, Geochemical Methods of Prospecting and Exploration for
Petroleum and Natural Gas, copyright by the University of California Press).

oxygen isotopes (Donovan et al., 1974); and many other effects as reviewed by
Matthews (1985).
As an exploration tool, the identification of hydrocarbon seeps is particularly useful
when coupled with remotely-sensed images and photographs. Case studies by
researchers in the West have shown that secondary indicators of microseepage are often
present in the near-surface environment. Examples noted by Horvitz (1972), Donovan
(1974), Donovan and Dalziel (1977), Matthews (1985) and Ferguson (1975) have
indicated the presence of diagenetic alteration of soils above or adjacent to hydrocarbon
accumulations. Work by Rock (1985), Matthews et al. (1984) and Patton and Manwaring
(1984) has shown that these effects may often be reflected in the health and type of
vegetation over the seep, which also alters the spectral response detected by satellite and
airborne sensors. These methods of geochemical prospecting for oil and gas are
reviewed in more detail in Chapter 7.
Others have noted changes in resistivity or radioactive signatures above
accumulations due to the seepage and possible interaction of ascending fluids and
solutions with the encapsulating medium. In some cases the actual removal or addition
of soluble chemical species has been noted.