Fluid inclusions in the Upper Paleozoic reservoirs in Ordos basin can be classified into 2 types

namely inherited (non-diagenetic) and non-inherited (diagenetic) inclusions

according to their genesis. Based on fluid composition

the latter can be further divided into 3 sub-types

including brine inclusion

CO

2

inclusion and hydrocarbon inclusion. Each inclusion type or sub-type has its own specific geological significance. The reservoirs show two kinds of fluorescence colors. The liquid hydrocarbons in the fluid inclusions show blue and bluish grey fluorescence colors

while the hydrocarbons in the cements show pale yellow and yellowish green fluorescence colors. The former represents the oil feature while it was charged

while the latter represents the results of oil destruction. PVT modeling of liquid hydrocarbon inclusions shows that hydrocarbons would have been charged at relatively high temperature (120℃) and relatively high fluid pressure (38.49 MPa)

which are remarkably higher than the present temperature and pressure in the reservoirs

thus the hydrocarbon properties in the reservoirs have evidently been changed.