Oil-based drilling mud comprising biosurfactant and hydrophobic zinc nano-powders with excellent H2S scavenging performance

Hydrogen sulfide (H2S) could be released during the drilling operations of oil and gas wells. The release of this lethal gas to the surface will expose the working personnel to high safety and health risks. Additionally, the contact of this very corrosive gas with handling and processing equipment will result in severe economic losses. Despite such serious issues, formulating and testing oil-based muds (OBMs) with H2S scavenging capability is still lacking in the literature. Thus, the key aim of this study is to formulate invert emulsion diesel-based drilling mud (abbreviated as IEDBM) that is capable of effectively scavenge H2S in-situ once it is encountered. This aim is realized through the addition of a small quantity of potassium permanganate to the formulated IEDBM. According to the obtained results, the inclusion of a small amount of potassium permanganate (i.e., 1 wt.%) can scavenge up to 0.43 and 0.71 kg H2S per barrel of the formulated mud at the breakthrough (i.e., 29.8 h) and saturation (i.e., 86.2 h) times, respectively. The IEDBM was stabilized using Span 80 (a non-ionic surfactant) and rhamnolipid anionic biosurfactant. The IEDBM also comprised hydrophobic zinc nano-powders (contact angle with water similar to 105 degrees) as weighting agent. The application of rhamnolipid biosurfactant and hydrophobic zinc nanopowders in drilling formulations is another novel aspect of the work reported herein. The shear rate-shear stress data were well fitted using the Bingham plastic, Casson, and Herschel-Bulkley models. The apparent viscosity of the IEDBM was investigated under different shear rates and the obtained results showed a sharp drop in the mud apparent viscosity with increasing the shear rate up to 40 s(-1), followed by a slower decrease upon the further increase in the applied shear rate; which is in line with those of OBMs reported in the literature. The effect of temperature on the apparent viscosity of the IEDBM was also investigated; the change in the mud viscosity was found to be inversely proportional to temperature in almost a linear fashion. The results presented in this work reveal the high potential of formulating OBMs with effective H2S scavenging performance and appropriate flow properties.