What Happens When a Sweet Well is Actually Sour?

Posted on August 16th, 2021
Posted in Uncategorized   

An important factor in the selection of a well site is the potential presence of hydrogen sulfide (H2S), which can lead the operations to be categorized as sour service if the H2S is above a certain threshold. Well economics are so adversely affected by the additional requirements of sour service that some operators elect to avoid drilling any wells that have the potential to be sour, while others aim to mitigate the adverse conditions of sour service through the use of biocides or other costly treatment techniques.

For operators that know they are drilling sour wells, additional design elements are usually implemented to manage the corrosive environment, including PWHT, internal coating or increased corrosion allowance on piping and equipment. Product specifications and / or SO2 emissions limits often require the removal of H2S; this can be accomplished with scavengers, but higher sulfur contents necessitate the use of a sulfur recovery technology.  In some situations, product specifications can be met by dilution with other sweet wells. Safety measures, such as H2S detection and maintenance procedures, are also employed to protect operations personnel. As a known entity, engineering can reduce the risk associated with sour service.

In some cases, either through inaccurate preliminary compositional data or through compositional changes as the well ages, a well that’s expected to be sweet can become sour, and surface facilities can be constructed that are not designed to handle sour service. Action is often required based on midstream contracts limiting H2S concentrations or SO2 emission limits. Other factors that may determine if action is needed are H2S concentrations, operating conditions, company safety protocols, risk tolerance, intended facility life, and the physical properties of the production fluids.

Awareness and front end engineering can help mitigate these risks through evaluation of pipe specifications to determine the maximum recommended H2S concentration in a given system, integration of tie points for future treatment options into the facility design, or adjustments to high risk parts of the process.