For more than 70 years

surface geochemical exploration technology has been applied in the prediction of deep oil and gas reservoirs through observing anomalous surface expression of hydrocarbon microseepage.It is generally accepted that hydrocarbon may leak from reservoirs through microseepage

but the complex relationship between surface geochemical anomaly and deep hydrocarbon accumulation has not yet been proven.Hydrocarbon microseepage detection in the known oil and gas accumulation in Shiwu faulted depression shows that all of the geochemical indicators in this area are characterized’by heterogeneous geochemical field with low background value

and the concentration of hydrocarbons in the anomalous area is relatively high.The anomalies related to oil and gas accumulation are annular or complex annular while the anomalies caused by a fault or cap rock are banded or block-shaped.The microseepage anomaly in a gas field has different features with that in an oil and gas field.The former is low in intensity and simply annular in shape

while the latter is complicated annular in shape

with some anomalous indicators occurring within the ring.