Dynamic Fluid Flow and Geomechanical Coupling to Assess the CO₂Storage Integrity in Faulted Structures

Abstract

-The SiteChar research on the Southern Adriatic Sea site focused on the investigation of the geomechanical and hydrodynamic behaviour of the storage complex in the case of CO 2 injection in a reservoir consisting of fractured carbonate formations. Special attention was paid to the effects that natural faults and fractures might have on CO 2 migration, and the effects that injection might have on the stability of faults. This assessment was originally performed via a hydro-geomechanical oneway coupling which relies on an adequate representation of faults in the model, allowing one to simulate fluid flow along the fault plane and inside faults as well as evolution of the stress state due to CO 2 injection. The geological model was populated with petrophysical and geomechanical parameters derived either from laboratory measurements performed on samples from a reservoir analogue, or published literature. Since only sparse data were available, various scenarios were simulated to take into account the uncertainties in the fluid flow and geomechanical properties of the model: the different state of faults ( i.e., open or closed) and various in situ stress state, commonly named geostatic stresses as the earth's crust deformation is assumed to be slow regarding the shortterm study. Various fluid flow parameters were also considered, although only one set of petrophysical data corresponding to the most realistic ones is considered here. Faults modeled as volumetric elements behave as flow pathways for fluids when they are conductive. The injected CO 2 migrates inside and through the Rovesti fault, which is located near the injection well. The fluid flow also induces overpressure in the faults. The overpressure in the Rovesti fault reaches 2.2 MPa while it reaches 4.4 MPa at the bottom hole of the injector. Extending to about 30 km, the pore pressure field reaches the Gondola fault located at 15 km from the injection zone but the overpressure does not exceed 0.1 MPa at such a distance from the injection well. Using this overpressure as loading in the geomechanical model allows one to compute the effective stress variation in the whole geological model. The total effective stress is then computed by adding an estimation of the regional stress. Post-processing is performed to derive the likely damage of the faults according to the MohrCoulomb criterion. The results are illustrated on the Rovesti fault, which is located near the injection well and consequently the most likely to be reactivated. On the basis of available data, for all the modeled scenarios (various initial stress regimes, closed or open fault), no fault damage is observed, as the stress state stays below the Mohr-Coulomb criteria.Résumé -Couplage des modélisations hydrodynamique et géomécanique pour évaluer l'intégrité d'un stockage de CO 2 dans des structures faillées -Les travaux de recherche conduits dans le projet SiteChar sur le site situé en mer Adriatique sud se sont concentrés sur le comportement géomécanique des formations carbonates fracturé...

Evaluation and Characterization of a Potential CO2Storage Site in the South Adriatic Offshore

“…Only the "NF" regime is discussed in this paper. The reader can refer to Baroni et al (2015) for results obtained with the SS135 stress regime.…”

“…This model is characterized by: -the petrophysical properties defined in Section 2.1.4, -a thermodynamic model based on an equation of state to simulate the different fluid states of the CO 2 at different temperatures and pressures, -a heat model, -an initial state, and -boundary conditions such as the injector. All these points are described in Baroni et al (2015). This model was applied on a refined mesh built from the geological gridding (Sect.…”

SiteChar – Methodology for a Fit-for-Purpose Assessment of CO2Storage Sites in Europe

“…These stresses are used to evaluate potential damage in the storage site strata and the overburden formations, in particular the likely generation of new fractures in the matrix or the likely propagation of existing fractures or faults, as illustrated in Baroni et al (2015). The models also predict expansion deformation of the storage sandstone due to CO 2 injection (Fig.…”

Evaluating the Sealing Effectiveness of a Caprock-Fault System for CO2-EOR Storage: A Case Study of the Shengli Oilfield

“…Although research on the structural control of fluid flow in hydrocarbon reservoirs is in nascent stages, various hydrocarbon leakage indicators have been identified for faults [22]. Integrity is a restraint on the fault sealing capacity, and it is currently a focal parameter in the literature; however, studies into the static sealing effectiveness of fault systems that consider CO 2 migration and the internal fault structure have made limited progress [23][24][25].…”