Clearing the Air on Hydrogen Sulfide

Hydrogen Sulfide (H₂S) is present at dangerous concentrations across a substantial share of global oil and gas operations and processes. This colorless, flammable, highly toxic inorganic gas naturally occurs. But it is highly corrosive to equipment, and acutely toxic to humans and animals, and environmentally damaging to air, water, and soil. Its presence influences reservoir development, facility design, worker safety, gas processing, sulfur recovery, and environmental management throughout the oil and gas supply chain.

H₂S Impacts

Not only is H₂S dangerous to people and animals, but it is also deadly at high levels. For workers without proper training and equipment, the gas can rapidly become fatal. In a 2004 study, 21% of worker fatalities were found to have come from “good Samaritans,” i.e., coworkers trying to help a fallen colleague only to succumb to the gas themselves.

H₂S emitted into the air reacts in the atmosphere to form sulfur dioxide and cause acid rain. High H₂S levels in soil harm plant life and reduce crop yields. When dissolved in water, H₂S contaminates rivers, lakes, and groundwater, tainting drinking water and creating a toxic environment for aquatic life.

The acid formed when H₂S readily dissolves in water is corrosive to industrial equipment that the industry relies on to prevent damaging leaks and dangerous fugitive emissions. An estimated 40% of all corrosion in the oil and gas industry is due to H₂S. This corrosion leads to worker and environmental risk. Not only do the resulting leaks pose imminent risk to human health, the methane released as a result of equipment corrosion exacerbates climate change and leads to energy loss.

Workers in the oil and gas industry are routinely trained to recognize H₂S hazards, respond to gas alarms, and evacuate or take other protective actions when dangerous concentrations are detected. At concentrations above 100 parts per million (ppm), or 0.01% of the air they are breathing, H₂S will irritate the respiratory system and poison human cells, preventing them from using oxygen effectively. At concentrations above 200 ppm, a person’s sense of smell is rendered ineffective quickly, so a person’s natural awareness of the gas is gone. At concentrations above 500 ppm, workers collapse and the gas kills them within an hour.

Fate of H₂S in the Oil and Gas Supply Chain

H₂S may be present as a gas or be dissolved in the produced oil, condensate, and water at the wellsite. H₂S can be generated or introduced into petroleum reservoirs when heat, bacteria, and pressure decompose sulfur-rich organic matter to form H₂S over time. The introduction of bacteria during oil and gas production via water injection or in fields with declining pressures can also release H₂S after production starts and as fields age.

H₂S must be removed from the oil and gas supply chain both during gas processing before oil and gas are transported and during refining when petroleum products are manufactured.

At the gas-processing plant, sour gas undergoes sweetening, meaning H₂S and often carbon dioxide is removed from the natural gas. Sweetening takes concentrated H₂S and converts it into elemental sulfur at a sulfur recovery plant. Alternatively, a unit at the gas processing plant injects H₂S underground or sends it to be flared or incinerated. Flaring or incineration, however, does not eliminate the sulfur; combustion converts most of the H₂S into sulfur dioxide (SO₂), another harmful air pollutant. By the time natural gas enters a pipeline, most H₂S must be removed at a gas-processing plant so the gas meets the receiving pipeline’s quality requirements to prevent corrosion. Oil refineries also remove embedded H₂S from the petroleum products—using sulfur recovery plants or incineration at the refinery.

Tracking H₂S Concentrations

Dangerous H₂S concentrations can occur through the oil and gas supply chain at key process stages. While concentrations can vary widely by oil and gas reservoir, chemical process, and operating conditions, they generally increase as H₂S becomes more concentrated as it moves through processing stages before being minimized in pipelines that ship finished petroleum products to customers.

Analyzing H₂S Data

RMI’s Oil Climate Index plus Gas (OCI+) is an open-source analytic tool that estimates and compares the life-cycle greenhouse gas emissions from equivalent barrels of oil and gas. Over 70% of global supply is modeled, from extraction through consumption. RMI inputs concentrations of H₂S as one of the many variables to model overall oil and gas emission intensities.

In addition to reporting emissions intensities, RMI maps our results on the OCI+ web tool. A new H₂S risk map has been developed to indicate how this dangerous molecule plays a role in our energy future. This map is only as good as the data underlying it, however. H₂S data is frequently missing or unreported, leaving the public in the dark about major risks in their own backyards.

H₂S Incident Trends

RMI analyzed five decades of workplace incident records from the US Occupational Safety and Health Administration (OSHA) to understand where H₂S-related incidents occur across the oil and gas industry supply chain, from production, gas processing, and refining, and transport.

The analysis revealed a persistent pattern: wellsite production operations and oil refineries consistently experience higher H₂S incident risk than gas processing and transmission operations. These findings show that H₂S remains a persistent safety challenge despite decades of industry experience and the widespread adoption of H₂S detection, monitoring, and training programs.

Why this matters to protect people and property

RMI analysis reveals that dangerous concentrations of H₂S are present across a substantial share of oil and gas operations. The findings highlight the persistent challenge of managing H₂S hazards over the past five decades despite the widespread adoption of safety protocols.

Given these known, persistent risks, the oil and gas industry has been tasked with safely managing H₂S for decades. Technologies have been developed to handle high-H₂S oil and gas responsibly with low leakage. Extending these best practices across all oil and gas operations can safeguard both human health and the climate.

The next step in the path towards a cleaner energy future resides in greater transparency in H₂S occurrence, varying concentrations, and field souring. Local communities and oil and gas workers have the right to understand the risks they face, and decision makers need the data to make informed and intelligent decisions to protect people and the environment.