Patent ID: 7639563

Claim:
A method for determining the locations of void zones in peripheral casing cement along a borehole by a sonic logging while drilling process, said method comprising: translating a logging while drilling tool, featuring at least one sonic transmitter and a plurality of sonic receivers, within a segment of borehole casing that includes a transition zone from a first diameter casing to a second different diameter casing wherein the casing has been at least partially cemented into place in the transition zone; transmitting sonic signals into the casing; receiving the sonic signals transmitted into the casing at the plurality of receivers of the logging while drilling tool as it translates through the transition zone; and processing the received casing sonic signals to obtain at least one of the attributes of coherent energy and slowness as a function of at least one of depth and time; determining the location of a void zone in casing cement based on a change flag of the at least one of the values of coherent energy and slowness variance.