Study of CaSO4-C-H2O System: Simulation Experiments and Thermodynamic Assessment
详细信息
- 责任者：Ding Kangle (School of Chemistry and Environmental Engineering ; Yangtze University ; Jingzhou 434023 ; China) ; Luo Yue
- 刊名：Acta Geologica Sinica
- 出版年：2013
- 卷期：87(3)
- 关键词：热模拟 ; thermal simulation
- 页码：p.424-432
- 图表：illus., 2 tables, 57 refs.
- 分类号：1003
- issnNo：ISSN0001-5717
- isbnNo：CN11-1951/P
摘要
It has been traditionally believed that the TSR solid bitumens （pyrobitumen） are the direct product of thermochemical process and has less effect over the process of thermochemical sulfate reduction （TSR） compared with hydrogen sulfide （H2S）. In this study, thermochemical simulation experiment of the CaSO4-C-H2O system was conducted to investigate thermodynamic characteristics of STR in the CaSO4-C-H2O system using activated carbon （C） as a model compound of solid bitumen. The results show that CaSO4-C-H2O system initiated TSR process at the temperature of 300℃, generating products like CaCO3, H2S and CO2. The threshold temperature （300℃） is much lower than temperature range of the TSR simulation tests using hydrocarbons in both gaseous and aqueous states, and consistent with the result through thermodynamic calculations. Process simulation of TSR was conducted using the software of HSC Chemistry 5.0. It was found that TSR in the CaSO4-C-H2O system initiated at reservoir temperatures of 25200℃ was completely controlled by kinetic factors and increasing pressure is unfavorable to initiation of TSR under a constant temperature. The intensity of TSR is likely associated with saturation concentration of CaSO4 in water: a small amount of water may contribute to better oxidizing conditions while excessive water likely restrains the process of TSR. Under the conditions of pH≤2 and certain temperature, amount of sulfate decreased with decreasing pH. However, for pH range （pH>4） formation water in sedimentary basins, effect of pH on TSR can be negligible. TSR in the system of CaSO4CH2O is an exothermic process, and the reaction heat increases with the increasing temperatures. It was established that reaction heat of TSR is about 12.9 133 J/mol CaSO4 at 25200℃. Thermodynamic studies and experimental results imply that solid bitumens （pyrobitumen） are much easily involved in TSR than gaseous or aqueous hydrocarbons.
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