Polynomial amplitude versus azimuth inversion in horizontally transverse isotropic media, as tested on fractured coal seams in the Surat Basin*
Joseph Kremor A E , Randall Taylor B and Khalid Amrouch C DA Woodside Energy Ltd., 240 St Georges Terrace, Perth, WA 6000, Australia.
B Origin Energy Ltd., 339 Coronation Drive, Milton, Qld 4064, Australia.
C Australian School of Petroleum, University of Adelaide, North Terrace, SA 5005, Australia.
D Centre for Tectonics Resources and Exploration (TRaX), Department of Physical Sciences, University of Adelaide, Adelaide, SA 5005, Australia.
E Corresponding author. Email: joseph.kremor@woodside.com.au
The APPEA Journal 57(2) 776-780 https://doi.org/10.1071/AJ16239
Accepted: 28 March 2017 Published: 29 May 2017
Abstract
A new technique of amplitude versus azimuth (AVAZ) seismic inversion in horizontally transverse isotropic (HTI) media is presented. AVAZ is an effective method of characterising anisotropic variation within individual reflectors as well as characterising fractures. The compressional wave reflectivity equation in HTI media has been reformulated into a parabolic form that allows for fast and efficient inversion. The isotropic component of the azimuthal reflectivity has been separated precisely from the anisotropic component and the anisotropic component has been decoupled exactly into its constituent elliptic and anelliptic components. The exact isotropic, elliptic and anelliptic amplitude versus offset (AVO) gradient equations in HTI media are presented herein and the amount of error associated with previous approximations is also defined under the assumption of weak anisotropy. A method of calculating Thomsen’s weak anisotropy parameters using these AVO gradient terms is then outlined. Compared with the elliptic method, there is reduced error incorporated in the new AVAZ method and the error relationships of this method are compared with the Fourier method.
Data from an open file 3D wide azimuth seismic survey in the Surat Basin were inverted to demonstrate the effectiveness of the techniques which are presented herein. Seismic amplitudes from six azimuthal stacks were extracted over two horizons and inverted around a well where full-wave sonic and density logs were acquired. For both horizons, the error between the inverted anisotropy parameters from seismic and the inverted anisotropy parameters from wire line logs were found to be less than 5% for both horizons.
Keywords: anisotropy, AVAZ, AVO, cracks, fractures, seismic, WAZ.
Joseph Kremor has been a graduate data scientist at Woodside Energy Ltd since 2016. Prior to joining Woodside, Joseph graduated first in his class from the University of Adelaide in Petroleum Geology and Geophysics and completed internships at Origin Energy. Joseph holds degrees in mathematics and geological science from the University of Queensland and is a recipient of the Geological Society of Australia’s Gold Medal. What is presented here formed part of Joseph’s undergraduate thesis. |
Randall Taylor is a seismic interpreter and QI geophysicist. As chief geophysicist for Origin Energy, Randall is responsible for the application of geophysical technology and functional assurance to Origin’s Australian and international exploration and production portfolio. Randall holds a BAppSc in geophysics from the University of Queensland (1982). Randall transferred to Origin Energy in 2000 after 6 years with Oil Co. of Australia as team leader in the Otway and Eromanga basins. Prior to this, Randall was senior geophysicist for Santos Ltd (1987–92) in their offshore group. Randall began his career in geophysics with CSR’s Oil and Gas Division. Randall is a member of several industry bodies, including ASEG, SEG and PESA. In 2001, Randall served as special editor of the ASEG journal Exploration Geophysics. |
Khalid Amrouch is a structural geologist with expertise in geomechanics. He graduated from the University of Pierre and Marie Curie (Paris) with an MSc and a PhD in structural geology. His main interest relates to brittle tectonics, fracture characterisation and 4D stress analyses. Khalid started his career in 2005 at the Institut Français du Pétrole (IFP), which sponsored his studies, followed in 2010 by a position as research engineer at Mines PariTech. In 2012, Khalid spent 1 year working for BHP as an exploration geologist in Chile, before joining the Australian School of Petroleum in February 2013. Since then, Khalid has been an active member of the S3 Research Group, one of the largest geoscience research groups at the University of Adelaide. |
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