Modeling of the change of rock petrophysical properties due to sulfur deposition in sour gas reservoirs

Deposition of sulfur as a solid phase will result in plugging the pore space available for gas flow and reduce the reservoir productivity. 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. Sulfur deposition can cause severe loss in the pore space available for gas, and in will affect the gas well productivity. In this paper a new analytical was 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 reservoir porosity, permeability, relative permeability, and the change in rock wettability due to sulfur deposition especially in the near-wellbore region. The developed model considered the change in reservoir gas properties with the change in reservoir pressure which has been neglected by previous investigators. 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. Coreflood experiment was performed to determine the effect of sulfur deposition on the carbonate rock permeability, porosity, and wettability. The experiment was used to determine the effect of sulfur adsorption on the rock petrophysical properties. Model predictions showed that sulfur deposition depends on the radial distance from the well bore. The analytical model can be used to predict the sulfur deposition in the near-wellbore region. Sulfur deposition was found to have a great effect on the rock wettability, and in turn the gas production will be affected. It was confirmed experimentally that the sulfur deposition reduced the carbonate core porosity, permeability, and changed the contact angle. The contact angle increased which means sulfur adsorption on the rock surfaces changed the rock towards more gas wet rock.