Abstract
Inhibiting natural gas hydrate (NGH) decomposition is a crucial challenge in NGH strata cementation. Lecithin can inhibit the decomposition of NGH, however, before lecithin is added to oil well cement to create a cement slurry system that inhibits NGH decomposition, the effects of lecithin on the mechanical properties of oil well cement must be considered. Therefore, in this research, the effects of lecithin on the mechanical properties of oil well cement were studied. The elastic modulus and compressive strength were measured to evaluate the mechanical properties. The changes in the mechanical properties of cement with different lecithin concentrations were experimentally studied. Through experimental research and inductively coupled plasma-atomic emission spectrometry (ICP-AES) analysis, it was confirmed that a 1.5% lecithin concentration in the cement slurry inhibits NGH decomposition. Quantitative calculations determined the ratio of lecithin to calcium silicate hydrate (CSH) gel in an atomic model when the lecithin concentration was 0, 0.5%, 0.8%, 1.0%, 1.2% and 1.5%, and the lecithin–CSH gel atomic model was established with different concentrations. According to molecular dynamics simulations and experimental analyses, the influence mechanism of lecithin on the mechanical properties of cement was revealed. The experimental and simulation results demonstrated that as the lecithin concentration increased, the elastic modulus and compressive strength of cement decreased, and the interfacial adsorption energy between lecithin and CSH gel increased. The decalcification of CSH gel by lecithin and the migration of calcium to the surface result in decreases in the elastic modulus and compressive strength of cement. The mechanical properties of cement can be enhanced by increasing the calcium content and reducing the number of calcium migration channels of calcium. Finally, we evaluated the impact of lecithin on the rheological properties and setting time of cement slurry. The research results are significant for the further development of cement slurry systems with NGH decomposition resistance.
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