Diagenesis and evolution of pores in clastic rock reservoir of Early Cretaceous in Chagan sag

On the basis of the analysis of a number of rock slices and drill cores observation, combined with the means of scanning electron microscopy, whole-rock analysis, X-ray diffraction clay analysis and inclusion thermometry, study has been done about the diagensis of clastic rock reservoir and pore evolution in Chagan depression. The findings show that the reservoir is mainly composed of lithic arkoses with low contents maturity and low structure maturity. And its' diagenesis presents the "two strong-two weak" diagenetic characteristics: strong compaction, strong cementation, weak metasomasis, and weak dissolution; the diagenetic stage is in the diagenetic A period, and in some areas, the diagenetic stage is up to the the diagenetic B to late diagenetic. The cement of two stages mainly occurred in the early K(1)s(2) and K(1)w period. In the middle-shallow layer(< 2 500 m) the lower porosity is mainly caused by the strong compaction and early cementation. The higher porosity is caused by the better preservation o