SBIR-STTR Award

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. Calculatin 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.Anticipated Results/Potential Commercial Applications as described by the awardee:This method, if successful, will particularly interest the oil and gas and geothermal industries. It will provide VSPs and acoustical impedance data in wells where instruments cannot be placed. This in turn will provide geophysical data for wells whose hole diameters or temperatures restrict the use of downhole instruments.

Vertical seismic profiles (VSPs) are used to makemore accurate interpretations of seismic reflection data and to provide seismic images beyond the limits of the wellbore. In this project, the drill bit will be used as a seismic source to derive an inverse vertical seismic profile (IVSP). Using this method, the driller can look ahead of the drill bit to determine any impending problems caused by changes in geology that could break bits or cause blowouts. The method uses the autocorrelation function to compress the random pulses produced by a drill bit into an equivalent individual source pulse and the autocorrelation of the earth's transmission response. According to the Kunetz-Claerbout relationship, the resulting autocorrelogram is equivalent to a pseudoreflection seismogram. The autocorrelation method of obtaining an IVSP has several advantages over current technology. First, the top of the drill string does not need to be monitored simultaneously to obtain a pilot signal. Also, better resolution and signal-to-noise levels can be obtained because there are no restrictions on the amount of data that can be collected and stacked to produce the pseudoreflection seismogram. In Phase I, finite difference computer models and actual field data were used to verify the mathematical theory. Unlike the models, the field data contained periodic cultural noise. Filtering methods were developed in Phase I to remove this noise. In Phase II, additional filtering methods will be evaluated, on-site processing developed, and three field monitoring projects performed.Anticipated Results/Potential Commercial Applications as described by the awardee:This IVSP method would be of particular interest to the oil and gas and geothermal industries. It would also be of interest to the DOE in its drilling and logging projects that are associated with the National Petroleum Reserve, Nevada Test Site, and waste disposal programs. The technique would provide VSP and acoustical impedance data in wells where instruments cannot be placed. These data in turn would provide geophysical data for wells whose hole diameters or temperatures restrict the use of this method would provide vital use of down-hole instruments. More importantly, information while drilling.