Coupled fluid flow and elasto-plastic damage analysis for fractured porous chalk with induced wormhole

• We developed an integrated model, which couples the flow in porous media with nonlinear fractured material.
• The geomechanic model includes the intact chalk, natural fractures and the induced wormhole. An equivalent coupled elasto-plastic damage constitutive, with continuum approach, is developed to analyze the linear and nonlinear behavior of the chalk and natural fractures.
• We examined the effects of the natural fractures orientation in respect to the wormhole on the chalk and the wormhole's strength and deformation.
• Increasing the flow discharge from the outlet boundary, leads to the damage, asperity degradation and failure around the wormhole walls.
• The asperity degradation increases the fracture aperture, which results the chalk permeability enhancement; however, results show the asperity degradation has an insignificant effect on the flow flux from the outlet boundary.

Acid injection in a carbonate oil reservoir can increase oil recovery by etching a part of the fractured porous reservoir and generating conductive channels (“wormholes”), which creates an easier path for oil production. However, it is crucial to predict the wormhole and reservoir strength and their failure for a successful acid treatment. For this purpose, a continuum-based computational method is developed. The model includes flow in the porous chalk reservoir, flow in the wormhole and reversible and irreversible deformation of chalk and fractures, which are modeled with an equivalent elasto-plastic damage constitutive model. The coupling between the reservoir flow and the fractured chalk deformation is done by explicit coupling method. The results found that the risk of the wormhole's walls failure is higher if the natural fractures are oriented along the wormhole; however, natural fractures with larger dip angles and higher inclinations in respect to the wormhole increase the risk of the rock failure. Results shows that increased fluid production from the wormhole, which can be the result of the further acid treatments, developing irreversible behaviors of the rock and reduces the natural fracture asperity at the wormhole's tip, in addition to increasing the wormhole's wall deformation, eventually leading to the wormhole's occlusion.