Geophysical extraction of subsurface parameters using seismic while drilling (swd) technique for formation evaluation

The geophysical extraction of subsurface parameters using seismic while drilling (SWD) technique for formation evaluation, specifically encompasses the seismic techniques operated while the drill string is lowered in the borehole, during effective drilling, during manoeuvres or while connecting drill pipes. The seismic-while-drilling (SWD) is an improved geophysical methodology that utilisesthe vibration produced by the drilling bit to obtain, in real time, geological information ahead of the bit and around the well. This technique has been used steadily since 1986. The drill-string reverberations disturb the seismic signals obtained by correlating pilot and geophone measurements because the pilot waves are reflected at each interface between string sections with different acoustic impedances. Inverse filtering of these reflections, using a reference-pilot deconvolution calculated in the presence of additional noise, may cause signal distortion. To overcome this problem, we consider using dual-sensor measurements in the drill string to remove the reflections of the drill-bit waves in the acquisition phase and to improve pilot deconvolution. Numerical modelling of seismic wave propagation in realistic complex geological structures is an important tool for the planning of 3D (SWD) experiments. These data are used to optimise the seismic line geometry, to assist the signal and noise recognition, and to understand the nature of the different events (wave conversion, diffraction, multiples, etc.) for interpretation, imaging purposes and used to improve the SWD seismograms.