Thermodynamics of Diagenetic Fluid and Fluid/Mineral Reactions in the Eogene Xingouzui Formation, Oil Field T, Jianghan Basin

摘要

This study focuses on the thermodynamics of diagenetic fluid from the Eogene Xingouzui Formation which represents the most important reservoir in Field Oil T in the Jianghan Basin. The measured homogenization temperatures (110-139℃) of fiuld inclusions in diagenetic minerals fall within the range of 67- 155℃ at the middle diagehetic stage. The pressure of diagenetic fluid is estimated at 10.2-56 MPa. The activity of ions in the fluid shows a tendency of Ca2+ > Mg2+ > Na+ > K+ > Fe3+ > Fe2+ for cations, and HCO3 > SO4- > F- > Cl- >CO2-3 for anions. For the gaseous facies, there is a tendency of CO2> CO> H2S>CH4> H2. According to the thermodynamic calculations, the pH and Eh of the fluld are 5. 86 - 6. 47 and -0.73-0.64V,respectively. As a result of the interaction between such a diagenetic fluid and minerals in the sediments, feldspars were dissolved or alterated by other minerals. The clay mineral kaolinite was instable and hence was replaced by illite and chloritoid.