D.7.2 Fluid flow modeling coupled with geomechanics, Southern Adriatic Site

Deliverable D.7.2 Fluid flow modeling coupled with geomechanics, Southern Adriatic Site

The D.7.2 report is dedicated to the investigation of the geomechanical and dynamic behaviour of the South Adriatic site studied in SiteChar (WP7). It includes experimental analysis of data sampling from an onshore analogue performed by AGH, investigation of the cap rock integrity performed by SINTEF and investigation of the geomechanical and dynamic behaviour of the Grazia reservoir performed by IFPEN.

An onshore carbonate succession showing facies of basin similar to those drilled offshore, in correspondence of the potential storage site, was identified and analogue samples collected on land in the area of Vieste-Peschici (Gargano promontory). The samples consisted of limestones (reservoir analogue) of the Turonian-Senonian Scaglia Formation and marls (caprock analogue) of the Lower Aptian Fucoids Marls Formation. The objective of AGH work was to deliver large data set necessary to integrate full reservoir and geomechanical models. To characterise the reservoir level of the offshore area South Adriatic site, AGH performed laboratory measurements of petrophysical properties on an onshore analogue’s cap rock/reservoir cores. The following properties were characterised: porosity, irreducible water saturation, threshold pressure, permeability. Selected mechanical properties were investigated.

The objective of SINTEF's work was to demonstrate the use of numerical modelling for prediction of man-induced fracturing during fluid injection in geological formations. The numerical method chosen for this study was the Modified Discrete-Element Method (MDEM) developed at SINTEF and implemented in an in-house computer code. The MDEM software is two-way coupled to a commercial reservoir simulator, TOUGH2, which enables a coupled simulation of deformation, fluid flow and fracture propagation in rock. A two-dimensional model of the formation around the Grazia well was prepared including several facies with different properties, and two nearby faults. Modifications were made to the MDEM code to include the effect of gravity. Simulations have revealed that it was difficult to obtain an initial equilibrium before injection because the material around faults underwent uncontrolled fracturing caused by stress concentration near faults. After removing the faults, the simulation ran correctly and produced a fracture network. This validates the concept of MDEM as a fracture modelling tool, but at the same time raises the issue of how to include faults in a fracture code. Further work is needed in order to be able to successfully predict fracture development in complex geological formations including large scale features (faults).

The objective of IFPEN's work was to validate a coupled fluid flow and geomechanical model to simulate the dynamic and geomechanical behaviour of a potential CO₂ storage site including and demonstrating the methodology to assess the geomechanical integrity of a fractured site. The geological model was built by OGS in SiteChar at basin scale. Fluid flow and geomechanical parameters required to fill the model cells come mainly from AGH measurements, or literature (e.g. for initial stress state). Various representations of faults according to the modelling purpose have then been integrated in the model to simulate fluid flow along the fault plan and stress evolution due to CO₂ injection. Various scenarios were simulated to take into account the uncertainties on the petrophysical and geomechanical properties of the model: different states of faults (i.e., open, closed or mid-opened), stress (i.e., normal faulting, or shear stress with various angles) as well as fluid flow parameters. The final post processing shows that the Rovesti fault which is located near the injection well remains below the chosen Mohr-Coulomb criteria.