Numerical Simulation and Evaluation of Absolute Permeability in Carbonates Using 3D Digital Models
Thaís M. G. Silveira1; William G. A. L. Silva1; Fernanda O. Hoerlle1; Paulo Couto1; José L. D. Alves1
1 Federal University of Rio de Janeiro
doi:10.20906/CPS/CILAMCE2017-0559
Resumo
Heterogeneous carbonate rocks present several challenges regarding their geomorphological characterization, petrophysical parameters analysis and full understanding of the fluid flow dynamics in their porous systems. In this approach, this work presents a numerical simulation of fluid flow using a 3D FEM model of Pre-Salt analogue carbonates (coquinas) and stromatolites to compute and evaluate absolute permeability. A numerical simulation based method is developed to predict absolute permeability using Digital Rock Physics techniques and the 3D model of rock porous media, which were previously published and proposed in another work. The X-Ray microtomography images of nine coquinas carbonate formation outcrop cores, from Morro do Chaves Formation (Northeast Brazil), and one stromatolite sample, from Lagoa Salgada (Rio de Janeiro), are used in this work. These coquinas samples have been largely studied as analogues of Santos Basin Pre-Salt carbonates. The fluid flow numerical simulation is performed with a commercially available software based on the Finite Element Method. Some premises are assumed to help the assembly of a large system of equations directly linked to the porous geometry and to shrink the high computational cost of the simulation. A numerical simulation of fluid flow at pore scale using the 3D models of analog coquinas was proposed and experimental data were used to validate the predictions of absolute permeability. The results suggest that the higher the resolution of computed microtomography images, the higher the number of pore pixels, the better pore connectivity, the higher the 3D model complexity, the greater the system of equations and thus, the higher the computational cost required to solve the fluid flow simulation. The mesh refinement, i.e. the variation in the number of degrees of freedom (DOF), is related to the number of elements within the 3D model and it is a key process to more accurately resolve the numerical simulation. The number of DOF and the time required to solve the
Palavras-chave: Pre-Salt Carbonate; Digital Rock Physics; Coquina; Numerical Simulation; Permeability; Porosity