VERTICAL SEISMIC PROFILING WHILE DRILLING

VERTICAL SEISMIC PROFILES (VSPS) PROVIDE INFORMATION FOR MORE PRECISELY INTERPRETING INTO GEOPHYSICAL SEISMIC DATA, AS WELL AS GEOPHYSICAL INFORMATION BEYOND THE LIMITS OF THE WELLBORE. THE HIGH DEGREE OF REDUNDANCY NECESSARY TO ACQUIRE THIS TYPE OF DATA, AND THE COMPLICATIONS THAT CAN ARISE FROM PLACING GEOPHONES DOWN A BOREHOLE MAKE DATA ACQUISITION EXPENSIVE AND TEDIOUS. THIS PROJECT INVOLVES USING THE SEISMIC SIGNAL PRODUCED BY A DRILL BIT DURING DRILLING AS A SEISMIC SOURCE. THE DATA ARE RECORDED AT THE SURFACE ON AN ARRAY OF GEOPHONES. COMPUTER PROCESSING OF THE RECORDED DRILL BIT SIGNAL COMPRESSES THE INDIVIDUAL SOURCE PULSES PRODUCED BY THE BIT INTO THE AUTOCORRELATION OF THE TRANSMISSION SEISMOGRAM. THIS AUTOCORRELATION IS EQUIVALENT TO THE REFLECTION SEISMOGRAM. INVERSION TECHNIQUES ARE AVAILABLE TO PRODUCE AN ACOUSTICAL IMPEDANCE MODEL FROM THE RESULTING PSEUDO-REFLECTION SEISMOGRAM. CALCULATING THE AUTOCORRELATION FUNCTION FROM DATA ACQUIRED AT SEVERAL DEPTHS IN THE WELL MAY ALLOW COMPILATION OF A VSP. BY COLLECTING THIS TYPE OF DATA DURING DRILLING, THE GEOPHYSICIST CAN LOOK AHEAD OF THE BIT TO WARN THE DRILLER AGAINST ENTERING POTENTIALLY DANGEROUS, OVERPRESSURIZED FORMATIONS. USING THE DRILL BIT AS A SEISMIC SOURCE REDUCES THE COST AND ENVIRONMENTAL DAMAGE THAT MAY OCCUR USING TRADITIONAL TECHNIQUES. DATA CAN BE ACQUIRED WITHOUT INTERFERING WITH DRILLING.