Abstract:

In a basinwith pressure compartments，true interval velocity of layers beyond the reach ofdrilling can not be obtained by using velocity spectrum when the velocities obtained from velocity spectrum in the pressure compartments are very different from themeasured velocities during drilling（for example sonic logging）.In this case，the interval velocity of deep layers beyond the reach of drilling can be extrapolated based on“pressure compartmentmodel”.The basic formula for extrapolation can be expressed as the functional relation between formation pressurewithin the pressure compartments and interval velocity.First，the theoretical interval velocity of the first layer beneath the bottom hole is calculated by using the functional relation，and then the theoretical interval velocity of the second layer beneath the first layer is calculated，and the rest can be obtained in the samemanner.

Key words: interval velocity, velocity spectrum, pressure compartment, formation pressure, extrapolation, deep layer