High-fidelity field-scale simulation of CO2 dissolution into brine for a fully saturated porous media to capture heterogeneity and thermodynamic response functions on convective dynamics

Carbon dioxide (CO₂) dissolution into brine at deep reservoir conditions is a complex non-linear process that introduces significant challenges for large scale characterization. A comprehensive understanding requires exploring the entire physical parameter space that governs the system dynamics and modelling this behavior with much needed realism. In brief, the dissolution of CO₂ into brine creates a density stratification by forming a high-density diffusive layer on top of low-density brine and creates a Rayleigh-Taylor type instability.  This instability results in the diffusive front disintegration and gives rise to dense downwelling fingers that facilitate dissolution.  Over the past few decades, research has investigated fingering dynamics for homogeneous and heterogeneous cases, under the influence of background flow. However, a full-scale study collectively considering the interplay of all the different parameters remains to be done.  Our objective lies in bridging this knowledge gap to understanding the overall system comprehensively.

 

We use our recently developed particle-based reservoir simulator, PyDDC, to model the entire transport phenomenon subject to a wide range of reservoir input parameters. We model the heterogeneity using multi-Gaussian random fields and use our thermodynamic module, co2br, to compute the intensive parameters. We will first show the system response to heterogeneity in a Peclet-dominated regime and then introduce variations in pressure, temperature and electrolyte compositions to generate a wide range of Rayleigh numbers to model the entire behavior in a mixed regime.  We will investigate how individual physical parameters define the finger morphology and plume deformation in the mixed regime and perform sensitivity analysis to comprehensively understand which factors have the predominant influence. We will also highlight the salting out effect for a wide range of multi-component electrolytes and investigate their influence on regime transitions. We have uncovered trends of CO₂ dissolution rate as a function of anionic species in brine and found a dependence of convective onset time and critical finger wavelength on different electrolyte compositions. We identified clusters based on which the electrolytes can be grouped that show similar and antithetic influences on dissolution and mixing. We found temperature and salinity dependence of Sherwood number and global scalar dissipation rate which will help us understand the global mixing behavior. Finally, we will also look at how perturbations develop based on the system response to those physical variables and understand qualitatively how they govern the entire dynamics.