Multiphase Modeling of Geologic Carbon Sequestration in Saline Aquifers

Abstract

Geologic carbon sequestration (GCS) is being considered as a climate change mitigation option in many future energy scenarios. Mathematical modeling is routinely used to predict subsurface CO2 and resident brine migration for the design of injection operations, to demonstrate the permanence of CO2 storage, and to show that other subsurface resources will not be degraded. Many processes impact the migration of CO2 and brine, including multiphase flow dynamics, geochemistry, and geomechanics, along with the spatial distribution of parameters such as porosity and permeability. In this article, we review a set of multiphase modeling approaches with different levels of conceptual complexity that have been used to model GCS. Model complexity ranges from coupled multiprocess models to simplified vertical equilibrium (VE) models and macroscopic invasion percolation models. The goal of this article is to give a framework of conceptual model complexity, and to show the types of modeling approaches that have been used to address specific GCS questions. Application of the modeling approaches is shown using five ongoing or proposed CO2 injection sites. For the selected sites, the majority of GCS models follow a simplified multiphase approach, especially for questions related to injection and local-scale heterogeneity. Coupled multiprocess models are only applied in one case where geomechanics have a strong impact on the flow. Owing to their computational efficiency, VE models tend to be applied at large scales. A macroscopic invasion percolation approach was used to predict the CO2 migration at one site to examine details of CO2 migration under the caprock.

3D Pressure‐limited approach to model and estimate CO2 injection and storage capacity: saline Mount Simon Formation

“…On the basis of the VE model, the horizontal movement of the injected CO 2 is assumed to be more extensive at both spatial and temporal scales than its vertical movements . In the VE model, the CO 2 movement is numerically modeled only on a two‐dimensional (2D) horizontal plane, and the results are projected into the perpendicular dimension by implementing the relevant analytical expressions that are obtained on the basis of an assumption that the flow system is in vertical equilibrium at a given time . Although the overall accuracy of the model's predictions is reduced, the VE model's simplification and associated modifications practically reduce the number of dimensions (and hence the required grids), accelerate the speed of simulation by an order of magnitude, and consume significantly less computer memory than conventional three‐dimensional (3D) simulators.…”

Robust simulation of sharp-interface models for fast estimation of CO2 trapping capacity in large-scale aquifer systems

“…Apart from the open-source implementation, the novelty of our work lies in a flexible and robust formulation that unifies work from the early period of reservoir simulation [15][16][17][18], when practical numerical aspects were primarily in focus, with recent extensions of the VE framework [19] that focus more on physical effects related to large-scale CO 2 injection. The validity of the simplifying assumptions underlying VE models has been studied both with respect to spatial [20] and temporal [21] scales, and the utility of VE models is thoroughly discussed in, e.g., [22,23]. Early studies focused on VE models with a sharpinterface assumption [24][25][26], and models that only account for the basic effects of buoyant migration were successfully used to simulate long-term migration in the Utsira [27] and Johansen [28] aquifers.…”

Two risk metrics for CO2storage reservoirs with varying domain size, heterogeneity, and injection rate

“…In this regard, the focus of past studies has been to understand the behavior of these systems, including migration within the storage reservoir, chemical reaction with geologic media, potential leakage through wells, leak through the caprock, potential leakage through faults and fractures, and impact of variable injection schemes . Some studies have also considered the impact of these phenomena as a function of scale and various multiphase modeling approaches for CO 2 storage . Many of these studies have been helpful in increasing our fundamental knowledge of the processes at small to regional scale.…”