Semi-analytical model of brine and CO2 leakage through an abandoned plugged well. Applications for determining an Area of Review and CO2 leakage rate.

Arnaud Réveillère (1) , Jeremy Rohmer (1) , Frédéric Wertz (1)

1 BRGM - Bureau de Recherches Géologiques et Minières (BRGM)

Many CO2 storage projects consider aquifers located in sedimentary basins were past oil & gas operations have left wells with sometimes undetermined plugging history. Despite a careful site selection, a remaining risk of leakage outside the storage reservoir cannot be excluded, and potential leakage pathways have to be reviewed. Existing semi-analytical models can estimate the leakage flow rate of brine, possibly followed by CO2, from the storage aquifer to an overlying one (cf. publications by Nordbotten and co-authors, 2004-2009). In addition, several authors have proposed a definition of the "Area of Review" of CO2 storage sites as the area where the pressure changes due to the injection can drive the reservoir brine up to a shallower aquifer. In the present study, we combine these two approaches by developing a semi-analytical model able to consider the dynamic brine flow from the storage reservoir to an overlying aquifer through a vertical conduit. That leak is composed of an open wellbore and a porous column, whose characteristics are representative of degraded cements of an abandoned well. During the leakage, the saline brine coming from the storage reservoir progressively fills in the leak and replaces the original fluid, which was less saline and therefore less dense. When the lighter CO2 breaks through, it replaces part of the wellbore fluid by a lighter supercritical or gaseous phase, which increases the leakage. Simplified models of 2 phases flow in the wellbore are used. The model computes the transient leakage rate of brine followed by CO2, the progressive filling of the leak and several pressures variations. In a first application, we use this model for estimating the Area of Review and prioritizing the regions where potential pathways have to be examined. In a second application, the model is used for estimating the brine, and then the CO2 leakage flow rate up to the surface. The Paris region is chosen as a test site.

Mots clés: CO2 geological storage; brine leakage; CO2 leakage; semi-analytical model; risk assesment; area of review; stockage géologique de CO2; fuite de saumure; fuite de CO2; modèle semi-analitique; analyse de risque; impact en pression

Domaines: Sciences de l'environnement

Arnaud Réveillère, Jeremy Rohmer, Frédéric Wertz. Semi-analytical model of brine and CO2 leakage through an abandoned plugged well. Applications for determining an Area of Review and CO2 leakage rate.. 11th Annual Conference on Carbon Capture Utilization and Sequestration 2012 : CCUS 2012, Apr 2012, Pittsburgh, United States. ⟨hal-00709355⟩