Estimating hydraulic parameters of the Açu-Brazil aquifer using the computer analysis of micrographs

•We obtain hydraulic parameters by processing the images of thin rock sections.•We segment the samples and geometrically characterize the Representative Elemental Volume to compute the porosity.•Permeability is estimated by performing flow analysis in the reconstructed 3D model.

SummaryThe conventional way of obtaining hydraulic parameters of aquifers is through the interpretation of aquifer tests that requires a fairly complex logistics in terms of equipment and personnel. On the other way, the processing and analysis of digital images of two-dimensional rock sample micrographs presents itself as a promising (simpler and cheaper) alternative procedure for obtaining estimates for hydraulics parameters. This methodology involves the sampling of rocks, followed by the making and imaging of thin rock samples, image segmentation, three-dimensional reconstruction and flow simulation. This methodology was applied to the outcropping portion of the Açu aquifer in the northeast of Brazil, and the computational analyses of the thin rock sections of the acquired samples produced effective porosities between 11.2% and 18.5%, and permeabilities between 52.4 mD and 1140.7 mD. Considering that the aquifer is unconfined, these effective porosity values can be used effectively as storage coefficients. The hydraulic conductivities produced by adopting different water dynamic viscosities at the temperature of 28 °C in the conversion of the permeabilities result in values in the range of [6.03×10-7,1.43×10-5] m/s, compatible with the local hydrogeology.