Two types of reservoirs occur in the Feixianguan Formation in northeastern Sichuan Basin, namely oolitic dolomite of exposed shoal facies on platform margins and oolitic limestone of shoal facies on platform mar- gins. Based on an integrated analysis of various data including thin section observation, cathodoluminescence, scanning electron microscope and inclusion thermometry,a study of the characteristics of oolitic shoal reservoirs and their diagenesis is made in combination with the research on the tectonic strength and phases of the Yuanba area since the Indo-Chinese epoch. The results show that the physical properties of oolitic dolomite reservoirs in the Xuanhan-Daxian area are much better than those of oolitic limestone reservoirs in the Yuanba area. The oolitic dolomite reservoirs in the Xuanhan-Daxian area are characterized by greater intensity and multiple phases of diagenesis such as cataclasis,reerystallization and dissolution. The rocks experienced five phases of cataclasis and dissolution, among which the second, third and fifth phases were favorable for reservoir formation, and their recrystallization was strong. In contrast, the oolitic limestone reservoirs in the Yuanba area are featured by weaker strength and less phases of diagenesis such as cataclasis, recrystallization and dissolution. The rocks experienced three phases of cataclasis and dissolution,among which the second and third phases were favorable for reservoir development, and their recrysta]lization was weak. The macro-characteristics of dolomites show that the genesis of the oolitic dolomite is deposition rather than limestone metasomatism.
Oil ＆ Gas Geology
oolitic dolomite, oolitic limestone, cataclasis, recrystallization, dissolution, dolomitization, Feixianguan Formation,northeastern Sichuan Basin