Sound speed and attenuation measurements in gassy sediments in the Gulf of Mexico

Abstract

The speed and attenuation of sound in gassy marine sediments in the Mississippi delta area have been measured by means of small (1 to 500 mg) explosive charges buried 30 m below the mud line. The respective values obtained were 800 m/sec and 1.4 dB/kHz-m. Effective gas content was estimated to be approximately 0.06 percent.

Significance of hydrocarbon seepage relative to petroleum generation and entrapment

“…Gas clouds, gas chimneys, bright spots, pull downs, wipe outs, gas disturbed zones, and blank-out zones are well described in the literature (Sweet, 1973;Anderson and Hampton, 1980;Siddiquie et al, 1981;Edrington and Calloway, 1984;Abrams, 1992). Many geophysicists consider these features as seismic noise that degrades the quality of seismic reflections.…”

Q measurements from compressional seismic waves in unconsolidated sediments

“…The arrangement was made possible by the known lateral homogeneity of the unconsolidated sediments at the Wendover site. This experiment was part of a Sandia program to develop a gun-launched, instrumented, sea-bed penetrator system which could emplace payloads at depths of at least 50 m in soft marine sediments (Edrington and Calloway, 1984). Data collected by the system by means of acoustic pulses generated from small explosive charges would then provide information on the propagation properties of the medium under consideration.…”

Preliminary mapping of void fractions and sound speeds in gassy marine sediments from subbottom profiles

“…(equal to the ratio of the specific heats of the gas, divided by the polytropic coefficient 7,10,12 ), which is assumed to be 1.3 for nearly adiabatic pulsations of biogenic sedimentary gas. 9 The void fraction being small, ␤ Ӷ 1, means that the bubbly sediment can be treated as an effective fluid medium of density eff , where eff (1) to the data in Fig. 2(a) allows estimation of the vertically averaged void fraction between the top of the seabed and layer 1 ͑␤ s−1 ͒, and the vertically averaged void fraction between layer 1 and layer 2 ͑␤ 1-2 ͒.…”

“…1) or be inverted to estimate the bubble population. Bubble radii distributions from 10 µm to 20 mm, and void fractions as great as 9%, have been inferred from the inversion of either compressional wave data, [6][7][8][9][10] acoustic backscatter, [11][12][13] or two-frequency techniques. [14][15][16] While such inversions can be based on models of bubbles in water, a model incorporating geotechnical properties of the host sediment surrounding the bubbles (both before and after it is altered by the presence of bubbles) would be preferable.…”