Modeling of CO2 Leakage up Through an Abandoned Well from Deep Saline Aquifer to Shallow Fresh Groundwaters

Abstract

This article presents a numerical modeling application using the code TOUGHREACT of a leakage scenario occurring during a CO 2 geological storage performed in the Jurassic Dogger formation in the Paris Basin. This geological formation has been intensively used for geothermal purposes and is now under consideration as a site for the French national program of reducing greenhouse gas emissions and CO 2 geological storage. Albian sandstone, situated above the Dogger limestone is a major strategic potable water aquifer; the impacts of leaking CO 2 due to potential integrity failure have therefore to be investigated. The present case study illustrates both the capacity and the limitations of numerical tools to address such a critical issue.The physical and chemical processes simulated in this study have been restricted to:(i) supercritical CO 2 injection and storage within the Dogger reservoir aquifer, (ii) CO 2 upwards migration through the leakage zone represented as a 1D vertical porous medium to simulate the cement-rock formation interface in the abandoned well (iii) impacts on the Albian aquifer water quality in terms of chemical composition and the mineral phases representative of the porous rock by estimating fluid-rock interactions in both aquifers. 2Because of CPU time and memory constraints, approximation and simplification regarding the geometry of the geological structure, the mineralogical assemblages and the injection period (up to 5 years) have been applied to the system, resulting in limited analysis of the estimated impacts.The CO 2 migration rate and the quantity of CO 2 arriving as free gas and dissolving, firstly in the storage water and secondly in the water of the overlying aquifer, are calculated. CO 2 dissolution into the Dogger aquifer induces a pH drop from about 7.3 to 4.9 limited by calcite dissolution buffering. Glauconite present in the Albian aquifer also dissolves, causing an increase of the silicon and aluminium in solution and triggering the precipitation of kaolinite and quartz around the intrusion point. A sensitivity analysis of the leakage rate according to the location of the leaky well and the variability of the petro-physical properties of the reservoir, the leaky well zone and the Albian aquifers is also provided.

Developments since 2005 in understanding potential environmental impacts of CO2 leakage from geological storage

“…Geochemical modelling has been applied thus far to assess monitoring options (Carroll et al, 2009), for the interpretation of observed changes at natural analogue sites (Keating et al, 2010;Keating et al, 2013a;Lions et al, 2014b;Viswanathan et al, 2013), for the prediction of potential impact on groundwater chemistry (Carroll et al, 2014;Humez et al, 2011;Navarre-Sitchler et al, 2013;Wilkin and DiGiulio, 2010), the fate of trace metals in shallow groundwater (Wang and Jaffe 2004;Birkholzer et al 2008;Zheng et al 2009 and2013;Siirila et al, 2012), and to better understand the significance of microbially mediated reactions . It is also being used to interpret observed groundwater changes at CO 2 injection field experiments Yang et al, 2013a;Yang et al, 2014b;Zheng et al, 2012).…”

“…XRD, SEM-EDS) (Keating et al, 2010;Keating et al, 2013b;Viswanathan et al, 2013;Zheng et al, 2012;Zheng et al, 2009). Such complex mineralogy allows one to predict impacts on water composition and the precipitation / dissolution of the main minerals (Humez et al, 2011;Zheng et al, 2012;Zheng et al, 2009). In this case, incorporation of kinetic rates helps to describe the evolution of the system.…”

pH, geoelectrical and membrane flux parameters for the monitoring of water-saturated silicate and carbonate porous media contaminated by CO2

“…However, the goal of the sequestration may be compromised by leakage of stored CO 2 which can take place due to high permeability pathways around the existing well bore [4], nearby leaky wells [5], [6], fractures around caprocks [7], wettability alteration of the caprocks [8], and so on. In certain circumstances, it is feared that the vertical or upward migration of the leaked CO 2 from the sequestrated aquifer may encounter overlying aquifers with potable water resulting in contamination of the water [5], [9], [10].…”

“…From a flow system point of view, the CO 2 contamination of the potable water aquifers can be visualised as two-phase static system with the water in porous media remaining static while the contaminating plume of CO 2 imposed a pressure head at the boundary [5], [17].…”

Simulating the Flow of Variable-salinity Water in Response to CO2 Injection

“…While previous studies have investigated the impacts of CO 2 injection on water flow and brine displacement [2,3,4,5,6,7], only a few have specifically accounted for the flow of variable-salinity formation water [8,9]. This paper presents results from various 2D and 3D numerical simulation studies with Eclipse and TOUGH2 that model the degree of salinity changes in response to CO 2 injection.…”