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TitleDetection of near-surface hydrocarbon seeps using P- and S-wave reflections
AuthorDuchesne, M J D; Pugin, A J M P; Fabien-Ouellet, G F O; Sauvageau, M S
SourceInterpretation vol. 4, no. 3, 2016., https://doi.org/10.1190/int-2015-0175.1
Year2016
Alt SeriesEarth Sciences Sector, Contribution Series 20150352
PublisherSociety of Exploration Geophysicists
Documentserial
Lang.English
Mediapaper; on-line; digital
File formatpdf
ProvinceQuebec
NTS31I/07
AreaSt. Lawrence Lowlands; Pointe-du-Lac
Lat/Long WENS -73.0000 -72.5000 46.5000 46.2500
Subjectsfossil fuels; geophysics; p waves; s waves; seismic surveys, ground; seismic reflection surveys; hydrocarbon potential; hydrocarbon migration; oil seeps; hydrocarbons
Illustrationsgraphs; cross-sections; location maps; seismic reflection profiles; tables
ProgramShale Gas - groundwater, Environmental Geoscience
AbstractThe combined use of P- and S-wave seismic reflection data is appealing for providing insights into active petroleum systems because P-waves are sensitive to fluids and S-waves are not. The method presented herein relies on the simultaneous acquisition of P- and S-wave data using a vibratory source operated in the inline horizontal mode. The combined analysis of P- and S-wave reflections is tested on two potential hydrocarbon seeps located in a prospective area of the St. Lawrence Lowlands in Eastern Canada. For both sites, P-wave data indicate local changes in the reflection amplitude and slow velocities, whereas S-wave data present an anomalous amplitude at one site. Differences between P- and S-wave reflection morphology and amplitude and the abrupt decrease in P-velocity are indirect lines of evidence for hydrocarbon migration toward the surface through unconsolidated sediments. Surface-gas analysis made on samples taken at one potential seeping site reveals the occurrence of thermogenic gas that presumably vents from the underlying fractured Utica Shale forming the top of the bedrock. The 3C shear data suggest that fluid migration locally disturbs the elastic properties of the matrix. The comparative analysis of P- and S-wave data along with 3C recordings makes this method not only attractive for the remote detection of shallow hydrocarbons but also for the exploration of how fluid migration impacts unconsolidated geologic media.
Summary(Plain Language Summary, not published)
A method using compressional-wave (PW) and shear-wave (SW) seismic reflection data is developed to detect hydrocarbon seeps. The method relies on the PW¿s sensitivity and SW¿s non-sensitivity to fluids. The method is tested in a prospective area of the St. Lawrence Lowlands in Eastern Canada. Differences between P- and S-reflection characteristics are indirect lines of evidence for hydrocarbon migration towards the surface. Surface-gas analysis made on samples taken at one potential seeping site reveals the occurrence of thermogenic gas that presumably vents from the underlying fractured source rocks forming the top of the bedrock. This seismic method presented in this contribution can be used for shallow hydrocarbon prospection, to circumscribe hazardous areas for drilling, for baseline studies required to assess groundwater quality control and to quantify methane fluxes into the atmosphere.
GEOSCAN ID297432