江汉盆地 T 油田新沟嘴组成岩流体及流体/矿物反应热力学

THERMODYNAMICS OF DIAGENETIC FLUID AND FLUID/MINERAL REACTION IN THE EOGENE XINCOUZUI FORMATION,OIL FIELD T,JIANGHAN BASIN

对江汉盆地 T 油田主要的工业储层——下第三系新沟嘴组沉积岩石的成岩流体进行了热力学研究。实测的成岩矿物流体包裹体的均一温度为110—139℃,属于该区中成岩阶段的温度范围(67—155℃)。成岩流体的压力为10.2—56MPa。成岩流体中阳离子的活度出现 Ca^(2+)>Mg^(2+)>Na^+>K^+>Fe^(3+)>Fe^(2+);阴离子的活度出现 HCO_3^->SO_4^(2-)>F^->Cl^->CO_3^(2-);气相成分出现 CO_2>CO>H_2S>CH_4>H_2的变化趋势。热力学计算表明,成岩流体的 pH 值为5.86—6.47,Eh 值为-0.73V—-O.64V。这种成岩流体与沉积岩中矿物发生化学反应后,可导致长石的溶蚀或被其它矿物交代,以及粘土矿物高岭石不稳定而向伊利石和绿泥石转化。

This study focusses on the thermodynamics of diagenetic fluid from the EogeneXingouzui Formation which represents the most important reservoir in field oil Tin the Jianghan Basin.The measured homogenization temperatures(110—139℃)offluid inclusions in diagenetic minerals fall within the range of 67—155℃ at themiddle diagenetic stage.The pressure of diagenetic fluid is estimated at 10.2—56MPa.The activity of ions in the fluid shows a tendency of Ca^(2+)>Mg^(2+)>Na^+>K^+>Fe^(3+)>Fe^(2+) for cations,and HCO_3^->SO_4^(2-)>F^->Cl^->CO_3^(2-)for anions.For the gaseous facies,there is a tendency of CO_2>CO>H_2S>CH_4>H_2.Acco-rding to the thermodynamic calculations,the pH and Eh of the fluid are 5.86—6.47and—0.73V—0.64V,respectively.As a result of the interaction between such adiagenetic fluid and minerals in the sediments,feldspars were dissolved or alteratedby other minerals.The clay mineral kaolinite was instable and was replaced by illi-te and chloritoid.