Obtaining arrival times of seismic signals at a borehole receiver using a reference wavelet measured at a shallower depth

摘要

In a method of VSP seismic surveying a source generates a first seismic signal which is measured at a receiver on a bottomhole assembly at a first depth. The first depth may be a shallow depth. The received signal, which may be a direct arrival received within ten seconds of transmission of the first seismic signal, is used to determine 411 a reference signal (e.g. reference wavelet). The reference signal measured at the one depth of the BHA is used for processing of signals at the next greater depth in order to determine the arrival time. The process can be repeated 409 at subsequent depths, updating the reference wavelet at each depth. The method can also be used with a seismic source in another preexisting wellbore (i.e. crosswell measurements). Also disclosed is a method of sending coded information about the source signal to the downhole tool. The coded information is used to reconstruct the source waveform and process the VSP data.