Facies and petrophysical modelling of a thick lower cretaceous tsunami deposit in E Spain: Up-scaling from sample to outcrop scales

Abstract

The tsunami deposit (up to 3 m thick) of the Cretaceous Camarillas Formation in the Galve sub-basin (eastern Spain) is characterized by a large lateral extent (35 km(2)) and facies uniformity, consisting in fine to coarse subarkosic-arkosic sandstones. At the scale of outcrop observation, different lithofacies were distinguished and related to sedimentation processes. Sand facies distribution conditioned the fades heterogeneity at both mesoscopic or outcrop scales (10(-1)-10(1) m scale) and sample scale (10(-3)-10(-2) m). The sample features were up-scaled to that of a facies model using probability functions and variograms as well as to outcrop-scale data (geometry and size) of facies distribution, and it showed a good correlation with the facies distribution at the outcrop. Porosity is strongly correlated to permeability and the pairs of porosity and permeability values fall into the global hydraulic element (GHEs) 5, so that they can be up-scaled into reservoir models in terms of hydraulic properties. From data analysis, no apparent link between sand sorting and porosity and permeability values was observed. The petrophysical models, which were independent of facies models, were up-scaled taking into account the porosity and permeability values from sample data and the statistical analysis of their distribution along the outcrop. The permeability model was carried out as a function of porosity by applying a linear relation, which simplified the modelling process and discarded permeability uncertainties linked to fades distribution in the deposit In spite of different source data, the petrophysical models show a distribution of lower and higher values that resembles the facies model. Consequently, our modelling results clearly suggest the link of facies type and their grain size distributions with the petrophysical properties into the deposit. Consistency between fades and petrophysical models and outcrop-scale observations make it possible to extrapolate to other deposits related to similar sedimentary processes.