Study On Slowness Estimation And Wave Field Separation Method For Stoneley-wave Of Array Acoustic Logging

Stoneley wave is an effective mean to evaluate reservoir permeability and fractures in carbonate rock .The energy decay of Stoneley wave is decided by natural attenuation of borehole and formation and pore connectivity ,therefore it reflects formation permeability directly .There are many methods and technologies to calculate interval transit time ,but some problems exist in selecting window and finding peak. Based on the global optimization characteristics of immunity genetic algorithm and the principle of slowness calculating with slowness time coherence, a new integrated processing technique of array acoustic data is proposed with slowness time coherence and immunity genetic algorithm in the paper. The correlation function reflecting waveform similarity in slowness time coherence is used as the object function of immunity genetic algorithm, then, maximum of object function is found with immunity genetic algorithm, finally the wave arrival time and slowness values corresponding to the maximum value of object function are gotten. The integrated method is not affected by the steps of wave arrival time and slowness, and global optimization solution is found with less computation in the range of given slowness and wave arrival time. Crossed multiple array acoustic data processing for five wells in Daqing Oil Field is done, and the result is compared with that of commercial software eXpress, and good agreement has been achieved. It shows the proposed method can be applied to slowness estimation of array acoustic data with good accuracy.In order to evaluate formation permeability with Stoneley wave , wave separation must be done. Based on different characters of Stoneley wave frequency phase and velocity firstly , Stoneley wave is abstracted with a Fourier domain filter, then ,a median filter is used to obtain direct Stoneley wave ,and frequency-wavenumber difital filter is used to separate the upgoing and downgoing reflected Stoneley-wave sections.The center frequency and reflectivity of Stoneley-wave is calculated with separated Stoneley waves. The processing result is compared with that of commercial software eXpress,and good agreement has been achieved .It shows the proposed method can be applied in Stoneley wave separation.