H 2 S Scavenging Capacity and Rheological Properties of Water-Based Drilling Muds.

Drilling hydrocarbon formations where hydrogen sulfide (H ₂ S) is present could lead to the carryover of H ₂ S with the drilling mud (i.e., drilling fluid) to the surface, exposing working personnel to this lethal gas. Additionally, H ₂ S is very corrosive, causing severe corrosion of metal parts of the drilling equipment, which in turn results in serious operational problems. The addition of an effective H ₂ S scavenger(s) in the drilling mud formulations will overcome these health, safety, and operational issues. In this work, zinc oxide (ZnO), which is a common H ₂ S scavenger, has been incorporated into water-based drilling mud. The H ₂ S scavenging performance of this ZnO-containing drilling mud has been assessed. Additionally, drilling mud formulations containing either copper nitrate (Cu(NO ₃ ) ₂ ·3H ₂ O) or potassium permanganate (KMnO ₄ ) have been prepared, and their H ₂ S scavenging performances have been studied and compared to that of the ZnO-containing drilling mud. It has been observed that the scavenging performance (in terms of the H ₂ S amounts scavenged up to the breakthrough time and at the saturation condition) of the ZnO-containing drilling mud is very poor compared to those of the copper nitrate-containing and KMnO ₄ -containing drilling muds. For instance, the amounts of H ₂ S scavenged up to the breakthrough time by ZnO-containing, copper nitrate-containing, and KMnO ₄ -containing drilling muds were 5.5, 15.8, and 125.3 mg/g, respectively. Furthermore, the amounts of H ₂ S scavenged at the saturation condition by these drilling muds were, respectively, 35.1, 146.8, and 307.5 mg/g, demonstrating the superiority of the KMnO ₄ -containing drilling mud. Besides its attractive H ₂ S scavenging performance, the KMnO ₄ -containing drilling mud possessed more favorable rheological properties [i.e., plastic viscosity (PV), yield point (YP), carrying capacity of the drill cuttings, and gelling characteristics] relative to the base and the ZnO-containing and copper nitrate-containing drilling muds. The addition of KMnO ₄ to the base drilling mud increased its apparent viscosity, PV, and YP by 20, 33, and 10%, respectively. Additionally, all tested drilling muds possessed acceptable fluid loss characteristics. To the best of our knowledge, there are so far no published studies concurrently tackling the H ₂ S scavenging (i.e., breakthrough time, breakthrough capacity, saturation time, saturation capacity, and scavenger utilization) and the rheological properties of water-based drilling muds, as demonstrated in the current study, highlighting the novelty of this work.
Competing Interests: The authors declare no competing financial interest.
(© 2020 American Chemical Society.)