Abstract

Sour gas reservoirs with high content of sulfur are distributed widely around the world. Solid elemental sulfur which dissolves in the gas phase originally in the reservoir, may deposit when the thermodynamic conditions of the temperature, pressure or composition changes in the process of production. Deposition of solid elemental sulfur may block the pores in the formation and significantly affect the gas deliverability. In this paper, sulfur deposition mechanism is analyzed in the reservoirs. Based on the characteristics of sulfur deposition in the formation, a corrected function is introduced to modify the gas flow. Then, an evaluation method of the effect of sulfur deposition on gas deliverability is presented. For a practical sour gas reservoir, the gas deliverability considering sulfur deposition in formation is calculated and evaluated. The results show that the decrease degree of gas deliverability is different and it depends on the physical parameters in the formation on which the gas well is located.

Introduction

Because of the high content of sulfur, especially when the concentration of H2S is high in the reservoir fluid, the critical production technology is required. Reduction of pressure and temperature of reservoir which reduces the solubility of sulfur in sour gas will cause sulfur to deposit in the reservoir. Deposition of sulfur within reservoir rocks can impair porosity and permeability and results in the decline in gas productivity and thus affects economic feasibility negatively. Many of the operational and reservoir parameters influence sulfur deposition. A theoretical research was studied by Kuo[2] on investigating the effect of the deposition of immobile elemental sulfur from a homogeneous reservoir. Sulfur deposition in the formation was attributed to the decline in production from a well producing from a dry, sour (16% H2S) gas pool operated by Shell Canada Limited located in the Waterton gas field of south-west Alberta, Canada. Sour gas reservoirs with large amount of hydrogen sulfide, 7.13%-10.49% (102.07–196.57g/m3), Sulfur are found and developed in recent years in China, such as gas reservoir of Fei Xian Guan, Luo Jia Zai, located in Sichuan province. The distribution of sulfur in a core is illustrated in Fig.1.[1] In this paper, the focus is on the prediction of deposition of sulfur and reduction of gas productivity in order to assess the impact of sulfur deposition on inflow performance.

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