Study on sulfur deposition damage model of fractured gas reservoirs with high-content H2S

Due to extreme poison, strong corrosion, and complex precipitation and deposition of H2S in the reservoir, it is very difficult and risky to investigate and explore drilling, completion, production and gas transportation. In the course of production of fractured gas reservoir with high H2S content, formation pressure falls continually, which lead to decline of solubility of sulfur particles in gas phase. Sulfur particles which dissolve in gas phase originally in the formation should precipitate from gas phase after running up to saturation state and deposit at pore space and throat, sequentially resulting in formation porosity and permeability reduction. At present, the researches of sulfur deposition are mainly focused on the conventional gas reservoirs and sulfur deposition in the near wellbore region is generally estimated using Roberts' model. However, most of the gas reservoirs with high-content H2S are fractured gas reservoirs, classical damage model is no longer applicable to fractured gas reservoirs with high H2S content. In the present study, a sulfur deposition damage model is established. The refined model, based on non-Darcy flow, takes into consideration the effects of sulfur deposition, variation in gas properties and fracture. In addition, the effect of gas well production rate on formation permeability is also studied. The results show that formation permeability decreases with fracture aperture and gas well production rate increasing. The bigger gas well production rate is, the quicker sulfur precipitates. The sulfur deposition of fractured gas reservoir with high-content H2S is mainly in the near wellbore zone, and the fracture aperture has a significant impact on the formation permeability in the near wellbore zone.