EOS-Related Mathematical Model To Predict Sulfur Deposition And Cost-effective Approach Of Removing Sulfides From Sour Natural Gas

Abstract

Abstract Sulfur deposition in the formation, the vicinity of the wellbore and the production line, may significantly reduce the inflow performance of sour gas wells and increase operation cost. The work of sulfur deposition prediction and removal are increasingly performing in sour natural gas reservoirs of South China. In this paper, a gas-liquid-solid mathematical model to predict sulfur deposition, has been developed based on the characteristics of composition and phase behavior of gas-liquid system. i.e., the phase behavior of gas-liquid system is calculated in light of EOS, and the elemental sulfur is considered as a non-ideal solid described by virtue of regular solution theory. The EOS-related mathematical model proved to successfully match and predict sulfur deposition via some test examples. In addition, two formulated desulphuring agents of sulphone-amine solution and MDEA reinforcing solution are presented based on the solubility of H2S, CO2 and their mixture in water. The influences of operation conditions and other factors on desulphuring agents were investigated through both indoor and industrial experiments, and the results indicated that these two formulated desulphuring agents could effectively increase the rate of removing sulfur and also overcome the problems encountered during microbial oxidation of removing sulfides. The preliminary work can help engineer evaluate accurately sulfur deposition and remove effectively sulfides so that the impact of sulfur deposition on gas production is minimized during the development of sour natural gas reservoirs. Introduction In recent years, the search for natural gas has yielded many reserves that contain high concentrations of hydrogen sulfide, so-called sour gas reservoirs. Production of sour gas initially was on a limited scale but since has increased considerably as a result of price increases for fossil fuels. It is well known that sulfur is soluble in sour gas and often precipitates during production if the temperature and pressure decrease. Sulfur precipitation can impair well productivity and thus the economics precipitation can impair well productivity and thus the economics of reserve depletion[1,2,3]. Otherwise, it is significantly important to control and remove of sulfides nearby wellbore and along gas production pipeline. Many studies were focused on sulfur production and/or deposition in gas/oil wellbore holes, especially of gas reservoirs[4,5]. Kuo and Colsmann[6]developed the first mathematical model of a solid phase precipitation in porous medium and its influence on fluid flow. Roberts[7] 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. [8] 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[9] studied numerically and experimentally the deposition of elemental sulfur in porous medium using gas and oil flow systems. Shedid and Zekri [10] 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[11] 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.