During the Well Test operation, critical information about the reservoir is acquired, allowing its characterization. In order to perform this activity and due to storage problems, all fluid produced at this exploratory phase is disposed to the atmosphere by burners. In some occasions the gas flare can go off, dispelling the gas without burning. It is called "cold flaring" and depending on the reservoir this might be a problem due the concentration of hydrogen sulfide (H2S) on the gas phase and environmental conditions, such as wind speed and direction. The H2S is a toxic and colorless gas, which is heavier than the air and soluble in both water and hydrocarbons. The limit of exposure is 10 ppm in atmosphere for an 8 work hours

The aim of this work is to present and analyze different case studies, varying in line H2S concentration, flow rate, wind speed and wind direction, using computational fluid dynamics techniques. The software FLUENT was used to run 15 different situations, with 48 simulations each, in order to determine safe conditions to flow the well.

Three different types of mesh with about 280000 cells each were used, depending on the wind direction. In each one of the simulations, the H2S plume with 10 ppm was analyzed and classified if it could be hazardous for the rig environment or not. As a result of this project, three charts were created showing the safe zones of operation depending on the gas and environmental conditions. After this study, several wind conditions that were considered dangerous are now safe, as example cases with high flow rate and low H2S ppm or low flow rate and high H2S ppm, reducing the down time due environmental conditions, ensuring that the work is being done in a safety zone.