Page 242 - Geochemical Remote Sensing of The Sub-Surface

Gas geochemistry surveys for petroleum 215

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DETECTION TECHNIQUES AND INSTRUMENTATION

iNDICATORS AND PARAMETERS

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iDIAPIRISM AN] ICLINE LITitOLOGY FAUI.T PALEO- [ THRUSTS ttYDRO-
CON F'ORMITY MORPitO LOG Y DYNA MIC
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SHALLOW BIOGENIC GAS COALBED GAS THERMAL GAS OVER MATURED GAS

Fig. 6-2. l:actors that intlucnce surthcc gcochelnical patterns of hydrocarbons.

Whilst the execution of such surveys calls for appropriate methods of sampling and
sufficiently sensitive analytical techniques, the planning and interpretation stages require
a conceptual model to guide thinking. The model must be consistent with the principles
of petroleum geology and geochemistry and provide a strategy for undertaking the
survey and a reasonable explanation of the results. Since the very beginning of gas
geochemical surveys, various models have been proposed; Price (1986) has given a
critical review of the literature and proposed a working model which stresses the
importance of surface conditions. Probably there will never be a perfect model, because
there are so many interrelated factors influencing the relation between surface anomalies
and their underlying oil and gas fields (Fig. 6-2).