In order to reveal the link between the physical mechanism of identifying gas and water zones in igneous rock with longitudinal and transverse waves

'

velocity

and the internal factors of reservoirs

and guide the identification of fluid types in igneous rock

the Carboniferous igneous rock core of the Junggar Basin was selected

and its longitudinal and transverse waves

'

velocities were measured via the ultrasonic pulse method . The longitudinal and transverse waves

'

velocities of the core in the dry state and the water-saturated state were obta

ined. In addition

the influence of the internal factors of reservoirs like the fluid types

porosity

density and lithology on elastic wave velocity were analyzed. The research showed that the gas-bearing state of the formation would cause the significant decrease in both the longitudinal wave velocity and the ratio of longitudinal to transversal wave velocities

but had a small impact on transversal wave velocity. In formations with low porosity

it was difficult to identify the fluid types because the difference in the characteristics of the longitudinal and transverse waves

'

velocities in gas and water zones was weakened. Due to the complex lithology in igneous rock and the great influence of SiO

2

content on elastic wave velocity

fluid types should be identified by different lithology. Based on the above conclusion and in order to highlight logging responses of fluids

V

P

/

V

s

-

R

t

crossplots were established by different lithology to identify gas and water zones in tested formations in the research area. For intermediate-basic rock and acid rock

the

V

p

/

V

s

values are 1.85 and 1.75

respectively

which can be used to distinguish the gas zone and the water zones effectively; however

due to the influence of low porosity

it is difficult to effectively distinguish between the gas zone and the gas-water coexistence zone.