Borehole Compensated Sonic tools determine the time required for a compressional sound wave to travel through one foot of formation. The travel time depends upon the formation's lithology, porosity, and type of pore fluid. Thus, if lithology and type of pore fluid are known, travel time can be related to porosity.
As an aid to interpretation of seismic data, the compressional travel times are integrated and the results indicated on the log. A tick mark appears on the log for each millisecond of elapsed time. The interval between tick marks indicates the depth interval through which sonic waves travel in 1 millisecond.
Compensated Sonic tools contain two acoustic transmitters and two acoustic receivers. The standard arrangement of these components results in travel time measurements made with transmitter-to-receiver spacing of 3 and 5 feet. The use of such multiple travel time measurements allows for compensation for borehole fluids, borehole rugosity, and tool tilt
Compensated Sonic tools are run in liquid-filled wells and should be centralized in the borehole. The tools can be combined with other tools such as Gamma Ray, Induction, Laterolog, Density, Neutron, and Caliper.