ANALYSIS OF SURFACE GEOCHEMICAL CHARACTERISTICSOVER TYPICAL GAS POOL——TAKE XIAOQUAN-XINCHANG GAS FIELD IN THE SICHUAN BASIN AS AN EXAMPLE

By analyzing relations between surface geochemical indicators and deep gas pool in Xiaoquan-Xinchang gas field of the Sichuan Basin,one can obviously obtain that large numbers of surface geochemical tracks from deep gas accumulations is closely response to the types and scales of deep gas accumulations.Using geochemical detecting methods,one can catch these micro-traces,thus providing deep gas accumulations exploration with reliable basis.The anomaly shape of acid hydrocarbon,ΔC,heat-released hydrocarbon and micro magnetism is mainly annular or spotted.Head-space gas is a good indicator to deep gas accumulations.It is characterized by concentration changing greatly over gas accumulation and changing little out of gas accumulation.Microbiological indicator is corresponding to deep gas accumulation.Methane oxidation bacteria have annular or spotted anomaly features.Sulfate-reducing bacteria show a character of top anomaly.For reducing risk of prediction and increasing rate of success in gas exploration,it is needed to combine surface geochemical indicators with geologic setting.