Oil wells are engineering structures that should last safe and sound for decades. Its integrity should be guaranteed not only during drilling but also throughout the life of the reservoir. Reservoir production generates stress changes within the reservoir as well as throughout the surrounding rocks. These stress changes cause displacements and strains around existing wells that may lead to undesired casing deformation and eventually to its failure. The aim of this paper is to describe the geomechanical workflow to deal with wellbore integrity during the life of the reservoir. The stress and displacement fields developed during reservoir production are evaluated through the use of a coupled stress-flow analysis. Since the stresses are defined within large volumes of rocks, a special workflow has to be followed in order to define the stress field at the scale of the wellbore. It is presented an application example of a real reservoir considering a blackoil model containing producer and injector wells. It was made a submodel analysis around the producer well, considering the results of two global models simulated using one and two-way partial coupling. The results showed the workflow applicability and the importance of employing a rigorous fluid mechanical methodology in well integrity analysis.
Current challenges in the extraction of hydrocarbons include the exploration of deep reservoirs, which are often part of highly complex geological scenarios, as well as the drilling and completion of wells, in broad spectrum of directions, in such formations. From the geomechanical point of view, the problematic of wells and reservoirs is often distinctly addressed, mainly because of the scale difference between such entities. Although the system behaves in an integrated way, the association of the phenomena involved in the analysis of wells and reservoirs is frequently neglected. The wells are linear constructions whose geomechanical behavior is closely related to the stress state of the rock which is going through, to the fluid employed during drilling, to the drilling direction and to the casing type. By the activities performed through the well, the reservoir undergoes significant changes in its equilibrium configuration, once the production (or injection) of fluid in the porous medium causes significant variations in their pore pressure and therefore in its stress state. Nevertheless, the reactions of the reservoir to the effects of development are not concentrated only within its borders, but they spread through the adjacent rocks, many of which are crossed by wells that propel the geomechanical changes. Clearly, there is what may be called well-reservoir system, since the behaviors of entities involved are not independent of each other, mainly due to the aforementioned stress state morphology.
