The Importance of Elemental Sulphur, Mercury and Condensate Identification in Sour Gas Field Development Project: Case Study

Abstract

The elemental sulfur deposition is a potential risk in gas field production especially during offshore gas early development stage since it is related to economical issues. Later on, when elemental sulphur finally deposited, it is a serious concern during production as it can result in various significant flow assurance, safety, operational, corrosion and integrity problems. Sulphur solubility in gas wells can be affected by a number of conditions including, but not necessary limited to their origins, gas composition, pressure, temperature and the amount of condensate present. These include elemental mercury, ammonia, carbon sulphides and mercaptans. It is noticed that sulphur is not only physically soluble in gas or condensate but also can be chemically bonded to H2S. The paper objective is to explain a novel work flow of elemental sulphur, mercury and condensate identification, bottom hole sampling process, solubility curves prediction and treatment mitigation during initial gas field development project as a case study especially during facilities concept development. The sets of correlation process are applied as screening to predict elemental sulfur deposition risk. The physical solubility of sulphur in a natural gas increases with the pressure and the density of the gas phase but is limited by spatial interactions between molecules. However, it decreases with the temperature because low energy interactions are broken by thermal agitation. In offshore environment particularly, the physically dissolved sulphur in a natural gas is sensitive in responds to changes in pressure and temperature; its precipitation will occur as soon as saturation conditions are reached along the production pathway from wells to onshore receiving facilities. As summary, the elemental sulphur deposition for lean (< 1% C2+), sour gas containing H2S is viable and has higher risks compared to similar sour gas with condensate field, while the elemental sulphur and mercury cannot co-exist in the reservoir and in the same time, anhydrites must be present in the formation for elemental sulphur to be present.