What Determines Sour Gas Reservoir Development in China
Authors: Guo Xiao , Du Zhimin , Fu DeKui 
Published: February 2016

Abstract
Sour gas reservoirs are abundant and has promising development prospects in South China, such as Fei Xian Guan group sour gas reservoirs of Luo JiaZai, Pu Guang, Du Kouhe, Tie Shanpo, Long Menchang and Gao Fengchang. The development of sour gas reservoirs will become increasingly more important for meeting the demand of civil natural gas market. However, considerable attention has been devoted to the dangers of hydrogen sulfide during different phases of the natural gas industry, including drilling, completion, development, work-over operations, processing and transportation due to high toxicity and corrosivity of hydrogen sulfide. The characteristics of complex flow through porous media on account of phase behavior variation and sulfur precipitation can also lead to difficulties in scientific studies and production management. In this presentation, an overview of development of sour gas reservoirs in South China was provided including sour gas sample PVT measuring, elemental sulfur deposition evaluation and technical and operational experience and lessons. This work will help improve future management and development of sour gas reservoir development in China and avoid failure in operations.

Introduction
Sour gas reservoirs are abundant and has promising development prospects in South China, such as Fei Xian Guan group sour gas reservoirs of Luo JiaZai, Pu Guang, Du Kouhe, Tie Shanpo, Long Menchang and Gao Fengchang. The development of sour gas reservoirs will become increasingly more important for meeting the demand of civil natural gas market. However, considerable attention has been devoted to the dangers of hydrogen sulfide during different phases of the natural gas industry, including drilling, completion, development, work-over operations, processing and transportation due to high toxicity and corrosivity of hydrogen sulfide. The characteristics of complex flow through porous media on account of phase behavior variation and sulfur precipitation can also lead to difficulties in scientific studies and production management.
Conventional EOS can not accurately and exactly predict gas compressibility, density, and viscosity, which are important properties in the calculations of gas flow through reservoir rocks, material balance calculations, and design of pipelines and production facilities. Li and Guo [1] studied the accuracy of Peng-Robison EOS to predict phase equilibrium of sour gases. Mohsen-Nia et al[2] introduced a two constant EOS, based on theoretical background of statistical mechanics, designed specially to predict properties of sours natural gases. Huron et al.[3] and Evelein and Moore[4] used SRK-EOS to study the hydrocarbon system containing hydrogen sulfide and carbon dioxide.
Sulfur precipitation is also an important phenomenon during sour gas production, as shown in Figure 1. Reduction in pressure and temperature induced sulfur precipitation by a reduction in the solubility of the sulfur in the gas phase beyond its thermodynamic saturation point. Sulfur precipitation can impair well productivity and thus the economics precipitation can impair well productivity and thus the economics of reserve depletion[5,6,7]. Kuo and Colsmann[8] developed the first mathematical model of a solid phase precipitation in porous medium and its influence on fluid flow. Roberts[9] have used a conventional black-oil reservoir simulators to model sulfur depositional processes and described significant flow impairment induced by sulfur deposition for a history match of the Waterton field case. Lately, Guo et al.[10] have presented a new gas-liquid-solid coupling model in fractured carbonate gas reservoir with high H2S-content, accounting for sulfur deposition, phase behavior variation, geochemical rock-water-gas interactions, adsorption. Abou-Kassem[11] studied numerically and experimentally the deposition of elemental sulfur in porous medium using gas and oil flow systems. Shedid and Zekri [12] conducted a detailed experimental study using a wide range of applied flow rates, different initial concentrations of sulfur and different rock permeability. Shedid et al[13] also carried out ten dynamic flow experiments using different crude oils of different sulfur and asphaltene concentrations and under different flow rates to investigate the simultaneous deposition of sulfur and asphaltene in porous media. Guo et al. [14] have presented a gas-liquid-solid mathematical model to predict sulfur deposition based on the characteristics of composition and phase behavior of gas-liquid system.