Geomechanical Integrity of Fractured Reservoirs: Hydro-Mechanical Coupling

There is no more challenging task for today oil and gas production companies than simulating the production behavior of naturally fractured reservoir fields. These reservoirs are highly prosperous at their early stage of production, only to decline afterward. Previous behavior has risen awareness of the geomechanics role in controlling deliverability of those reservoirs. This is not a straight forward rock mechanics problem to tackle as it requires dealing with two different constituting continuums, matrix and fractures; that respond differently to solicitations. Hasdrubal is a naturally fractured reservoir field located in offshore Tunisia. Recently, the field has manifested serious integrity and water coning issues. An integrity study was necessary to accurately determine the ever-changing stress settings and assimilate their impact on the production trend. Thus, former geomechanical investigations of the field were revisited to acquire a strong understanding of the reservoir and so develop an appropriate Three- Dimensional Geomechanical Model (3D-GM) that incorporates the invasive impacts of faults/fractures on the mechanical and hydraulic behaviour of the field. The 3D-GM was initially deployed to appraise the alteration of the governing stresses and strains setting induced from the reservoir depletion before generating a reactivation potential map of the faults at current and future conditions, which showed again the reactivation of most of faults intercepted by the well notably the ones responsible of water production. A justification that the former investigation studies were not in position to offer it as they were grounded only on the 1D modelling approaches (i.e. intact model). Previous observation was confirmed through the built of a two dimensional finite model for the problematic well A1ST thus allowing us to compute displacement of the fault’s walls and accordingly interpret the new values of permeability associated to the different faults of the field. The up-to-date permeabilities were introduced to the dynamic reservoir model hence to estimate production trend of the A1ST1 well. A fair matching with field production data was achieved, proving again the reliability of the integral approach developed in this study in modelling the Hasdrubal field with high accuracy.