Simulation of the degradation of oilwell cement for the prediction of long-term performance

The cement sheath surrounding a wellbore forms an important barrier to maintain well integrity beyond the service life of a well. The understanding of the potential degradation of well cement, as a result of exposure to groundwater, is therefore necessary to determine if this barrier remains intact or remedial action is required at some time in the future. A reactive transport model of a well cement is developed and calibrated to accelerated laboratory tests. The calibrated model of cement is subsequently exposed to different groundwater compositions for a simulated time period of 1000 years. The results of these simulations demonstrate that the groundwater composition affects the long term degradation through the dissolution of portlandite and C-S-H. The precipitation of calcite has a protective effect by filling the pore space and subsequently reducing the intrusion of aggressive aqueous species in the surrounding formation. (C) 2019 Elsevier Ltd. All rights reserved.