The invention discloses a method for judging the
fluid type of a reservoir through an acoustic
porosity-
neutron porosity differential, which relates to the technical field of oil and gas
logging, geology and
core test analysis. The method comprises the following steps: 1) accurately calculating shale content, rock compositions, acoustic
porosity and
neutron porosity of the reservoir through core
data calibration logging and
logging data environment correction; 2) excluding the influence of factors such as
lithology, borehole
diameter and mud invasion on an acoustic
transit time and
neutron data; and 3) establishing a standard for judging the
fluid type of the reservoir by comparing the magnitude of the acoustic porosity and the
neutron porosity and using the response difference of the acoustic
transit time and the neutron data to the gas and
formation water. In the method, non-fluid influence factors such as the
lithology, borehole conditions, mud invasion and the like are excluded when the
fluid type of the reservoir is judged, so the characteristics of the influence of different fluids on the acoustic
transit time and the neutron data can be grasped truly, and the
coincidence rate of judging the fluid type of the reservoir is improved from 70 percent currently to over 90 percent.