Nanotechnology in hydrogen sulfide detection

Hydrogen sulfide (H2S) leaks can cause problems that affect both workers and equipment in the drilling industry. The explosive gas naturally occurs in oil and natural gas deposits. The lesser risk from H2S, corrosion of metal, paint, and epoxy, can be prevented with the use of special coating. The greater risk, the risk to the health of industry workers, can be prevented with detection equipment. More recently, nanotechnology has been tested to detect H2S in the air.

Presence in reservoirs

The presence of H2S in reservoir fluids is a major problem for the petroleum industry and is associated with reservoir souring, iron sulfide deposition, poor sweep efficiency, and increased corrosion. Its occurrence may cause the early abandonment of many oil and gas reservoirs by increased costs, reduced revenue, and environmental concerns. In many cases, reservoirs that initially did not contain sulfide have become sour as a result of operations. This progressive increase in sulfide levels is most notable in reservoirs that were flooded with seawater. (50980-PA)

Health effects of hydrogen sulfide

From http://www.safetydirectory.com/hazardous_substances/hydrogen_sulfide/fact_sheet.htm: H2S poses multiple health risks to people working around it, ranging from watery eyes to nausea or migraines, coma, and even death. The gas is classed as a chemical asphyxiant, in the same category as carbon monoxide and cyanide gases. It inhibits cellular respiration and uptake of oxygen, causing biochemical suffocation. Common exposure symptoms include:

Working with hydrogen sulfide

Most countries have legal limits in force that govern the maximum allowable levels of exposure to hydrogen sulfide in the working environment. A typical allowed exposure limit in multiple countries is 10 ppm. While the distinctive odor of H2S is easily detected, it causes olfactory fatigue, therefore one cannot rely on the nose as a warning device. The only way to accurately determine H2S exposure levels is to measure the amount in the air. With a vapor density of 1.19, H2S is about 20 percent heavier than air, so this invisible gas will collect in depressions in the ground and in confined spaces.

Traditional detection methods

Paper strips infused with lead acetate have been commonly used to measure air samples for H2S levels. This method has been improved upon by soaking the paper in mercuric chloride or silver nitrate. Mercuric chloride paper strips are sensitive and reliable for measurement of hydrogen sulfide in air with a sensitivity of 0.7 µg/L. Strips impregnated with silver nitrate are suitable for determining H2S concentrations in the range of 0.001–50 ppm. Potentiometric titration with a sulfide ion-selective electrode as an indicator has been used to measure hydrogen sulfide in the air at ppb levels. This method has been shown to have very good accuracy and precision. Passive card monitoring has been used to detect hydrogen sulfide in workplace environments. Badges worn in a worker’s breathing zone that change color based on exposure to toxic gases also detect hydrogen sulfide. The sensitivity for the hydrogen sulfide badges is 10 ppm/10 minutes with a color range of white to yellow, which indicates H2S presence. Other colorimetric methods for monitoring hydrogen sulfide include hand-held colorimetric tubes. Air is drawn through the tube and the presence of hydrogen sulfide reacts with a chemical reagent in the glass tube and causes a color change.

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