鄂尔多斯盆地上古生界天然气储集层长石的溶蚀与次生孔隙的形成

Feldspar corrosion and secondary pore formation in the Upper Paleozoic gas reservoir, Ordos Basin

鄂尔多斯盆地上古生界天然气储集层主要为二叠系山西组山2段和下石盒子组盒8段,主要孔隙类型为次生孔隙。镜下观察,次生孔隙的形成除了与沉积物源、沉积环境和搬运介质有关外,还与后期成岩阶段长石的溶蚀作用有关。根据长石溶蚀的岩石学证据,建立反应方程式对长石溶蚀进行计算,综合考虑溶蚀的温度、反应的热力学趋势、体积的减小等因素,认为钾长石溶蚀可提供较大的次生孔隙,钙长石和钠长石溶蚀效果较差。在有机酸参与下碱性长石的溶蚀作用是该区天然气储集层次生孔隙形成的主要原因。

The Upper Paleozoic gas reservoir in the Ordos Basin mainly consists of Shan 2 gas layer in Shanxi Formation and He 8 gas layer in Xiashihezi Formation, Permian. The formation of secondary pore is mainly the result of feldspar corrosion according to a scanning electron microscope study. Calculation on feldspar corrosion from the perspective of thermodynamics, with reference to volume effect, proves that most secondary pore in the formation could be developed by the potash feldspar corrosion, and in this respect anorthite and albite corrosion is less effective. Analysis on possible sources of organic acid is conducted. All the studies indicate that the main cause of the formation of secondary pore in the gas reservoir is the corrosion of alkali feldspar with the effect of organic acid.