DISCLAIMERThe submitted manuscript has been authored by a contractor of the U.S. Government under contract No. W-31-1WENG-38. Accordingly, the U. S. Government retains a nonexclusive, royalty.free licensn to pvblish or reproduce the published form of this contribution. or allow others to do so, for U. S. Government purposes.This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recorn- ABSTRACTVelocity and attenuation data were used to test theoretical equations describing the frequency dependence of compressional wave velocity and attenuation through gas-rich sediments in coastal Louisiana. The cross-well data (obtained from a variable-frequency, cross-well seismic experiment using source frequencies of 1, 3, 5, and 7 kHz) were augmented with velocities derived from a nearby seismic refraction station using a lowfrequency (QO Hz) source. Velocities obtained h m the borehole-sonic tool (18 kHz)were not used, because it is unclear at this time what signal phase was being detected. Energy at 1 and 3 kJ3z was successfully transmitted over distances from 3.69 to 30 m; the 5-and 7-lcHz data were obtained only at distances up to 20 m.Velocity tomograms were constructed for one borehole pair and covered a depth interval of 10-50 m. Results from the tomographic modeling indicate that gas-induced low velocities are present to depths of greater than 4-0 m. Analysis of the velocity dispersion suggests that gas-bubble resonance must be greater than 7 kHz, which is above the range of frequencies used in the experiment. Washout of the boreholes at depths above 15 m resulted in a degassed zone containing velocities higher than those indicated in both nearby reitaction and reflection surveys. Velocity and attenuation information were obtained for a low-velocity zone centered at a depth of approximately 18 m. Measured attenuations of 1.57,2.95, and 3.24 dB/m for the 3-, 5-, and 7-m~ signals, respectively, were modeled along with the velocity data using a silt-clay sediment type, Density and porosity data for the model were obtained from the geophysical logs; the bulk and shear moduli were estimated from published relationships. Modeling results indicate that gas bubbles measuring 1 mm in diameter occupy at least 25% to 35% of the pore space.

The submitted manuscript has been authored by a contractor of the U.S. Government under contract No. W-31-1WENG-38. Accordingly, the U. S. Government retains a nonexclusive, royalty.free licensn to pvblish or reproduce the published form of this contribution. or allow others to do so, for U. S. Government purposes. This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recornmendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof. * This work was supported by the Gas Research Institute, Chicago, Illinois, through contract 5088-252-1770 with DISCLAIMER Portions of this document may be illegible in electronic image products. Images are produced from the best available original document.