Shear-wave logs and velocity-porosity relationships in gas hydrates

Author(s): Goldberg, D.; Guerin, Gilles; Meltser, Alex
Ocean Drilling Program, Leg 164, Shipboard Scientific Party, College Station, TX
Author Affiliation(s): Primary:
Lamont-Doherty Earth Observatory, Borehole Research Group, Palisades, NY, United States
Volume Title: American Association of Petroleum Geologists 1997 annual convention
Source: Annual Meeting Expanded Abstracts - American Association of Petroleum Geologists, Vol.6, p.41; American Association of Petroleum Geologists 1997 annual convention, Dallas, TX, April 6-9, 1997. Publisher: American Association of Petroleum Geologists and Society of Economic Paleontologists and Mineralogists, Tulsa, OK, United States. ISSN: 0094-0038 CODEN: APGAB2
Note: In English
Summary: In late 1995, the Ocean Drilling Program acquired downhole log data off the Carolina coast using conventional tools and a dipole sonic tool through natural gas hydrates and gas-saturated sediments. The dipole sonic tool uses a licensed transducer design that was modified to improve signal isolation and conditioning. Our evaluation of the results indicates that the velocity inversion associated with the base of the gas hydrates, which exist over a depth interval of more than 200 m, occurs at approximately 450 m below the sea floor. Vs estimates range between 430 and 700 m/s; however, poor shear wave signals were recorded in intervals associated with free gas. The relationship of Vs with porosity agrees with published models for marine sediments, but their dependence increases in the gas hydrates. The Vp/Vs ratio, which is sensitive to both porous and mechanical sediment properties, decreases from approximately 3.8 to 3.0 over the 150 m interval containing hydrates and possibly indicates a change in their concentration. Shear wave amplitudes are lower in the gas hydrate interval and increase by a factor of 2-4 below. The analysis of seismic data off the Carolina coast implies that gas hydrates are associated with high Vp, low Vs, and anomalous seismic blanking, which is consistent with these log results. These data significantly improve our understanding of the in situ physical properties of gas hydrates since they are unstable under ambient surface conditions and may help to determine their hydrocarbon reservoir potential.
Year of Publication: 1997
Research Program: ODP Ocean Drilling Program
Key Words: 20 Geophysics, Applied; 29 Economic Geology, Energy Sources; Amplitude; Body waves; Elastic waves; Gas hydrates; Geophysical methods; Mechanical properties; Ocean Drilling Program; P-waves; Petroleum; Petroleum exploration; Porosity; Reservoir rocks; S-waves; Sediments; Seismic methods; Seismic waves; Signals; Velocity; Well logs
Record ID: 1997065039
Copyright Information: GeoRef, Copyright 2017 American Geosciences Institute. Reference includes data supplied by American Association of Petroleum Geologists, Tulsa, OK, United States

Similar Items