The Study Of Inversion Method About First-arrival Time In Array Waveform

The derivation of accurate acoustic head wave arrival time is very important in oilfield borehole logging. We can use the information to analyze the detection depth and velocity which is used in geophysics exploration. It also can be used in the borehole stable analysis to know the damage region. In addition, first-arrival time can be used to detect fluid invasion and to know the formation around the borehole. The most difficult thing to realize this technology is to improve the accuracy of the outcome data and computational speed. So we should do our best to solve them.Firstly, we discuss the characteristics of wave propagation in thin bedded formation and altered formation using the finite difference theory. Then we analyze the reasons of the slowness change in these formations from the theory angle. After these, we discuss the common technology to get the first-arrival time, such as threshold detection, STC and f-k coherence filtering method. And analyze the advantages and disadvantages of these methods. Then we applied these methods in the field data and compare the results. At the same time, we explain the reasons of the slowness changes in thin bedded formation. So we propose a new method to derive the high- resolution slowness and apply it into real data. The results show that this method can improve the resolution of the slowness. Besides, this method can get the reliable results without human being’s intervene in the given well. At the same time, this method can provide monitoring parameters to help users know the well condition. Finally, we propose another method to get the high precision slowness and put it into real data. And the results are also reliable.