(10c) Self-Repairing Cement Composites for Subsurface Applications

Wellbore failure at the cement lining is one of the most common drivers of reservoir intervention during geothermal energy and unconventional oil/gas production. The main causes for cement fracturing are chemically corrosive (typically hypersaline, CO₂ and H₂S-rich) environments, mechanical stress, and high temperatures (up to 190 °C in unconventional oil reservoirs and up to 350 °C in Enhanced Geothermal Systems). As a result, expensive and time-intensive production shutdowns and repairs are required. Intervention costs average $1.5million per wellbore without taking into consideration the economical losses as a result of production stoppage, which can be several million dollars depending on the time frame of plant in non-production mode. To address these problems we developed a thermally stable polymer-cement composite with self-healing properties while maintaining the required rheological (during pumping) and mechanical properties of typical wellbore cement. Characterization of these cementitious materials comprised evaluation of rheological properties, including density and consistency measurements; mechanical properties, including compressive strength, Young modulus, and fracture toughness; thermal, chemical, and morphological properties, SEM/EDX, X-ray diffraction, FTIR, total organic carbon, and TG-MS. We demonstrated that these novel composite formulations present all the requirements of standard wellbore cement and introduce self-healing capabilities as shown by reducing by up to 82% the permeability of mechanically-induced fractures in the 0.3-0.5mm aperture range. These polymer-cement composite materials could then represent a definite solution to wellbore failure, production stoppage and reservoir intervention during geothermal and fossil energy production. In this presentation we will briefly describe the concept and present experimental as well as modeling results obtained this far on this latest technology.