Alkaline Dissolution of Sandstone in the Triassic Yanchang Formation in the Ordos Basin
TIAN Jian-feng1,2,3,LIU Chi-yang1,2,WANG Gui-cheng3,QIU Xin-wei1,2 1.State Key Laboratory of Continental Dynamics,Northwest University,Xi'an 710069,China 2.Institute of Oil and Gas of Northwest University,Xi'an 710069,China 3.College of Oil & Gas Resources,Xi'an Shiyou University,Xi'an 710065,China
In order to figure out the relationship between reservoir porosity and iron-rich chlorite cementation,the pore characteristic,rock constituents and relationship between pore and rock constituents of sandstone were studied by using cast thin sections,scanning electron microscope and electron microprobe techniques. The study reveals that the pore-line chlorite offers limited protection to the porosity,and the greatest contribution to the porosity is alkaline dissolution of volcanic materials. The volcanic materials (matrix and grain) belong to medium-basic volcanics through quantitative calculation of iron content in the chlorite cementation. During the early diagenetic stage,A 7%-11% medium-basic volcanics were dissolved,and this alkaine dissolution process yielded 8% secondary porosity and 3% pore-lining chlorite. The widespread chlorite cementation just indicates that abundant medium-basic volcanics were dissolved and considerable alkaline dissolution pore was generated.