摘要
基于对反应过程吉布斯自由能增量的计算,探讨了长石的3种端元组成(钾长石、钠长石和钙长石)溶解生成高岭石、伊利石的热力学性质。结果表明:钾长石、钠长石和钙长石在成岩过程中均可以自发地向高岭石、伊利石转化。在长石的这3种类型中,钙长石溶解反应的吉布斯自由能增量最低,并明显具有正的温度效应,说明钙长石最不稳定且在低温条件下更易溶解;钾长石溶解反应的吉布斯自由能增量最高,并具有较大的负的温度效应,说明钾长石稳定性较高且在埋藏成岩条件下更易溶解;钠长石溶解反应的吉布斯自由能增量中等,受温度影响不大,但温度升高时其稳定性仍有所下降。与温度相比,压力对反应的吉布斯自由能增量几乎没有影响。因此,砂岩中的次生孔隙,尤其是埋藏成岩过程中形成的次生孔隙应与钾长石的关系最为密切,其次是钠长石,但其可能受到蒙皂石向伊利石转化反应的缓冲,在埋藏成岩条件下溶解较为困难,并可能造成斜长石的钠长石化或自生钠长石的沉淀。
Based on the calculation of Gibbs free energy increment （AG） for the reactions involved dissolution of three end-members of feldspar （K-feldspar, albite and anorthite） to form kaolinite or iUite. The thermodynamic characteristic of these processes under different conditions of temperatures and pressures has been explored in this paper. The results indicate that K-feldspar, albite and anorthite conversion to kaolinite and iUite respectively are all spontaneous reaction in diagenesis environment. The minimum of Gibbs free energy increment arid high positive temperature effects involved in anorthite dissolution reaction demonstrated that it is most instable and is more easily to be decomposed under low tempterature. K-feldspar dissolution reaction shows the maximum Gibbs flee energy increment and strong negative temperature dependence, which shows higher stabitity and high temperature solubility of K-feldspar. Albite dissolution reaction with moderate increment of Gibbs free energy is not affected obviously by temperature. Compared to temperature, the pressure has no obviously effect on the Gibbs free energy increment of reactions. Therefore, the secondary porosity, especially porosity formed in burial diagenesis environment, strongly depend on the K-feldspar, then on the albite. However, it seems that smectite-to-illite conversion should influence the albite dissolution and caused albitization or albite precipitation.
出处
《地质通报》
CAS
CSCD
北大核心
2009年第4期474-482,共9页
Geological Bulletin of China
基金
油气藏地质及开发工程国家重点实验室开放基金项目<储层砂岩重要成岩反应的实验模拟及其热力学研究>(编号:PLN9919)资助
关键词
长石
溶解反应
热力学
次生孔隙
feldspar
dissolution reaction
thermodynamics
secondary porosity
