Deposition of solid elemental sulfur in the formation may significantly reduce the inflow performance of sour-gas wells. The key operational and reservoir parameters that influence the magnitude of impairment by sulfur deposition were identified through the derivation of an analytical expression for the rate of sulfur buildup assuming idealized flow conditions. A methodology for the use of conventional, black-oil reservoir simulators was subsequently developed to permit the investigation of sulfur-deposition processes for specific reservoir descriptions and well operations. The rate of sulfur buildup in the formation was shown to be inversely proportional to the square of the radial distance from the well. As a consequence, the magnitude of sulfur deposition is highly sensitive to well skin the lower the skin, the farther away from the well the deposition occurs and the lower the sulfur-buildup rate. Nonuniform deposition over the pay interval (owing to reservoir layering or uneven stimulation) was shown to accelerate the impact of sulfur deposition. A field case involving early decline in well production caused by sulfur deposition was successfully history-matched with the simulation model developed in this study.
Elemental sulfur is often present in appreciable quantities in sour gas at reservoir pressure and temperature conditions. Reduction of pressure and temperature generally reduces the solubility of sulfur in sour gas. Once the reservoir fluid has reached a sulfur-saturated state, further reductions in pressure and temperature will cause sulfur to deposit. Many of the operational and reservoir parameters that influence sulfur deposition have been identified by Hyne. Effective solvents for the removal of sulfur deposits have also been reported.
Most of the reported investigations related to sulfur deposition have focused on deposition in the well, while few studies have been reported on the effect of deposition within the formation. In a theoretical study, Kuo investigated the effect of the deposition of immobile elemental sulfur from a homogeneous reservoir with a fluid containing 78% H2S and an estimated sulfur content of 120 g/m3.