Curtin/CSIRO Geophysics Group Seminar, 24th June 2021

P-wave anisotropy parameters estimation from multi-well 3D VSP data acquired with geophones and DAS at Otway Site

Date: Thursday, 24 June, 2021
Time: 10:00 AM – 11:00 AM
Location: ARRC Seminar Room, 26 Dick Perry Avenue, Kensington
Presenter: Sofya Popik, PhD student, Exploration Geophysics, Curtin University
Authors: S. Popik, R. Pevzner, A. Bona & B. Gurevich

The quality and accuracy of a seismic image can be significantly affected by anisotropy. When anisotropy is significant, neglecting it can lead to smearing of the image, dispositioning of reflections and distortion of amplitudes. Thus, it is imperative to estimate anisotropy and take it into account, especially for long-offset or wide-azimuthal seismic data.

This study estimates P-wave anisotropy parameters at the Otway site (Victoria, Australia). A wide range of available offsets acquired within the CO2CRC Otway Project provides a unique opportunity for anisotropy estimation from 3D vertical seismic profile (VSP) data. Possibility to permanently install DAS cable in the wells and obtain 3D VSP data for the entire depth brought a number of benefits to the monitoring program. In this study we estimate P-wave anisotropy from direct wave arrivals in VSP data acquired with geophones in two wells and distributed acoustic sensors (DAS) installed in five wells.

Data analysis reveals seismic anisotropy of the subsurface with a significant presence of both polar and azimuthal anisotropy. We estimate key parameters such as normal moveout velocity, azimuthal ellipticity, polar anellipticity and fast-velocity azimuth by nonlinear fitting of the analytical travel time approximation to observed direct P-wave travel times from 3D VSP data. Obtained anisotropy parameters show that polar anellipticity remains almost constant and equal to 0.1 for the whole depth range, while azimuthal anisotropy changes significantly with depth: it is relatively weak in the shallow section then increases significantly below a depth of 600 m. The fast-velocity azimuth coincides with the orientation of the maximum horizontal stress in the study area. The results show that despite their low sensitivity for large offsets, the DAS receivers provide sufficient information on anisotropic travel times over the entire length of the well, which is critical for reflection imaging from both VSP and surface seismic data.

Sofya Popik is a PhD candidate in Exploration Geophysics at Curtin University, Australia. Sofya completed her BSc and MSc degrees (2011-2017) in Geophysics at Lomonosov Moscow State University, Russia. She has two years of seismic processing experience for oil and gas projects with GeoPrime LLC (Moscow, Russia).

Sofya’s PhD is a part of the CO2CRC Otway Project. Her PhD focuses on integration of borehole and surface seismic monitoring techniques in CO2 geosequestration projects with the main focus on anisotropic velocity model building for improved characterization of subsurface. In her PhD Sofya works with innovative technologies such as 4D (time-lapse) surface and borehole seismic and fibre-optic distributed acoustic sensing (DAS)