Measurements of attenuation from vertical seismic profiles

Abstract

Values of attenuation have been extracted from five detailed velocity surveys. Significant amounts of attenuation are observed in all five wells. Measured values of attenuation vary by a factor of 10, ranging from less than 0.1 to 0.9 dB/wavelength. Correlation of attenuation with lithology is good, considering the resolution limits of the surveys.One of the surveys was performed in West Texas, and the other four were carried out in the Gulf Coast area. The total number of recording depths in each survey varied from 3 1 to 208, with downhole recordings taken every 10 or 20 ft over key stratigraphic zones. In all five surveys, a monitor geophone was placed near the well to check for source consistency.Two of the better known previous experiments for measuring in-situ attenuation at seismic frequencies were performed by McDonal et al (1958) and Tulles and Reid (1969). These experiments differed from our present surveys in that several geophones were cemented within the boreholes at various depths. Source repeatability was therefore not a problem, and explosive sources were used with frequencies above 400 Hz. Since we were limited to one downhole geophone, we needed sources with repeatable signatures. For the land surveys we used vibrators with frequencies no greater than 80 Hz. We were more fortunate in our offshore experiment, where one of our sources had usable frequencies up to 125 Hz. THEORY NotationOur procedure for measuring attenuation involved constructing the spectral ratio between each downhole pulse and one particular reference pulse. A value of cumulative attenuation (CA) was then extracted from each spectral ratio and plotted as a function of geophone depth. This method allowed us to use many measurements in determining the attenuation over each depth interval.From numerous past experiments we know that the logarithm of the pulse amplitude decays at a rate roughly proportional to frequency. References to many of these experiments can be found in comprehensive articles by Hamilton (1972Hamilton ( , 1976 and Attewell and Ramana (1966). Because of this linear dependence with frequency, we can describe the attenuation process as

Investigation of Preprocessing for Seismic Attenuation Profiling to Image the Earthquake Swarm Associated with the 2000 Eruption of the Miyakejima Volcano in Japan

“…For this study, we assumed that Q is constant over the seismic frequency band, as many previous authors did [7], although Q is frequency-dependent [8]. We calculated the average Q value by using the spectral ratio method, which is a general method for Q estimation [9,10]. The temporal decay in the amplitude of a propagating seismic wave of frequency f from traveltime t1 to traveltime t2 is written as a function of Q: Figure 4.…”

Q as a Lithological/Hydrocarbon Indicator: From Full Waveform Sonic to 3d Surface Seismic

“…Several projects have demonstrated the calculation of Q from seismic transmission data such as VSP (Hauge, 1981), crosswell (Quan and Harris, 1995;Neep et al, 1996), and sonic logging . Very few publications, however, have addressed computing Q from reflection data, and even fewer have published Qvalue estimates from real surface seismic data.…”

Geophysical imaging of subsurface structures in volcanic area by seismic attenuation profiling

“…Although seismic attenuation is well investigated in studies using VSP data (e.g., Hauge 1981;Worthington and Hudson 2000), well log data (e.g., Matsushima 2006) and core samples (e.g., Tompkins and Christensen 2001;Tsuji and Iturrino 2008), it is rarely applied to surface seismic reflection data except previous studies on Open Access *Correspondence: ttsuru0@kaiyodai.ac.jp 1 Academic Assembly, Tokyo University of Marine Science and Technology (TUMSAT), 5-7, Konan 4-chome, Minato-ku, Tokyo 108-8477, Japan Full list of author information is available at the end of the article a direct hydrocarbon indication (Dasgupta and Clark 1998), a fault seal ability evaluation (Tsuru et al 2014) and Q tomography/migration for oil and gas industry (e.g., Zhou et al 2011). …”