Application Of Correlation Technology In Seismic While Drilling

Seismic while drilling is a new technology which developed in the early 90's of the 20th century. It uses the vibrations produced by a drill bit while drilling as a downhole seismic energy source. There are many different ways in seismic while drilling. but together, they often use the method in practice relies mainly acceleration sensor which installed at the top of the drill string to receive signal as an approximate bit signal, and then through the cross-correlation processing between the reference signal and the ground detector records, seismic profiles can be got. This method is simple, practical, low cost, does not affect the drilling operation. However, seismic data while drilling is seriously affected by the strong surface noise and drill string propagation. If by noise removal, deconvolution processing can improve the signal to noise ratio of seismic data while drilling, it can be able to predict the construction details of the stratum ahead of the bit.Cross-correlation is a core part of the seismic data while drilling processing, although this method is not the only way, but it is the most reliable and most widely used method. In this paper, based on previous studies dealing with the correlation of seismic drilling methods, further research and new cross-correlation methods are explored.The essence of seismic while drilling cross-correlation algorithm is to get a seismic profile which make autocorrelation of bit signal to be a wavelet. The correlation technology of the seismic while drilling in this paper mainly includes reference signal autocorrelation and the cross-correlation between reference signal and the ground detector signal. The former is used to detect the cyclical component in the reference signal, decay unrelated elements with the time-varying, extract bit signals and calculate delay time of drill string through the drill string multiple wave to provide accurate data for the follow-up time delay of the cross-correlation profile The cross-correlation between the reference single and the ground detector records is mainly to compress continuous bit signal into equivalent record excited by point source and enhance signal to noise ratio through keeping the common signal and noise and attenuate non-coherent noise between the cross-correlation traces.In this paper, three-component seismic while drilling data have been processed through cross-correlation technology and some cognition is got based on the processing with p-wave.Cross-correlation peak is not completely compressed sharp pulse in traditional cross-correlation profile. The results have a certain width of the side lobe. In this paper, seismic while drilling method is improved by the third-order statistics method, because it can completely suppress the affect of Gaussian noise in field data collection. In the received formation response profile, Peak is more narrow, side-lobe suppression is more thorough, and processing effect is better. The third-order statistics method can suppress Gaussian noise in the maximum extent. It can better describe the characteristics of the reference signal through third-order statistics diagonal slice. For the traditional method of the second-order statistics, which is commonly used cross-correlation method, it is a good improvement.