Processing of Monopole Compressional In Slow Formation Available to Purchase

Slowness time coherence (STC) processing (Kimball and Marzetta, 1984), is a robust and reliable technique to obtain the slowness of the formation from an array of sonic waveforms. The processing is robust automatic and provides easy evaluation of arrivals across an array of sonic waveforms. Nevertheless, in some instances, if the wave propagation is complex, the usual evaluation procedures used in the processing may lead to erroneous results. An example is very slow formations, in which the compressional wave can be as slow as, or even slower than, the mud in the borehole. In this case, the main component of the monopole waveforms is a borehole mode, dispersive, which propagates at the mud slowness. The compressional head wave vanishes because the energy is refracted away. Under these circumstances, when using conventional procedures, the compressional slowness log reads the mud slowness in slow intervals. Therefore, improved processing to extract the compressional slowness of the formation is required. In this paper a methodology is presented to obtain the compressional slowness of a slow formation. The first part of this processing consists of correcting the dispersion of the borehole mode to obtain the low-frequency asymptote corresponding to the compressional slowness of the formation. Simultaneously, the waveforms are filtered using an optimal bandpass filter, which is based on a sensitivity analysis. Examples involving actual datasets demonstrate the efficiency of the new processing.