Sulfur Deposition Mechanism And Its Effect On Gas Well Productivity In Sour Gas Reservoir

With the increasing demand for natural gas in the world,the status of sour gas reservoirs is becoming more and more prominent in the production of whole natural gas industry.The sour natural gas resource of China is aboundant,mainly distributed in the provinces of Sichuan and Chongqing.After the sour gas well are brought on steam,the sedimentation of sulfur in the stratum will cause the occlusion of pores,the decrease of stratum permeability,which exerts an effect on gas productivity and can even make the well out of production.Thus,the investigation of the effect of sulfur sedimentation on the productivity of sour gas well is of great practical significance.Focusing on D sour gas reservoir and through the analysis of dynamic and static data of this gas reservoir,this paper researches on the sulfur sedimentation mechanism of sour gas reservoir and the productivity of the gas well.Firstly,through the analysis of the mechanism of the physical and chemical sedimentation and the occlusion of pores caused by elemental sulfur,the main sedimentation type of D gas reservoir with high sulfur content is figured out to be the physical deposition of solid elemental sulfur.Secondly,by investigating the algorithm of PVT parameters in the sour gas reservoir,the calculation of PVT parameters which is fit for the gas reservoir with high sulfur content in the east of Sichuan province is explicit.Through studying the prediction model of sulfur solubility in the natural gas,the prediction model of sulfur deposition saturation are established,the strata are divided into hydrodynamic scour broken down area,hydrodynamic carrying sulfur area,stable sulfur deposition area,weak sulfur deposition area(or non sulfur deposition area),and the occlusion predicting model of sulfur deposition are derived.Thirdly,the arithmetic of sulfur saturation in sour gas reservoir strata are confirmed by resolving the mathematic model of the fluid penetration in the strata and the prediction model of sulfur saturation under the influence of sulfir deposition and analyzing the impact of sulfur deposition to reservoir property such as porosity and permeability.At last,the productivity formula of gas well under the influence of sulfur deposition is derived,and analyzing the effect of sulfur deposition on the gas well productivity.The analysis of the actual examples indicates that the non Darcy seepage radius mainly distributed in the range of 0.2-46.46m,that the sulfur deposition occlusion occurs mainly in the hydrodynamic sulfur carrying region where the radius to the well bottom is 2-4m and the impact of sulfur deposition on stratum porosity and permeability in the early stage of production reaches a maximum,witch have a positive correlation with the yield.