Reference Signal Anaysis Of Seismic While Drilling

Seismic while drilling technology is a new borehole seismic technology whichwas developed abroad in the early1990s. The drill-bit vibration,which is used to be asource, is recorded in the detectors on the ground and derrick.After apre-processing,the signal from ground sensor does cross-correlation with the one frompilot sensor to obtain the single shot record of SWD which is similar with that ofvibroseis seismic prospecting. The travel time of direct wave and reflected wave isused to get the propagation velocity of the wave and drill location in a variety offormations and to predict the depth of the front destionation, details of stratumstructure and formation lithology. Compared with conventional VSP and surfaceseismic, seismic while drilling technology has its own characteristics and uniqueadvantages, such as synchronization with the drilling process, lower developmentcosts, little risk of instrument and less demand on the environment. The target the oilworkers strive to is accurate,efficient and safe drilling. Seismic while drillingtechnology has tremendous potential and it has become more sophisticated in foreigncountries. However, the core technology is mainly in the hands of a few largecompanies who do not sell to China. At present SWD in china is still in its infancy,focusing on the exploratory research of theory and methods that exits a large gap withinternational standards.So it is important to research SWD theories and technology.The paper discuss the SWD basic theory on the basis of VSP and inverseVSP,which have following contents:(1) Focusing on the analysis of the signal characteristics of cone bit,a kind ofrotary drilling, it is a detaied study and summary on the formation mechanism andpropagation characteristics of SWD wave. The analysis of SWD direct wave andreflected wave provides the theoretical basis for its recognition in the seismic profile.(2) There are four methords to receive the drill-bit signals. In this paper, thechange of the reference signal is discussed which is obtained in the three experimentsincluding forward modeling, indoor percussion signal physics experiment and SWD physics experment. If there is no wellsite noise, the various types of waves aresuperposed on each other in the pilot sensor. Drillstring wave field is complex, whichis seriously affected by multiples. Based on the study of the indoor SWD experiment,the paper obtained that high and low frequency interference can cause the drill signalphase reverse(3) There is a detailed discussion of the unilateral and bilateral deconvolutionmethod which are applied in the data processing of G130. It can eliminate thetransmission effect of the drill string and impress SWD data quality.