A Sequential Splitting Strategy for CO2 Storage Modelling

Abstract

Research and development methodologies for the storage of CO2 in geological formation are in developing over the last 10 years. In this context, numerical simulators are the practical tools to understand the physical processes involved by acid gas injection and evaluate the long term stability of the storage. CO2 storage models can be seen as a mix between two types of models: a reservoir model coupling multiphase flow in porous media with local phase equilibria and an hydrogeochemical model coupling transport in aqueous phase with local chemical equilibria and kinetic reaction laws. In a recent paper, Nghiem et al. [1] proposed a fully-coupled method to solve this problem extending the local PVT-unknowns elimination strategy to geochemical problems. This paper presents a different approach which combine the two models in a single computation using a sequential splitting method. The main advantage of this approach is the ability to choose a specific numerical scheme for each model. From a mathematical point of view, this method can be seen as a two stage time integration scheme. At each stage we compute an approximate solution of the main problem using some predicted terms estimated from previous stages. This scheme is a sequential splitting strategy so it may induce some numerical errors relevant for the physical coherence of the model. To correct this error without using any iterative method, we propose to use a correction stage. This method has been implemented in a research computer code. The code is applied to model a field-scale CO2 storage in an heterogeneous saline aquifer. [1] Long Nghiem, Peter Sammon, Jim Grabenstetter and Hiroshi Ohkuma, ”Modeling CO2 Storage in Aquifers with a Fully-Coupled Geochemical EOS Compositional Simulator”, SPE 89474, April 004.