Can oil and gas operations generate H2S?
Workers in the oilfields around Midland must be aware of the dangers of hydrogen sulfide. Many of the wells and facilities that they will work on will naturally contain some amount of the toxic gas. Current industry standard is to consider the operation as having H2S or not based on previous measurements. Today we are concerned about the issue of new H2S generation especially in locations that were not previously known to contain the gas. There are several methods that hydrogen sulfide may be generated in a non-H2S area.
H2S Generating Environments
There are two types of environments that we consider for the potential to generate H2S. The first type of environment is known as anaerobic and organic. Anaerobic means the area has low oxygen, or poor airflow. Organic means that there has been an accumulation of dead material in the area. When these conditions are met, the introduction of sulfur reducing bacteria can generate hydrogen sulfide as the organic material is broken down and the gas accumulates.
The other type of environment is one that contains sulfur in the presence of an acid. Sulfur is an element found in the earth’s crust and also within living things. Sulfur can be found in abundance in many crude oils. Acids are substances which tend to give off extra hydrogen when they are placed in water. The combination of acids and sulfur often generates hydrogen sulfide in addition to organosulfur compounds (mercaptans).
One area that is commonly organic and anaerobic is within the oil and gas reservoir itself. Even so, many oil and gas reservoirs around Midland never developed hydrogen sulfide naturally because there was no presence of sulfur reducing bacteria to generate it. Over time, after the reservoir has depleted, the operator may choose to inject water to increase production. The water injection may carry bacteria with it. Now reservoirs that once had no hydrogen sulfide begin actively generating the gas from the bacteria in-situ.
There have been occasions when acid, such as hydrochloric acid, is pumped into an oil and gas well to clear some blockage. If the blockage contains iron sulfide scale, we now need to consider the effect of the acid on the scale. These scales contain sulfur and may release some H2S when mixed with a strong acid such as HCl. It is important to take some H2S precautions around non-H2S wells especially when using strong acids.
Bacteria at surface
During oil and gas production and processing we may also witness the creation of H2S at surface. There are cases where tanks and process vessels begin generating more and more H2S. This can be caused by bacteria within the tanks that continue to reduce the sulfur containing petroleum into hydrogen sulfide. Clearing the tanks and adding a biocide may be considered in these cases. Remember that hydrogen sulfide tends to be corrosive and can embrittle metals. Make sure to stay safe and consider these hydrogen sulfide issues when you are working in the oilfields around Midland Texas.