Abstract：This paper gives an introduction to the 3 well-known formulae (i. e. Wyllie，Raymer and Raiga formulae) which describe the relation between acoustic interval transit time and porosity，and points out that Raiga formula with definite physical significance has wider application. Therefore，the empirical formula for estimating the porosity of argillaceous sandstone with the use of non-linear acoustic porosity model is given by analysing the core samples of mid and deep reservoirs in Songnan X area on the basis of Raiga formula. The practical application results of the formula have been analysed in detail，concluding that the porosities derived from the nonlinear formula are basically identical with the interpretation results of logging data.
