H2S Scavenging Capacity and Rheological Properties of Water-Based Drilling Muds

Experimental Investigation of Using Manganese Monoxide as a Hydrogen Sulfide Scavenger for Aqueous Drilling Fluids

One of the most serious safety and health concerns during drilling oil and gas wells is the potential release of hydrogen sulfide (H2S) to the surface, exposing workers to high risks. Serious corrosion-related damage to handling equipment is also inevitable in the presence of H2S. Various H2S scavengers have been utilized, but each has its pros and cons; hence, research is continuing to develop an optimum and feasible scavenger. Since manganese monoxide (MnO) is a reactive metal oxide with high oxidation and absorption capabilities, it may have the potential to effectively scavenge H2S during drilling operations when included in drilling mud formulations. Consequently, the key aim of this work is to investigate the H2S scavenging performance of the aqueous drilling fluid containing MnO. This work studied the impact of MnO addition on the drilling mud's alkalinity, rheological behavior, filtration performance, and corrosion tendency. The experiments were also conducted for mud without a scavenger and a fluid containing the SourScav commercial scavenger, which serves as a benchmarking reference. The findings demonstrated that MnO performed exceptionally well for H2S scavenging where it boosted the aqueous mud's scavenging capacity from 84.3 to 426.2 mg of H2S/L of mud, showing more than 400% improvement relative to the base mud. Additionally, this scavenging performance is about 2.1 times higher than that of the commercial scavenger. As opposed to SourScav, MnO maintained the mud's pH at a safe level above 10. The addition of either MnO or SourScav did not weaken the mud rheology and provided practically satisfactory rheological parameters. Both SourScav and MnO marginally increased the formed filter-cake thickness from 2.9 to 3.9 mm with a slight increment in the filtrated volume but still within the acceptable limits. The corrosion test indicated the noncorrosive characteristics (i.e., the corrosion rate was nearly zero) of MnO and the commercial scavenger. This study illustrates the promising utilization of MnO as a cost-effective H2S scavenger, enhancing the efficiency and safety of drilling operations.

Improvement of Hydrogen Sulfide Scavenging via the Addition of Monoethanolamine to Water-Based Drilling Fluids

The release of the lethal hydrogen sulfide (H₂S) gas during the drilling of sour subterranean formations is of huge health and safety concern. Additionally, the contact of this corrosive gas with handling equipment might result in severe damages and significant economic losses. Accordingly, effective in situ scavenging of H₂S while drilling is very crucial. Thus, we report herein the addition of monoethanolamine (MEA) to water-based mud with the objective of improving the H₂S-scavenging efficacy of the mud. The H₂S-scavenging capacity was evaluated for the MEA-containing mud and compared with the base mud and fluids containing the commercial scavengers, SourScav and triazine. Also, the key mud characteristics including rheology, filtration properties, alkalinity, and corrosion rate were investigated in the presence and the absence of MEA, and the obtained results were compared to those of SourScav and triazine. The obtained experimental results revealed that the addition of MEA to the base mud significantly improved the H₂S adsorption capacity of the base mud by 117%, compared to 50 and 74% with the SourScav and triazine. Additionally, the pH value of the MEA-containing mud complied with the practical recommendations for drilling in a sour environment. Moreover, the plastic viscosity was increased by 13% to 37 cP with the MEA-containing mud with an insignificant impact on the yield point. Furthermore, the MEA-containing mud showed a favorable zero corrosion rate, as was the case for SourScav and triazine muds. However, unlike SourScav and triazine, MEA did not substantially enhance the filtration performance. Nonetheless, the filtration characteristics of the MEA-containing mud were still better than the base mud and within the recommended practical range for water-based muds. Overall, the results presented in this study reveal that the addition of monoethanolamine to water-based muds improves the mud characteristics and, more importantly, provides a superior H₂S-scavenging performance relative to SourScav and triazine scavengers, suggesting the commercial relevance of MEA for drilling applications.

Optimum Selection of H2S Scavenger in Light-Weight and Heavy-Weight Water-Based Drilling Fluids

During hydrocarbon drilling operations, the presence of hydrogen sulfide (H₂S) gas could cause serious health and safety issues. Scavenging this gas and eliminating its impact are essential requirements for a safe drilling operation. This study investigated the impact of three H₂S scavenger additives (copper nitrate, iron gluconate, and potassium permanganate) on water-based drilling fluids (WBDFs). The additives were tested on two actual field drilling mud samples that differ mainly in their weight. The scavengers' impact on drilling muds was investigated by measuring their scavenging capacity and their effect on rheology, fluid loss, and pH. Potassium permanganate outperformed the other scavengers when added to the lighter (lower density) WBDF. However, it did not impact the scavenging capacity of the heavier mud system. Copper nitrate outperformed the other scavengers in the heavier drilling mud system. Also, the addition of copper nitrate in the lighter mud system increased its H₂S-scavenging capacity greatly, while for iron gluconate, it did not perform very well. Overall, all the scavenger-containing drilling muds did not have any significant harmful impact on the plastic viscosity or the fluid loss properties of the drilling muds. Furthermore, all the tested drilling mud samples showed an excellent ability to clean wellbores and suspend drill cuttings evident by the high carrying capacity with the exception of iron gluconate or potassium permanganate with the heavy mud system.