@inproceedings{01HQN9309V1NQM0FQ21FSVNNGQ,
  abstract     = {{The lithological and stratigraphical heterogeneity of coastal aquifers has a great influence on saltwater intrusion (SI). This makes it difficult to predict SI pathways and their persistence in time and to quantify salinities based on petrophysics. In this context, electrical resistivity tomography (ERT) and induced polarization (IP) methods are receiving increased attention regarding the discrimination between saltwater-bearing and clayey sediments. To simplify the interpretation of ERT data, it is commonly assumed that the bulk conductivity mostly depends on the conductivity of pore fluid, while surface conductivity is generally disregarded in the spatial and temporal variability of the aquifers, particularly, once the aquifer is affected by the presence of saltwater. However, this can lead to misinterpretation for aquifers constituted by clay-bearing sand layers or alternating sand and clay layers. In this study, we rely on co-located data from drilled boreholes coinciding with the geophysical measurements to formulate petrophysical relationships between bulk and fluid conductivity in both presence and absence of clay content in the porous sediments. We investigate both the laboratory scale through spectral induced polarization (SIP, Figure 1) and field scale through the comparison of ERT and time-domain IP with electromagnetic logging and lithologs. First, the sedimentary samples from the drilled wells were classified according to their grained size distribution, and then analyzed in the lab using a SIP system using the four-point measurement method in controlled salinity conditions. Second, logging results were compared with the field data extracted from inversion imaging. We found that the formation factors of the different unconsolidated sedimentary classification are varying from 2.1 to 5.3 for coarse-grained sand and clay-bearing mixtures, respectively. The clay bearing sediments were revealed to be distributed in small lenses and discontinuously distributed along the Luy River Catchment. In addition, they are occasionally locally present around the saline part of the aquifers. In these circumstances, ERT/IP inversions do not have the resolution to unequivocally discriminate clay-rich zones from saline zones. The comparison with logging data shows that ERT and to a lesser extent IP are able to image the main trend observed in wells, but that sharp transition and thin layer are missed. The latter seems to have a huge influence on the salinity distribution, making ERT and IP data inappropriate to characterize small-scale variations. The assumption of homogenous geological media is therefore leading to overestimated SI in heterogeneous clay-bearing aquifers.}},
  author       = {{Cong Thi, Diep and Pham Dieu, Linh and Caterina, David and De Pauw, Xavier and Thi Huyen, Dang and Ho, Huu Hieu and Hermans, Thomas and Nguyen, Frédéric}},
  booktitle    = {{6th International Meeting on Induced Polarization (WIP2022), Abstracts}},
  keywords     = {{aquifer,saltwater intrusion,conductivity,resistivity,induced polarization}},
  language     = {{eng}},
  location     = {{Annecy, France}},
  pages        = {{36--37}},
  title        = {{Determining lab and field petrophysical relationship of unconsolidated sediments in the Luy River coastal aquifer though SIP and co-located geophysical well logs}},
  year         = {{2022}},
}