The invention discloses a method for judging the
reservoir fluid type of a difference between density
porosity and
neutron porosity and relates to the technical fields of oil and gas
logging and geology and
core test analysis. The method comprises the following steps: 1) accurately calculating the shale content, the rock composition, the density
porosity and the
neutron porosity of a reservoir bycore data calibrating
logging and
logging data environmental correction; 2) removing the influence of factors of
lithology, well
diameter and mud invasion on density and
neutron data; and 3) establishing standards for judging the
reservoir fluid type by utilizing the response difference of the density and the neutron data to gas and
formation water and by comparing the values of the density porosity and the
neutron porosity. When the invention judges the
reservoir fluid type by utilizing the density and the neutron data, non-fluid influencing factors, such as
lithology, borehole conditions, mud invasion and the like are removed, therefore, influence features of different fluids to the density and the neutron data can be truly reflected, and the
coincidence rate for judging the reservoir
fluid type can be enhanced to above 90 percent from the existing 70 percent.