APPLICATION OF THE INTERCEPT TIME METHOD TO FULL-WAVE-FORM ACOUSTIC DATA

The intercept time method was introduced in the early sixties for the computation of static corrections, when multiple coverage became a usu al recording technique. This method gives the slowness of the refracto r and the delay time at the shot and receiver positions. These delay t imes are related to the thickness and velocity of the altered zone. Th is paper presents a stand alone method for the computation of the form ation acoustic slowness and of the delay times from full waveform acou stic data recorded with a multi-receiver tool. The paper also shows ex amples of slowness and delay logs derived from acoustic data recorded in both a sandstone reservoir and a carbonate reservoir. The delays ar e borehole consistent and correlated to the lithology. On the first ex ample 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 dolom ite with a few limestone layers. In this reservoir, the delay time inc reases are related to fissured or fractured zones and, the comparison of the porosity and of the altered zone extension can help to discrimi nate the zones of secondary porosity from fissured zones.