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Journal of the Australian Society of Exploration Geophysicists
RESEARCH ARTICLE

Assessing the repeatability of reflection seismic data in the presence of complex near-surface conditions CO2CRC Otway Project, Victoria, Australia

Yousuf Al-Jabri 1 2 3 Milovan Urosevic 2 3
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1 Petrulum Development Oman, Oman, Curtin University of Technology and CO2CRC, Perth, WA 6845, Australia.

2 Department of Exploration Geophysics, Curtin University of Technology, GPO Box: U1987 Perth, WA 6845, Australia.

3 Corresponding authors. Email: Yousuf.Aljabri@postgrad.curtin.edu.au; M.Urosevic@curtin.edu.au

Exploration Geophysics 41(1) 24-30 https://doi.org/10.1071/EG09010
Submitted: 11 February 2009  Accepted: 14 December 2009   Published: 19 February 2010

Abstract

This study utilises repeated numerical tests to understand the effects of variable near-surface conditions on time-lapse seismic surveys. The numerical tests were aimed at reproducing the significant scattering observed in field experiments conducted at the Naylor site in the Otway Basin for the purpose of CO2 sequestration. In particular, the variation of elastic properties of both the top soil and the deeper rugose clay/limestone interface as a function of varying water saturation were investigated. Such tests simulate the measurements conducted in dry and wet seasons and to evaluate the contribution of these seasonal variations to seismic measurements in terms of non-repeatability. Full elastic pre-stack modelling experiments were carried out to quantify these effects and evaluate their individual contributions. The results show that the relatively simple scattering effects of the corrugated near-surface clay/limestone interface can have a profound effect on time-lapse surveys. The experiments also show that the changes in top soil saturation could potentially affect seismic signature even more than the corrugated deeper surface.

Overall agreement between numerically predicted and in situ measured normalised root-mean-square (NRMS) differences between repeated (time-lapse) 2D seismic surveys warrant further investigation. Future field studies will include in situ measurements of the elastic properties of the weathered zone through the use of ‘micro Vertical Seismic Profiling (VSP)’ arrays and very dense refraction surveys. The results of this work may impact on other areas not associated with CO2 sequestration, such as imaging oil production over areas where producing fields suffer from a karstic topography, such as in the Middle East and Australia.

Key words: time-lapse/near-surface conditions.


Acknowledgment

The authors would like to thank CO2CRC, for the full access to Otway Basin Pilot Project (OBPP) database. In particular we acknowledge help provided by Dr A. Kepic and Dr D. Sherlock with field data design and acquisition. Petroleum Development Oman (PDO) is acknowledged for providing Yousuf with a PhD scholarship. We are grateful to Tesseral Technologies Inc., Hampson & Russell Software Services and Landmark Graphics for providing software packages and support.


References

Al-Jabri Y. , and Urosevic M. , 2008, The applicability of vibroseis sources for the land seismic time-lapse surveys; CO2 sequestration field: CO2CRC Otway Project, Victoria, Australia: Vibroseis Workshop 2008, Prague, Czech Republic, 13–15 October 2008.

Al-Jabri Y. , Urosevic M. , Evans B. , and Sherlock D. , 2008 a, Understanding seismic repeatability in the presence of irregular near-surface conditions (karst): CO2CRC Otway Project, Victoria, Australia: SEG & EAGE Summer Research Workshop 2008, Vancouver, Canada, 7–12 September 2008.

Al-Jabri Y. , Urosevic M. , and Kepic A. , 2008 b, The effects of the near-surface weathered zone on the CO2 time-lapse monitoring program at Naylor-1, CO2CRC Otway Project, Victoria, Australia: CO2CRC Symposium 2008: Queenstown, New Zealand, 1–5 December 2008.

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Urosevic M. , Sherlock D. , Kepic A. , and Dodds K. , 2007, “Land seismic acquisition repeatability for time-lapse monitoring of CO2 sequestration”: 19th International Conference of Australian Society of Exploration Geophysics, Perth, WA.

Urosevic M. , Sherlock D. , Kepic A. , Nakanishi S. , and Tcherkashnev S. K., 2008, “Time lapse VSP program for Otway basin CO2 sequestration pilot project”: 70th EAGE Conference & Exhibition – Rome, Italy.

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