The Formation Mechanism And Distribution Regularity Of Reef-Bank Reserviors Of Lower Palaeozoic In North China

Reef and bank are important types of carbonate, also good reservoirs for oil and gas. According to the theory of carbonate sedimentary, petrology, carbonate reservoir geology, sequence stratigraphy, making full use of drilling and logging data, we divided the sequence stratigraphy of the lower Paleozoic in North China on the basis of field outcrop and core observation, established the chronological stratigraphic framework. We studied the sedimentary facies and sedimentary system within the chronological stratigraphic framework, then studied the distribution regularity and influence factors of reef-bank reservoirs.The lower Palaeozoic is diveded into two second-grade sequences,14 third-grade sequences in North China. Six sedimentary facies are identified which are tidal flat facies, restricted platform facies, open platform facies, shallow continental shelf, bank facies and reef facies. By doing correlation profile of sedimentary facies and lithofacies-paleogeographic maps, we know the spatial distribution regularity of sedimentary facies. Reef mainly develops in Zhangxia age, Gushan-Changshan age and the middle of Daruiweier age. Bank develops from middle Cambrian to early Ordovician, including Maozhuang age, Xuzhuang age, Zhangxia age of middle Cambrian; Gushan-Changshan age, Fengshan age of late Cambrian; Xinchang age, Daobaowan age of early Ordovician. Bank develops in shore bank and platform bank environment from Maozhuang age to Xuzhuang age when it is muddy water with the deposition of clastic rock and carbonate. After Zhangxia age, bank mainly develops in the environment of platform bank where the water is clear. From Maozhuang to Gushan-Changshan age, the platform bank is mainly oolitic bank. After Fengshan age, the platform is mainly limstone conglomerate bank. Zhangxia age is the most prosperous period of reef and bank with the widest distribution and max thickness in lower Palaeozoic in North China. The pore, cave and cracks are the main reservoir space of reef-bank reservoirs in lower Palaeozoic in North China. Tectonics, paleogeography and diagenesis are of important influence on the reef and bank reservoirs. Dolomitization, dissolition and moderate recrystallization are significant for the improvement of the reservoir physical property. On the basis of above study, I predict that North Zhengzhou, North of Anhui province, Jinan and Linyi of Shandong provience are good reservoir zone in Zhangxia age, and Huaibei in Anhui province is good reservoir zone in Gushan-Changshan age.