H2S will have no adverse effects on the mud. However, the gas is highly poisonous and corrosive.
Sources of H2S
The gas is sometimes associated with formation fluids. (Add Biocide)
Diagnosis
Gas liberated at surface will be detected by gas sensors.
Soluble sulphides in the mud are detected by use of the Garret Gas Train. The Mud Engineer must be familiar with its use and make sure that the equipment is called out and maintained in good working order when H2S presence is expected. Refer to the manufacturer’s instructions for detailed test procedures.
Treatment
1. pH must be raised to a level in excess of 10 using caustic.
2. Add a H2S scavenger such as zinc carbonate.