| Dolomite reservoir of Sinian Dengying Formation in northern Sichuan Basin, an important field for following exploration, some issues about that need to be studied. Based on petrology observation and experimental analysis, it is shown that reservoirs mainly developed in rocks such as particle adhesion dolomite, laminated microorganism dolomite, and grained dolomite in Dengying Member-2 and Member-4, with major reservoir spaces of secondary dissolution pores and vugs. Among the four types of reservoirs including pore-vug, pore, pore-fracture, and vug, the reservoir quality of pore-fracture type is the best. As for the development of dolomite reservoir in Dengying Formation, the sediment of mound-shoal facies is the material basis, and the reconstruction of diagenesis is the key element. The total thickness of mound-shoal sediment of Member-2 is bigger than that of Member-4, but the porosity and permeability of Member-2 is smaller. Based on macroscopic evolution and microscopic pore features of the reservoir, two models are setup for Member-2 and Member-4 respectively. The epigenic karstification is predominant in Member-2 with the cementation of dolomites and the filling of slim sediments from overlying strata, while the burial dissolution is predominant in Member-4 with extensive dissolution accompanied by recrystallization and the filling of silicoide and asphalt in dissolution pores. According to the models, the good reservoirs in Dengying Member-2 develop at the overlap parts of hyporheic zone and mound-shoal, and the reservoirs in Member-4 go poor towards the inner part of the carbonate platform, and towards the lower part of the member. |
