Abstract
Different surface seismic surveys have been recorded on an experimental hydrogeological site that has been developed for several years near Poitiers (France). The paper shows how 3D seismic imaging can be used to describe the near-surface heterogeneous aquifer. The acquisition spread is designed to perform both 3D refraction and reflection seismic surveying. Refraction survey enables us to obtain a 3D image in depth of a low velocity superficial zone contrasting with the underlying water – bearing carbonates. Variogram analysis and geostatistical filtering allow to filter random and structured acquisition noise. Factorial kriging is used to filter the small scale structures (cubic structure with a range of 55 m and nugget) in order to make the large scale structures appear and to determine their orientation: a main orientation N90 and a secondary orientation N50. These two directions have been selected to implement two deviated wells C3 and C4. Reflection survey enables us to get a 3D seismic pseudo velocity block in depth. The vertical resolution is enhanced thanks to deconvolution after depth conversion. A Wiener filter, defined at a reference well C1 has been applied to the seismic traces to convert into velocity the amplitude sections. The results obtained are validated at four wells (MP6, MP5, M8, M9) in which acoustic data have been recorded. The 3D seismic pseudo velocity block shows the large heterogeneity of the aquifer reservoir in the horizontal and vertical planes, confirms the main structural orientations (N90 and N50) pointed out by refraction survey. At a given depth, the velocity distribution shows preferential connections between wells. As an example, well pumping tests and pressure interference confirm the hydrodynamic connection between wells M13 and M21 defined by a low velocity zone at 88 m depth.
Highlights
Many underground aquifers were developed as experimental sites during the past decade
We propose to show the benefit of combining both 3D refraction and reflection seismic surveying in order to extract structural information from data recorded in near surface acquisitions
The field equipment is reduced to a 48-active channels recorder, a template composed of 48 vertical geophones and small charges of dynamite (25 g per shot point) at each source point. 20 templates have been implemented
Summary
Many underground aquifers were developed as experimental sites during the past decade. It clearly shows infinite apparent velocity events which are associated with reflected waves. The nugget effect and the small scale spherical model (5 m in the cross line direction), which have no physical meaning and are due to acquisition artefacts, have to be filtered during the estimation process Each shot point (cross spread) has been processed independently to obtain a single fold depth section with a sampling interval of 2.5 m (half the distance between 2 adjacent geophones) in the in line direction. No response Diffusivity < 1x103 m2.s–1 1x103 < D < 1x104 m2.s–1 1x104 < D < 1x105 m2.s–1 1x105 < D
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
