Determination of in situ attenuation from full waveform acoustic logs

Abstract

Methods for the determination of in situ P and S wave attenuation from full waveform acoustic logs are developed. For P waves, the peak amplitude ratios of the refracted P waves from two different receivers can be used with geometrical spreading taken into account. For S waves, owing to the contamination by the guided waves, its attenuation cannot be determined directly. Instead, S wave attenuation is determined from the attenuation of the guided waves using the partition coefficients (normalized partial derivatives of the phase velocity with respect to the body wave velocities). Analytical forms of these partition coefficients are presented here, along with examples for a number of different rock formations (granite, limestone, sandstone and soft sediments). The results show that in high velocity rocks, the fluid attenuation controls the guided wave attenuation except near the cutoff frequency of the pseudo‐Rayleigh wave. For low velocity rock formations, especially in the case where the S wave velocity is lower than the fluid velocity, the S wave attenuation is the main contributor to the guided wave attenuation. Synthetic microseigmogram calculated with the measured body wave attenuation agrees well with the actual microseismograms.

Sonic waveform attenuation in gas hydrate‐bearing sediments from the Mallik 2L‐38 research well, Mackenzie Delta, Canada

“…where w 0 is the source central frequency and j is the unit imaginary complex number [Cheng et al, 1982]. The source function is simplified by an exponentially decaying sinusoid.…”

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

“…This equation can also be found in Toksoz et al (1979) and Cheng et al (1982), in a slightly different form. In these two papers, M 1 and M 2 denote the amplitudes of the seismic waves from a common source measured at distances z 1 and z 2 , respectively.…”

“…Since the early 1980s, many researchers have attempted to develop techniques for the inversion of Q P from singlehole full waveform acoustic log data; in particular, to obtain depth profiles of intrinsic Q P P -1 from the head P wave of the sonic data. In a popular approach, Q -1 P P is calculated from the Amplitude Spectral Ratio (ASR) of the head P wave measured at two locations (e.g., Cheng et al, 1982;Sun et al, 2000;Dasios et al, 2004). In this approach, the borehole head wave is analogous to a plane wave in a uniform unbounded medium.…”

Karakteristik Gelombang Stoneley dalam Menentukan Permeabilitas Reservoir Sumur Pemboran

“…Dari data mentah gelombang, secara diskrit di cari atenuasi dan frequensi gelombang Stoneley dari masing-masing input data dengan pencuplikan menggunakan fiter hamming window. Sedangkan perhitungan faktor atenuasinya diperoleh dengan menggunakan metoda spektrumdivision [12] dan untuk menghitung frequensi gelombangnya dengan metoda centroid frequensi [13].…”