Characterization and Assessment of Long-term Porosity of Various Cement Formulations Utilizing Nuclear Magnetic Resonance (NMR) Technology

Abstract

The global increase in hydrocarbon demand has pushed the oil and gas industry to explore new reservoirs that were previously untapped due to the technological limitations associated with high-pressure and high-temperature conditions. This demand has concurrently driven the development of advanced well-construction materials capable of withstanding extreme environments while addressing the industry's environmental challenges. The production of conventional cement significantly contributes to carbon emissions, with approximately one kilogram of CO2 released for each kilogram of cement produced, accounting for nearly 9% of global human-related emissions. This underlines the need for sustainable alternatives to reduce the carbon footprint of well cementing.Geopolymers emerge as a viable solution, offering lower carbon emissions, high compressive strength, and superior resistance to chemical degradation, thereby aligning with the industry's sustainability objectives. This thesis explores the long-term NMR porosity behavior and pore size distribution of traditional cement (class G and class H) and geopolymers in well cementing, focusing on the effects of various additives, such as fly ash, silica flour, microcellulose, and microblock, across different curing conditions. A comprehensive study was conducted using Nuclear Magnetic Resonance (NMR) technology to monitor NMR porosity evolution over extended curing periods: 146 days at room temperature and 35 days at 75°C. Results showed that at room temperature, the addition of fly ash led to substantial NMR porosity reduction demonstrating the most significant impact by enhancing the cement matrix's densification. The NMR analysis revealed a consistent shift toward smaller pores over time, indicative of ongoing hydration and pozzolanic reactions. High-temperature curing demonstrated accelerated hydration and rapid porosity stabilization within the first 24 hours for fly ash-modified and geopolymer samples, which maintained stable NMR porosity levels throughout the testing period. The findings also suggests that increased fly ash content contributes to greater thermal stability and pore structure refinement under elevated temperatures. The study also established that prolonged curing time significantly influences NMR porosity reduction for all formulations in this work. Overall, this research provides practical guidelines for optimizing cement formulations to enhance wellbore integrity across diverse environmental conditions, with an emphasis on sustainable and durable solutions for the oil and gas industry.