| Based on the analysis of field outcrops, well logging and core data, the sedimentary facies types and features of the Lower Cambrian Longwangmiao Formation in northern Sichuan Basin are discussed, and their influences on reservoirs are analyzed. During Early Cambrian Longwangmiao period, the sedimentary environment in northern Sichuan Basin was carbonate platform, which developed three types of facies including tidal flat, restricted platform and open platform, which were further subdivided into four types of subfacies: mixed tidal flat, intra-platform shoal, lagoon and interbank sea. The mixed tidal flat was mainly composed of sandy dolomite and dolomite, and tidal channels were visible in some areas. The intra-platform shoal was mainly composed of doloarenite with small deposition thickness. The lagoon mainly consisted of dolomite lagoon and dolomitic-limy lagoon with large distribution area. The deposition of interbank sea was mainly composed of dark gray massive limestone with intercalated dolomitic mottled limestone. The Longwangmiao period is composed of two regressive cycles in most areas, and lagoon mainly developed in the middle and lower part of a single sedimentary cycle, and intra-platform shoal mainly developed in the middle and upper part of a sedimentary cycle with thin single layer, and the mixed tidal flat mainly developed at the top of a sedimentary cycle. Due to the influence of paleocontinents, the sediment source supply decreased and the water depth gradually deepened, and the sedimentary facies translated from tidal flat to restricted platform to open platform successively from west to east in the study area. The intra-platform shoal mainly distributed around the restricted lagoon. Combined with the analysis of reservoir property of different sedimentary faces, it is concluded that grain dolomite depositing on the intra-platform shoal have the best reservoir property, followed by the crystalline dolomite, and the gypsum was the worst. Therefore, the most favorable sedimentary environment for reservoir development in Longwangmiao Formation is intra-platform shoal.
Key words： HUANG Zisang： Master in progress, major in sedimentary and reservoir geology. Add: No. 8 Xindu Avenue, School of Earth Science and Technology, Southwest Petroleum University, Chengdu, Sichuan 610500, China |
