Analysis of hydration process of smelter slag plugging fluid activated with alkalis

•The slurry is hardened through the reorganization of the group and the reduction of the distance.•The confining pressure of the well wall helps increase the strength of the solidified body.•The increase in pore shrinkage causes the increase of relaxation time of intergranular water. The improper treatment of smelter slag is a prominent issue regarding environmental protection. To resolve this issue, we explored the possible application of a slag plugging fluid in the field of oil and gas field development. Specifically, the thermal effect during the hydration process, the microstructure, the water function mechanism, and the mechanical characteristics of a hardened body of the slag plugging fluid were investigated using a combination of characterization equipment including a hydration heat calorimeter, nuclear magnetic resonance (NMR) spectrometer, scanning electron microscope, NMR crosslink density meter, and medium-sized NMR analysis and imaging system. The results of this study show that the degree of polymerization of Si increases during the hydration process, accompanied by the generation of a large amount of 6-coordinated Al. At the same time, the spacing between particles is reduced by the physical and chemical reactions in the hydration product formed through the hydration reaction of the slag. This behavior causes the slurry to cement and harden. During the hardening process of the slurry, the water binding force, the water form, and the pore structure are all affected and changed by the components in the slurry. These combined effects further cause the T2 spectrum curve of water to change during the hydration process. Finally, a hardened slurry can form a slug that effectively seals the leaking channel. The theoretical results obtained from this study can help guide the recycling utilization of slag in the area of oil and gas field development. Such a direction will provide an effective means of resolving the slag treatment issue.