Abstract: The method for calculating gas saturation based on fluid factor f which was proposed by Russell could be used for gas-bearing evaluation of unconsolidated sandstone reservoirs. Dipole shear sonic imager (DSI) logging could measure P-wave and S-wave velocity accurately in unconsolidated sandstone, and calculate the fluid factor f, combined with conventional logging data. This paper proposes a method of adjustable parameters for unconsolidated sandstone, which could improve the evaluation capacity of the fluid factor f to reservoir fluid. The result of in situ data processing and interpretation is good in agreement with the gas test results in Sanhu Area of Qaidam Basin, and it shows the method of gas-bearing evaluation based on f could improve the accuracy of interpretation in unconsolidated sandstone reservoi

Key words: fluid factor, unconsolidated sandstone, dipole shear sonic imager logging, P-wave and S-wave, gas-bearing evaluation