For the Shaximiao Formation reservoirs in western Sichuan

both the concentration indexes(such as the methane

propane and heavy hydrocarbon of headspace analysis

the methane

propane and heavy hydrocarbon of acidolysis-hydrocarbon analysis

and the fluorescence 320 nm and 360 nm) and the ratio indexes(such as headspace humidity coefficient

headspace propane/methane

acidolysis hydrocarbon humidity coefficient

acidolysis hydrocarbon propane/methane

and fluorescence 360 nm/320 nm and 405 nm/320 nm)

are obviously higher than that in Penglaizhen Formation reservoirs.Decrease or positive gradient of hydrocarbon concentrations are noticeable

suggesting that hydrocarbon vertical micro-migration do occur.The 3D fluorescence spectrum of natural gas in Shaximiao Fm reservoirs has apparent T

2

peak

the pattern of which is relatively complex and is remarkably different with that in Penglaizhen Fm reservoirs.Based on graph theory

fuzzy cluster

factor analysis

nonlinear mapping and correspondence analysis

the reservoir rocks in Penglaizhen and Shaximiao Formations can be divided into two types.They have a good natural grouping features and identifiabiliity.Discriminant model built on Fisher Criteria demonstrates that the function of headspace methane is the largest

indicating that headspace methane is very important in identifying gas reservoirs in the well by geochemical prospecting.