Mohamed Careem Mohamed Nasvi
University of Peradeniya
Dr. Nasvi received his BSc (Eng) degree (First Class Honours and University prizes) from University of Peradeniya, Srilanka in 2009 and after that he worked as a temporary lecturer in the same university for a period of one year. He obtained his PhD degree in Geotechnical Engineering from Monash University, Australia in 2013. His PhD thesis title was “Geopolymer as well cement for geological sequestration of carbon dioxide”. At present, he is working as a senior lecturer at department of Civil Engineering, University of Peradeniya, Srilanka. He has published many journals and conferences in the areas of carbon capture storage, oil adn gas and energy fields.
Carbon capture and storage (CCS) is found as a viable method for long-term reduction of greenhouse gases. In a CCS project, mechanical integrity of well cement should be maintained to sustain the required mechanical strength throughout the life of an oil/gas and CO2 sequestration well. One of the major issues with existing OPC based oil well cement is cement degradation in CO2-rich environments. On the other hand, researchers have found that geopolymer cement possesses excellent acidresistant characteristics, shows higher mechanical strength and durability and demonstrates lower permeability. Therefore, this research work focused on studying the mechanical integrity of geopolymers under two different conditions: (1) effect of CO2 on mechanical behaviour of geopolymers and (2) hydraulic fracturing of geopolymers to study the mechanical integrity under down-hole stress conditions. To study the emchanical integrity under CO2 rich environment, fly ash-based geopolymers were tested in CO2 chamber at apressure of 3 MPa for up to 6 months and uniaxial compressive strength testing was conducted to study the mechanical behaviour of geopolymer in CO2. It was noted that there are no significance changes in compressive strength and Young’s modulus of geopolymer in CO2 after 6 months. The variations in compressive strength values in CO2 were within 2% compared to the compressive strength value prior to CO2 exposure. Scanning electron microscopy (SEM) testing was conducted to study any microstructural changes in CO2, and the SEM results revealed no significance variation in the microstructure of geopolymer after 6 months of CO2 exposure.For hydraulic fracturing experiment, four different tests were conducted by changing the injection pressure (Pin), axial stress (σ1), confining pressure (σ3) and tube length (30 mm and 40 mm). Geopolymers could not be fractured in any of the tests, which employed maximum values of Pin and σ1 as 23 MPa and 59 MPa respectively. Even though maximum ratios of Pin/ σ3 of 3.8 and σ1/ σ3 13.3 were used, fracture development was not observed. The results of this experiment lead to the conclusion that geopolymers can provide the required mechanical integrity in CO2 injection wells, as the absence of fractures in geopolymer under extreme stress conditions eliminates one of the possible CO2 leakage pathways.