Effective Constitutive Relations for Simulating CO2 Capillary Trapping in Heterogeneous Reservoirs with Fluvial Sedimentary Architecture

TL;DR

This paper develops effective constitutive relations for simulating CO2 capillary trapping in heterogeneous fluvial reservoirs, capturing small-scale heterogeneity effects at larger scales to improve simulation efficiency and accuracy.

Contribution

It introduces a method to incorporate small-scale heterogeneity effects into larger-scale reservoir models through effective saturation relationships, enhancing simulation of CO2 trapping.

Findings

Effective saturation relationships improve modeling accuracy.

Method reduces computational costs in reservoir simulations.

Captures small-scale heterogeneity effects at larger scales.

Abstract

Carbon dioxide (CO2) storage reservoirs commonly exhibit sedimentary architecture that reflects fluvial deposition. The heterogeneity in petrophysical properties arising from this architecture influences the dynamics of injected CO2. We previously used a geocellular modeling approach to represent this heterogeneity, including heterogeneity in constitutive saturation relationships. The dynamics of CO2 plumes in fluvial reservoirs was investigated during and after injection. It was shown that small-scale (centimeter to meter) features play a critical role in capillary trapping processes and have a primary effect on physical- and dissolution-trapping of CO2, and on the ultimate distribution of CO2 in the reservoir. Heterogeneity in saturation functions at that small scale enhances capillary trapping (snap off), creates capillary pinning, and increases the surface area of the plume. The understanding of these small-scale trapping processes from previous work is here used to develop effective saturation relationships that represent, at a larger scale, the integral effect of these processes. While it is generally not computationally feasible to represent the small-scale heterogeneity directly in a typical reservoir simulation, the effective saturation relationships for capillary pressure and relative permeability presented here, along with an effective intrinsic permeability, allow better representation of the total physical trapping at the scale of larger model grid cells, as typically used in reservoir simulations, and thus the approach diminishes limits on cell size and decreases simulation time in reservoir simulations.