Diagenesis and Reservoir Quality of the Sixth Member Sandstone of Yanchang Formation from Houxing Region, Ordos Basin, West of China

The sixth member sandstone of Yanchang formation in Houxing region is mainly fine grained arkose. Diagenetic minerals include grain-coating chlorite, laumontite, calcite and quartz cement, as well as overgrowth feldspar, illite, albite and so on. The development of grain-coating chlorite contributes to the conservation of original intergranular pores. Secondary pores, consisting of dissolved intergranular pores, dissolved skeletal pores, dissolved pores of laumontite and microcrack, significantly develop in the sixth sandstone. The relic intergranular pores and dissolved pores of laumontite are the most important pore types in the sixth member sandstone which has experienced complex diagenetic changes. The sixth member sandstone of Yanchang formation is experiencing stage A of telodiagenesis. Reservoir quality is obviously controlled by deposition and diagenesis.