Gas geochemistry surveys for petroleum

The consequences of these developments in China were that petroleum companies, geological institutions and the Sinica Academy carried out a series of gas geochemistry research programmes on land in areas with different climate conditions and offshore. This chapter outlines the background, some of the methods that were developed and illustrates some of the results. 

Surface macroseeps of oil and gas, which can be seen by the naked eye, led to the discovery of some of the most famous oil fields in the world (Link, 1952). Today, almost all of the visible macroseeps have been tested and drilled. Microseeps are the extension of macroseeps into the non-visible range. Their detection therefore requires the use of alternative methods, most obviously gas geochemical surveys. 

VEGETATIO CLIMATE SOIL POLLUTION THICKNESS MORPHOLOGY 1 

FAULTS POROUS ROCKS IMPERMEAB UYERS SOURCE ROCK HYDRO- GEOLOGY FISSRES 

SHALLOW BIOGENIC GAS COALHEU CAS THERMAL CAS OVER MATURED GAS 

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Soil samples are usually collected at the surface proper or at depths of up to several metres below the surface. As far as possible, samples are kept in their original condition until they are prepared for analysis in the laboratory. The analytical procedures are invariably partial extraction techniques. This approach has been widely used in other branches of exploration geochemistry, but assumes particular importance in gas geochemical surveys for petroleum. 

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