Experimental and numerical modeling of sulfur plugging in a carbonate oil reservoir

Many oil and gas reservoirs in the United Arab Emirates produce large amounts of sour gas, mainly in the form of hydrogen sulfide. In addition to creating problems in the production line, wellbore damage is often reported due to the precipitation of elemental sulfur in the vicinity of the wellbore. While there have been several studies performed on the role of solid deposition in a gas reservoir. However, the possibility of sulfur deposit in oil reservoirs has not been investigated in the past. This paper presents experimental results along with a comprehensive wellbore model that predicts sulfur precipitation as well as plugging. The experiments are conducted in a core (linear system). Both analytical and numerical modeling are performed in a linear coordinate system. Data for the numerical model are obtained from both test tube and coreflood experiments. By using a phenomenological model, the wellbore plugging was modeled with an excellent match (with experimental results). The crude oil was de-asphalted prior to conducting the experiment in order to isolate the effect of asphaltene plugging. A series of coreflood tests was carried out to observe sulfur precipitation and plugging in a carbonate rock. Significant plugging was observed and was found to be dependent on flow rate and initial sulfur concentration. This information was used in the phenomenological model that can be incorporated in the wellbore numerical model.