Estimation of Azimuthal Anisotropy from VSP Data Using Multicomponent Velocity Analysis

Abstract

Observation of azimuthal shear wave anisotropy can be useful for characterisation of fractures or stress field. Shear wave anisotropy is often estimated by measuring splitting of individual shear-wave events on VSP data; however this method may become unreliable for zero-offset (marine) VSP where the seismogram often contains no strong individual shear events but many low-amplitude PS conversions. In this paper we introduce a new approach to estimation of fast and slow shear wave velocities and orientation of polarization planes based on the multi-component velocity analysis. This technique is applicable to zero-offset VSP data and should take advantage of the presence of a large number of shear wave events with the same velocity. The main idea is to estimate the velocity for a given polarization direction by measuring the coherency of the seismic signal of a large number of events as a function of the apparent velocity. The algorithm was tested on marine 3C VSP acquired in the NorthWest Shelf of Australia. These tests show good agreement between anisotropy parameters (magnitude and orientation) derived from the VSP and cross-dipole sonic log data.

Applicability of Zero-offset and Offset VSP for Time-lapse monitoring – CO2CRC Otway Project Case Study

“…Existence of strong shear wave anisotropy in Otway basin first time was reported by Turner and Hearn in 1995. Recently we have suggested an approach for multi-component velocity analysis of 3C zero-offset VSP data [Pevzner et al, 2009]. The method was Barcelona, Spain, 14 -17 June 2010 tested on data from Naylor-1 and CRC-1 acquired earlier and showed similar anisotropy parameters for both boreholes, also they corresponds to orientation of regional stress field.…”

Spatial variation in azimuthal anisotropy due to sand-shale distribution: Stybarrow Field case study

“…Up to 15-20% difference in fast and slow velocities are observed in the dipole shear logs (Figure 1). Further evidence has been observed in borehole breakout data, VSP data (Pevzner et al, 2009) and 3D seismic migration velocities (Hung et al, 2006;Bishop et al, 2010). The fast velocity direction (125°/305°) observed in the velocity data also approximately matches the maximum regional stress direction (Hillis and Reynolds, 2000).…”

Reinterpretacja tektoniki w obszarze Pomorza Zachodniego w oparciu o nową wersję profilu sejsmicznego 2D po reprocessingu

“…4). Ze względu na fakt, że pionowe profilowania sejsmiczne PPS zawierają informację o anizotropii prędkości (Grechka et al, 2007;Pevzner et al, 2009) zastosowanie modelu prędkości uzyskanego z danych PPS dało bardzo dobre efekty w przypadku migracji czasowej po składaniu dla profilu sejsmicznego z rejonu Karpat (Bajewski et al, 2017a). Szczegółowy opis budowy pola prędkości na potrzeby migracji czasowej po składaniu przy użyciu pionowych profilowań sejsmicznych został opisany w pracy statutowej Bajewskiego et al (2018b).…”