The intercept time method was introduced in the early sixties for the computation of static corrections, when multiple coverage became a usual recording technique. This method gives the slowness of the refractor and the delay time at the shot and receiver positions. These delay times are related to the thickness and velocity of the altered zone. This paper presents a stand alone method for the computation of the formation acoustic slowness and of the delay times from full waveform acoustic data recorded with a multi-receiver tool. The paper also shows examples of slowness and delay logs derived from acoustic data recorded in both a sandstone reservoir and a carbonate reservoir. The delays are borehole consistent and correlated to the lithology. On the first example of a reservoir consisting of share and sandstone, the delay time increases in shaly zones. In the sandstone porous zones, the increase of the delay time is related to the presence of unconsolidated sands. The second field example is a carbonate reservoir consisting of dolomite with a few limestone layers. In this reservoir, the delay time increases are related to fissured or fractured zones and, the comparison of the porosity and of the altered zone extension can help to discriminate the zones of secondary porosity from fissured zones.