Simulação numérica da acidificação de carbonatos utilizando malhas obtidas a partir de imagens de MICRO-CT

Abstract

Matrix acidizing is one of the well stimulation techniques that consists of pumping an acid solution at a pressure lower than the fracture pressure of the rock. In carbonate formations, as a result of the acid-calcite reaction, part of the rock is dissolved and high conductivity channels, called wormholes, are created. One of the major challenges associated with simulating this type of process is to incorporate the heterogeneities inherent in carbonate rocks into the numerical meshes. The main objective of this work is to simulate acidification in carbonate rock plugs using the initial porosity field obtained from a microCT image. Two-scale modeling was used, with the balance of the amount of movement carried out using the Navier-Stokes-Brinkman approach. The simulations were carried out in a code developed in openFOAM, varying the speed of the acid on the face and obtaining the PVbt (Pore Volume to Breakthrough) for each condition. Mesh convergence analyses and the impact of varying the inlet interstitial velocity were carried out. Simulation results were compared with initial porosity fields generated using the uniform, normal and lognormal distributions. The initial porosity and permeability distributions obtained were consistent with the microCT image. Variations in the number of cells had no significant impact on the PVbt. By varying the injection speed on the face, it was possible to obtain the uniform, conical, branched, dominant wormhole, dissolution on the face and compact dissolution patterns, obtaining the PVbt curve to determine the optimum point (lowest PVbt). For the model developed from the image, the lowest PVbt obtained was 0.262 with an input speed of 4 2,12 10 m/s −  . For the models with uniform, normal and lognormal porosity distributions, the lowest PVbt values obtained were 0.276, 0.261 and 0.309 at an input speed of 5 8,3 10 m/s −  . The results presented showed that the methodology used to obtain porosity fields from microCT images can be used to obtain results that are more representative in terms of accounting for rock heterogeneities.