DIAGENESIS AND ITS ROLE ON THE RESERVOIR OF ORDOVICIAN CARBONATE ROCKS IN THE WEST SHANDONG RISE
Zhang Yunfeng1 Li Zhong2 Wang Qingchen2 Kong Qingyou3 (1.Department of Exploration, Daqing Petroleum Institute, Daqing, Helongjiang 163318; 2.Institute of Geology and Geophysics, Chinese Academy Sciences, Beijing 100029; 3.Department of Earth Science, Nanjing University, Nanjing 210093)
Based on observation and survey in the West Shandong Rise, a piece of composite column was charted, and four depositional cycles and two unconformities were recognized. Applying synthetic techniques such as casting and slicing, the diagenetic successions, the pores' evolution characteristics were studied systematically. The results showed that the Ordovician carbonate rocks in the West Shandong Rise underwent multi-stages of sedimentation—burial—supergene—reburial—supergene and more types of diagenesis such as compaction, cementation, dolomitization, silicification, pressolution, dissolusion, etc. They could be classified into two sorts: constructive diagenesis and destructive one. The former included dolomitization, pressolution,solution and fracturing which produced a great deal of secondary pores and improved the reservoir; the latter included recrystallization, silicification, cementation and compaction and filling which reduced the porosity and permeability of the carbonate rocks. The carbonate rocks of Sanshanzi Formation underwent more once short supergene and burial stages subsequently than that of the Majiagou Formation. Secondary porosity and fracture system developed in the fine-coarse crystalline dolostones of the Sanshanzi Formation, the silt-fine crystalline dolostones of the Donghuangshan, Tuyu and Gezhuang Members of Majiagou Formation, and the carbonate breccias under the unconformable surface in the Badou Member of Majiagou Formation. All of them were potential reservoir sections.