One of the aspects that impacts wellbore's performance is the ductile behavior that a reservoir-rock can experience when subjected to high evolving compressive effective stresses resulting from depletion. During production, the reservoir-stress path can move within the elastic domain while at the same time, the Near Wellbore (NWB) stress path moves inside the plastic region. Poroelastoplastic deformations induce NWB damages leading to high skin evolution, lowering production, and in some cases forcing well shutins. This paper shows that cumulative stress-strain responses at the reservoir scale level need to be carried onto the near wellbore region to assess properly any productivity or injectivity loss. The goal is to understand better factors affecting NWB performance and provide geomechanical analysis tools to assist interpretation of skin evolution. The analysis shows that reservoir stress paths do not always follow the NWB stress paths. Hence, the NWB region cannot detach its performance from the field scale's response. Results indicate that skin evolution remains associated with pressure fluctuations via permeability changes and, most notably to Volumetric Strain Changes (VSC). This finding allows utilization of volumetric strains as a tracking tool of skin evolution similar to skin monitoring from PTAs. Therefore, it is possible to track skin evolution as an evolution of volumetric strain. Furthermore, VSCs can point out the length and preferential orientations of geomechanical formation damage. As a result, better-inform decisions can be made, for instance, on stimulation type selection, hydraulic fracture impairment, and drawdown pressure limits as part of the wellbore productivity enhancement processes.
It is essential to understand the geomechanical impact of pressure changes in the near-wellbore region; such fluctuations alter the stress state and ultimately the reservoir rock's reaction. Ductile materials exhibit more pronounced effects than brittle rocks, particularly when in situ conditions are such that the wellbore is close to the rock yielding envelopes (Schutjens, P., 2001; Schultz, R., 2005). During production, the reservoir stress path can move within the elastic domain. Simultaneously, the Near Wellbore (NWB) stress path can move inside the plastic region, manifesting as an evolution of wellbore skin. Field observations indicate that NWB damage induced by rock deformations promotes high skin evolution over time, lowering production, and in many cases forcing well shut-ins (Ugoala, O., 2013). The industry faces the need for more applied geomechanics in coupling both reservoir and near wellbore region responses to better understand different field operational issues. For instance, tracking of mechanical skin evolution, estimation of flowing bottom hole pressure limits, completion damage, and induced deformation bands, among others, require geomechanical coupling between the reservoir and the altered zone around wellbores. Based on field observations, this paper illustrates that the stress-strain response at the reservoir-scale level needs to be carried onto the near-wellbore region to assess adequately any productivity loss. After evaluating and discarding all potential causes of skin development, the cases presented here deal with stress-induced wellbore damage related to production as the only root cause of skin evolution.
