Anisotropy parameter inversion from sonic and density logs in horizontally transverse isotropic media*
Joseph Kremor A D and Khalid Amrouch B CA Woodside Energy Ltd., 240 St Georges Terrace, Perth, WA 6000, Australia.
B Australian School of Petroleum, University of Adelaide, North Terrace, SA 5005, Australia.
C Centre for Tectonics Resources and Exploration (TRaX), Department of Physical Sciences, University of Adelaide, Adelaide, SA 5005, Australia.
D Corresponding author. Email: joseph.kremor@woodside.com.au
The APPEA Journal 57(2) 772-775 https://doi.org/10.1071/AJ16244
Accepted: 28 March 2017 Published: 29 May 2017
Abstract
A methodology of calculating anisotropy parameters in horizontally transverse isotropic (HTI) media using a Backus average-like algorithm is presented herein. Anisotropy parameters in HTI media are calculated by mapping the stiffness parameters that exist in HTI media and vertically transverse isotropic (VTI) media by tilting the Christoffel equations. Fast and slow transverse waves, compressional wave and density logs are used as inputs into the averaging algorithm and, from these, anisotropy parameters are calculated over a predefined averaging window. From the results, the horizontal compressional wave velocity in the direction of the symmetry plane of isotropy can be determined, as can the compressional wave velocity that is perpendicular to the symmetry plane. When the anisotropy is caused by a single set of vertical fractures, these correspond to the directions perpendicular to and parallel to the fracture plane respectively. In cases where the thickness of the bed of interest is thin, a workflow is presented to choose an averaging length that will allow for the calculation of anisotropy parameters and velocities in thin beds. This technique was applied to a coal seam gas well situated in the Surat Basin and anisotropy parameters were calculated over two horizons.
Keywords: Backus average, coal seam gas, petrophysics, seismic.
Joseph Kremor has been a graduate data scientist at Woodside Energy 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. |
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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