<sup>2</sup> Siliceous cementation

Siliceous cement is the product precipitated by siliceous materials in acid fluid and it is formed by the surrounding quartz particles or regions with poor development of chlorite film. In the study area, there's a universal development of siliceous types of cement in the Chang 8 reservoir, which is mainly manifested as the secondary expansion of quartz (Figure 4h). The thickness of the expanded sides ranges between 0.02~0.2 mm. The quartz particles still exist in residual inter-granular pores after the second expansion is generated.
