咸化湖盆碎屑岩储层中铁白云石的溶蚀作用模拟实验研究

Simulation experiment for ankerite dissolution in clastic reservoir of saline lacustrine basin

  • 摘要: 一般研究认为岩石中的碳酸盐矿物在酸性条件下易发生溶蚀作用从而生成次生孔隙,进而增大岩石的储集空间和渗透性。柴达木盆地砂西地区始新统下干柴沟组碎屑岩储层为咸化湖盆沉积,偏光显微镜下和扫描电镜下可见石膏和铁白云石较为发育。通过流体—岩石动力学模拟实验研究得出,在地层条件下高温高压环境中铁白云石易发生溶蚀作用从而形成次生孔隙,石膏在其中起催化作用;铁白云石溶蚀生成的铁、镁离子为高岭石转化为绿泥石提供了必要的物质条件,生成的针叶状绿泥石极易堵塞较细的孔隙喉道造成了岩石渗透率的下降,但铁白云石等易溶矿物的溶蚀作用增加了岩石的孔隙度。

     

    Abstract: It is generally believed that carbonate minerals can easily dissolve. This process will lead to the formation of secondary pores, thereby enlarging the reservoir space and improving the permeability of reservoir rocks. In the Qaidam Basin, clastic reservoirs of the Lower Eocene Gancaigou Formation are deposits of saline lacustrine basin, with plaster and ankerite well developed in rock flacks as revealed by polarized light microscopy and scanning electron microscope. Experimental results of fluid-rock dynamic stimulation show that the ankerite dissolution can generate secondary pores, and gypsum catalyzes the dissolution. The iron and magnesium ions generated are reactants in the transformation from koalinite to chlorite. The foliated chlorite easily blocks thin throat, leading to the decrease of permeability, while the dissolution of easily soluble minerals like ankerite increases porosity.

     

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