Study Of The Key Technologies Of Seismic Exploration While Drilling

In recent years, seismic while drilling (SWD) has rapidly developed, as a new downhole seismic technique. It uses the vibrations produced by a drill bit while drilling as a downhole seismic energy source, which makes it belong to passive seismic. Seismic while drilling surveys are acquired without any downhole instrumentation. It means there is no interruption to drilling, no lost rig time and no risk to the borehole while the seismic data are being acquired. These characteristics offer a method by which borehole seismic data can be acquired, processed and interpreted while drilling. Subsurface conditions ahead of the drill bit can be predicted at any time during drilling without tripping out of the hole and seismic data are available at the well site for real-time drill decisions. Furthermore, it can reduce the drilling risk and improve the efficiency of drilling. Therefore, it is very important and necessary to do research on the seismic exploration while drilling.As is known to all, the key technologies of seismic while drilling are very difficult to resolve. So far, there has been not an appropriate method of field acquisition and data processing of seismic exploration while drilling yet. Few companies have gradually tried practice application of the SWD technique at abroad. But there are few researchers to study this technique at home. It has just begun to study seismic while drilling techniques. Then this dissertation aims to research the key technologies of seismic while drilling and it is financially supported by the National High Technology Research and Development Program (863 program) of China (Grant No. 2006AA06A108). Mastery of the technical developments of seismic while drilling at home and abroad, this dissertation analyze the basic principle of seismic while drilling, systematically dissertated and summarized the acquisition method and the data processing of seismic while drilling. In view of the shortcomings of conventional acquisition method of SWD, this dissertation proposes the optimal survey mode and the optimal wavefield separation of SWD. And it is successful to apply these new techniques to the real SWD data acquisition and data processing. By tackling key problems, this dissertation achieves the following breakthrough and innovations:⑴This paper systematically study the SWD wavefield theory and obtain the characteristic of drill-bit wavefield, drill-string wavefield and surface (well site) noise wavefield of SWD. It provides the key theoretical foundation of the optimal survey mode and the optimal wavefield separation of SWD.⑵Based on the characteristic of SWD wavefield, this paper proposes the optimal survey mode of SWD, which settle the key problem of recording the drill-bit signal from the strong ambient noises at well site exactly. By the array of portable seismometer, this survey mode achieve the high- precision, all-day-and-night, long-time, continuous acquisition of real SWD data at home for the first time, which overcomes the shortcomings of traditional method。It not only provides the necessary technical condition for real-time prediction ahead of the drill bit, but also provide an effective approach for long-time energy accumulation。Additionally, this paper proposes that the SWD field acquisition is mainly achieved by seismometers. Conventional land receivers can be used as supplementary sensor. By the optimal survey mode, SWD data of deep vertical well is recorded exactly.⑶Considering the propagation laws of SWD wavefield, this paper proposes the optimal wavefield separation of SWD for the first time, which is based on the characteristics of the SWD wavefield. It resolves the key problem of extracting the drill-bit signal from the strong ambient noises at well site exactly. It is successful to extract the direct arrival from SWD data in G130 well and Ls101 well, by means of the new technique. Also the results can be used for simply predicting ahead of drill bit.⑷Forward modeling of SWD wavefield, drill-bit physical experiment as well as data processing and analyzing of real SWD data, obtain better results. It justifies the validity of this paper proposed optimal survey mode and optimal wavefield separation of SWD and integrates theory with practice.The results and production in this dissertation has instructional meaning and important referenced values for the further study of SWD.