Abstract
The deposition of elemental sulfur as a solid phase will result in plugging the pore space available for gas flow and reduce the reservoir productivity. Elemental sulfur also can be deposited as a liquid phase if the reservoir temperature was greater than 115°C. The liquid sulfur will not flow at the same velocity as gas and in turn the gas flow will be restricted by the settled sulfur due to the huge difference between the liquid sulfur density and gas (Could be 20 times or more in certain cases). For the isothermal conditions in the reservoir, the reduction in reservoir pressure below a critical value will cause the elemental sulfur to deposit in the formation, and in turn the gas well productivity will be affected. Accurate prediction of sulfur deposition in the reservoir will help in better manage sour gas reservoirs with potential sulfur deposition problems.
In this paper new analytical and numerical models were developed to predict the effect of sulfur deposition on the damage of the near-wellbore. The damage will be quantified through the investigation of the effect of sulfur deposition on the skin damage value, relative permeability of the gas phase, and the change in rock wettability due to sulfur deposition especially in the near-wellbore region. The main objective of these models is to investigate the effect of radial distance on formation damage. Different rock and fluid properties accurate correlation were used in this model for better results prediction. Previous studies did not consider the change in gas properties with pressure, and numerically modeled the sulfur deposition as a condensate in a gas condensate reservoir. In this paper will consider r the sulfur adsorption and the actual physical properties of the sulfur will be used in the developed model. The optimum gas flow velocity will be determined based on the sulfur solubility.
Analytical and numerical solutions show that the deposition of sulfur was affected by the radial distance from the wellbore and sulfur solubility change as a function of the pressure drop. The numerical and analytical models showed good match in modeling the sulfur deposition in the near-wellbore area. Sulfur deposition was found to have a great effect on the rock wettability, and in turn the gas production will be affected. The model can be used to predict the critical flow velocity that the gas can flow without precipitating sulfur. The optimum gas flow velocity was estimated to be a range that maximizes the sulfur solubility in the gas.
