Large to intermediate-scale aquifer heterogeneity in fine-grain dominated alluvial fans (Cenozoic As Pontes Basin, northwestern Spain): insight based on three-dimensional geostatistical reconstruction

Abstract

Facies reconstructions are used in hydrogeology to improve the interpretation of aquifer permeability.. In the absence of sufficient data to define the heterogeneity due to geological processes, uncertainties in the distribution of aquifer hydrofacies and characteristics may appear. Geometric and geostatistical methods are used to understand and model aquifer hydrofacies distribution, providing models to improve comprehension and development of aquifers. However, these models require some input statistical parameters that can be difficult to infer from the study site. A 3D reconstruction of a kilometer scale fine-grain dominated Cenozoic alluvial fan derived from a large number of continuously cored, closely spaced, and regularly distributed wells is presented. The facies distributions were reconstructed using a genetic stratigraphic subdivision and a deterministic geostatistical algorithm. The reconstruction is slightly affected by variations in the geostatistical input parameters because of the high-density data set. Analysis of the reconstruction allowed identification in the proximal to medial alluvial fan zones of several laterally extensive sand bodies with relatively higher permeability; these sand bodies were quantified in terms of volume, mean thickness, maximum area, and maximum equivalent diameter. These quantifications provide trends and geological scenarios for input statistical parameters to model aquifer systems in similar alluvial fan depositional settings.

Dépendance à la profondeur et modèles exponentiels de perméabilité dans des cônes de déjection graveleux

“…In sand and gravel, however, the sedimentary or permeability correlation length in the vertical direction is within only a few meters or even decimeters (Hess et al 1992;Jussel et al 1994;Rubin 2003;Falivene et al 2007); thus, a number of measurements are required to distinguish the vertical trend of geological heterogeneity. As an alternative, indirect methods using empirical equations of grain size, porosity or other factors in samples, give K values that approximately agree with measurements taken at the same depth (e.g., Vukovic and Soro 1992;Cheong et al 2008;Song et al 2009;Vienken and Dietrich 2011).…”

Hierarchical Bayesian model averaging for hydrostratigraphic modeling: Uncertainty segregation and comparative evaluation

“…The mean sand‐clay cutoff 0.41 is in agreement with the calculated sand proportion 0.40 from the electrical logs, which implies that the sand‐clay cutoff can be interpreted as the probability of occurrence [ Chilès and Delfiner , ]. While previous studies [ Johnson and Dreiss , ; Falivene et al ., ] consider a sand‐clay cutoff of 0.5 as a reasonable assumption. The calibration results show that a fixed cutoff 0.5 will result in an underestimation of sand proportion in this case.…”

A short geostatistical study of the three-dimensional spatial structure of fumonisins in stored maize

“…This could be achieved applying geostatistics. Three-dimensional geostatistics has been successfully applied to reconstruct the large to intermediate heterogeneity of aquifers (Falivene et al, 2007), to reproduce the spatial variability of rock mass quality for geological excavations (Stavropoulou et al, 2007) and to map three-dimensional water-quality data to better protect the future health of the Chesapeake Bay and its tidal tributary system (Chehata et al, 2007).…”