Experimental and numerical simulation of thermodynamic properties of water-salt-gas mixtures (CO2 + co-contaminant) under geological storage conditions
Résumé
In the context of the reduction of greenhouse gas emissions, capture processes of CO2 constitute the main problem to solve. Indeed this step has the most important cost of all the treatment chain: capture/transport/sequestration. As a function of the industrial sources (energy production, iron industry, concrete production, etc.) and capture process, the composition of the gaseous mixture should vary considerably in nature and concentration. The degree of purity of captured CO2 is thus a key factor for transportation, injection and sequestration. In addition to CO2 and water, more or less important quantities of other gases (O2, N2, SOx, NOx, H2, CO, Ar...) would be admixed in different proportions. These gases are taken into account in industrial processes of capture but they remain poorly studied for the development of geological storage technologies. Furthermore, co-injected gases could mix with pre-existing natural gases (CH4, gas condensates, H2S) in depleted hydrocarbon reservoirs. Gas mixing could induce mineral dissolution – precipitation reactions and/or modifications of pressure - temperature properties of the system. The impact of such co-injected and/or residual gases on the mineral assemblages from reservoir, cap-rock and well-bore completion has to be understood under geological storage conditions at high pressures, high temperatures, and high salinity. In this context, a project called "Gaz Annexes" supported by the french national agency for research (ANR) was conducted since 2006 with some of the major actors working on the CCS in France, i.e. Nancy University and ENSIC, BRGM, IFP, Ecole des Mines de Paris and Total. The goal of the project “Gaz Annexes” is to acquire new data to characterize phase equilibria of geological systems including co-injected gases such as SOx, NOx, N2, Ar in order to improve our understanding of the reactivity of such systems. Hence, new thermodynamic data relevant for CO2 injection-storage conditions were measured and fitted to extract the lacking Equation Of State (EOS) parameters. The project is divided in five phases: i) Qualitative and quantitative compilation of co-injected gases generated as a function of industrial and capture processes. The goal is to determine which are the reactive gases and which quantity could be injected, ii) Acquisition of new experimental data on water/gas/salt systems by performing lab experiments and in situ measurements. Data are collected using two main analytical methods: chromatography and Raman spectroscopy, iii) Thermodynamic characterization of equilibrium between the different fluid phases (gas mixtures and saline waters), iv) Integration of the relevant new data into hydro-geochemical codes in order to better predict the behaviour of CO2 and co-injected gases into saline aquifers or oil reservoirs, v) Validation and application of developed geochemical codes on experimental data obtained on rock/water/gas systems with laboratory experiments carried out under geological conditions of storage. The chemical behaviour of co-injected (i.e., SOx, NOx, ...) gases if of prime interest if considering that such gases could generate very high acidity of the native brines and could accelerate the water – rock interactions. This could lead to an important impact on the petrophysical properties (porosity, permeability, etc.) of the whole reservoir. The region close to well bore of CO2 injection could be also drastically affected causing possible difficulties for the injectivity process. The obtained results will be presented for discussion at the GHG10 congress.