Hybrid Bentonite-Zeolitic Imidazolate Framework Additive as an H2S Scavenger and Strength Enhancer for Class G Oil-Well Cement.

Optimization of cement slurry composition during well cementing jobs is highly critical to preserve well integrity under sour gas environments. This research focuses on the application potential of a hybrid bentonite-zeolitic imidazolate framework-67 (abbreviated as Bent/ZIF-67) as a hydrogen sulfide (H2S) scavenger for wellbore cementing. The performance of this new scavenger material has been tested and compared with that of the conventional scavenger material (i.e., triazine) based on the mechanical properties results and the amount of H2S gas captured. The compressive strength results clearly showed enhanced performance of Bent/ZIF-67 over the conventional scavenger material with an increase of 14-day and 28-day compressive strengths of around 8-10% at the optimal dosage of 0.05% BWOC (i.e., by weight of cement). The tensile strength showed even more remarkable enhancements of 25-45% over the conventional material at various concentrations of Bent/ZIF-67. This clearly supports the enhancement of cement matrix strength after the addition of this new material. The elastic property measurement showed that there are reductions of around 7.5% and increments of around 2.6% in Young's modulus and Poisson's ratios of the cement matrix after the addition of this proposed new material. Most importantly, H2S scavenging tests showed dramatic gains, where the breakthrough time of H2S was delayed from ∼12 min in neat cement to over an hour with Bent/ZIF-67, while the time to reach 2 ppm outlet concentration was extended to ∼3.8 h, outperforming triazine (∼2.9 h). These results confirmed that Bent/ZIF-67 significantly enhanced both mechanical strength and sour-gas resistance of cement, making it a promising additive for improving well integrity in H2S-rich reservoirs.