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On the usage of diffractions in ground-penetrating radar reflection data; implications for time-lapse gas migration monitoring

Hemin Yuan, Majken C. Looms and Lars Nielsen
On the usage of diffractions in ground-penetrating radar reflection data; implications for time-lapse gas migration monitoring
Geophysics (July 2020) 85 (5): H83-H95

Abstract

Time-lapse ground-penetrating radar (GPR) measurements are used to image/monitor, for example, water infiltration, water table changes, and fluid/gas flow patterns. Although crosshole GPR is often preferred over surface-reflection GPR in such studies, its application is limited by the selected borehole geometry, which may be difficult to define in an optimal way, especially in experiments in which flow pathways are difficult to predict. Surface-reflection GPR data sets are generally faster to collect over relatively large areas and are therefore more efficient for covering the volume when a fast-moving tracer (e.g., gas) may infiltrate a heterogeneous subsurface medium. We have used a diffraction imaging approach on time-lapse surface-reflection GPR data to detect changes in radar wave velocity associated with gas (CO (sub 2) ) injected into a heterogeneous chalk succession. We initially test and evaluate the diffraction imaging approach on synthetic GPR data. Afterward, we apply the methodology to time-lapse GPR field data, and we evaluate the robustness of using information from diffractions in light of the obtained data quality. The synthetic tests indicate that diffractions provide essential information for delimiting the area affected by gas in the heterogeneous chalk section studied. Our field experiment shows that using the diffraction information alone allows for detection of gas-affected zones and, therefore, potential flow characteristics of gas movement. We infer that the CO (sub 2) flow patterns in our study most likely are determined by small-scale fractures rather than the porosity/permeability of the rock matrix. Moreover, the approach used may serve as an initial study for future more targeted experiments or for further detail-retrieving full-waveform inversion.


ISSN: 0016-8033
EISSN: 1942-2156
Coden: GPYSA7
Serial Title: Geophysics
Serial Volume: 85
Serial Issue: 5
Title: On the usage of diffractions in ground-penetrating radar reflection data; implications for time-lapse gas migration monitoring
Affiliation: University of Copenhagen, Department of Geosciences and Natural Resource Management, Copenhagen, Denmark
Pages: H83-H95
Published: 20200728
Text Language: English
Publisher: Society of Exploration Geophysicists, Tulsa, OK, United States
References: 45
Accession Number: 2020-060750
Categories: Applied geophysics
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus.
N54°58'00" - N56°07'60", E10°55'00" - E12°48'00"
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2020, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by Society of Exploration Geophysicists, Tulsa, OK, United States
Update Code: 202017
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