Sound Wave, Full Wave Logging Information Processing Research

The full-wave acoustic logging signals include the information of velocity, amplitude, frequency and waveform envelope characteristics of longitudinal wave, shear wave, Stoneley wave and so on. Through digital signal processing, the information of longitudinal wave, shear wave and Stoneley wave can be obtained. Then we can be flexible to carry out just as stratum elastic properties, fracture pressure, formation permeability, fracture and evaluation, which can expand the sonic logging in the oil exploration. But the signals not only mix with the noise, but the emergence and superposition of new components of full-wave acoustic signals (that is, each component signal superposition) is not a jump but a smooth transition process. For these reasons, a lot of methods have not worked in actual use. Therefore in order to effectively isolating the various components of full-wave logging signals, and getting the information of layer properties as well as more clearly reflection of underground geological conditions, it is necessary to be processed before in application of full-wave acoustic logging signals. Against the characteristics of component of full-wave acoustic logging signals and the various restrictions of traditional methods of signal processing, and through in-depth research and analysis, the signal processing methods based on wavelet denoising and instantaneous frequency analysis can accurately and effectively obtain the first wave of the acoustic components on the timeline.The full-wave acoustic logging signals of typical dry layer, water layer, and gas layer in some well of the South China Sea oil block are processed and analyzed with the proposed method, respectively the signal processing of monopole and dipole mode. First, the full-wave acoustic logging signal is processed with denoising wavelet analysis, as well as selecting db5 and heursure threshold imposition ways. Then, the full-wave acoustic logging signal in which the noise is removed is processed with instantaneous frequency analysis, using the phase difference method based on the central finite difference (CFD). The discontinuous point in the signal phase information that is the location of the first wave of acoustic components is obtained with phase derivation. The noise has been very well removed using the above proposed method. The instantaneous frequency signal waveform shape is the same as before de-noising. Furthermore the first wave locations on the timeline of longitudinal wave, shear wave, Stoneley wave can be clearly identified. The parameters of reflection underground geology such as slowness can be calculated after obtained the first wave of location.Compared the slowness with foreign professional software, the slowness with above proposed new method can be seen not only similar at characteristic points and curves but also more smooth. Combination with conventional well log analysis, it can be well evaluated the actual layer formation. That means the slowness curve with new method is reliable. Then that means the new method can accurately and effectively extract the location of the first wave of components full-wave acoustic logging signal.