Diagenesis and evolution of pores in clastic rock reservoir of Early Cretaceous in Chagan sag
Guo Dianbin, Li Cong, Li Zhong, Wang Yaming, Chen GangZhang, Han Lihui, Kong Hairui, Du Wenzhe
1. Research Institute of Exploration and Development, Zhongyuan Oilfield, SINOPEC, Puyang, Henan 457001;
2. College of Physics and Information Engineering of the Earth, China University of Petroleum, Beijing 102249;
3. Jidong Oilfield Company, PetroChina, Tangshan, Hebei 063004;
4. Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029;
5. Downhole Service Company of Chuanqing Misering Engineering Co. , Ltd., PetroChina, Xi'an 710018
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 K1s2 and K1w 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 of primary porosity, and at the same time the dissolution of feldspar and carbonate cements widens porosity. In the deep clastic reservoirs(>2 500 m)except the compaction, carbonate cementation is the main reason for lower porosity; the higher porosity is mainly composed of secondary solution pores caused by the mixture of the early acidic dissolution and late alkaline dissolution. The late alkaline dissolution occurred after the oil and gas entering, so the solution pores are invalid.